diff --git a/adb/transport.cpp b/adb/transport.cpp
index 76a31ce..8741654 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -764,6 +764,10 @@
 #if ADB_HOST
         if (t->IsTcpDevice() && !t->kicked()) {
             D("transport: %s unref (attempting reconnection)", t->serial.c_str());
+
+            // We need to clear the transport's keys, so that on the next connection, it tries
+            // again from the beginning.
+            t->ResetKeys();
             reconnect_handler.TrackTransport(t);
         } else {
             D("transport: %s unref (kicking and closing)", t->serial.c_str());
@@ -1328,10 +1332,20 @@
 
 #if ADB_HOST
 std::shared_ptr<RSA> atransport::NextKey() {
-    if (keys_.empty()) keys_ = adb_auth_get_private_keys();
+    if (keys_.empty()) {
+        LOG(INFO) << "fetching keys for transport " << this->serial_name();
+        keys_ = adb_auth_get_private_keys();
+
+        // We should have gotten at least one key: the one that's automatically generated.
+        CHECK(!keys_.empty());
+    }
 
     std::shared_ptr<RSA> result = keys_[0];
     keys_.pop_front();
     return result;
 }
+
+void atransport::ResetKeys() {
+    keys_.clear();
+}
 #endif
diff --git a/adb/transport.h b/adb/transport.h
index 9894bdf..d593700 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -258,6 +258,7 @@
 
 #if ADB_HOST
     std::shared_ptr<RSA> NextKey();
+    void ResetKeys();
 #endif
 
     char token[TOKEN_SIZE] = {};
diff --git a/base/logging.cpp b/base/logging.cpp
index bd09069..f89168c 100644
--- a/base/logging.cpp
+++ b/base/logging.cpp
@@ -417,6 +417,14 @@
   }
   std::string msg(data_->ToString());
 
+  if (data_->GetSeverity() == FATAL) {
+#ifdef __ANDROID__
+    // Set the bionic abort message early to avoid liblog doing it
+    // with the individual lines, so that we get the whole message.
+    android_set_abort_message(msg.c_str());
+#endif
+  }
+
   {
     // Do the actual logging with the lock held.
     std::lock_guard<std::mutex> lock(LoggingLock());
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index fee0857..b717aef 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -1541,7 +1541,7 @@
         return false;
     }
     auto path = find_item_given_name("super_empty.img");
-    if (path.empty()) {
+    if (path.empty() || access(path.c_str(), R_OK)) {
         return false;
     }
     auto metadata = android::fs_mgr::ReadFromImageFile(path);
diff --git a/fs_mgr/fs_mgr.cpp b/fs_mgr/fs_mgr.cpp
index 750ed71..60ce452 100644
--- a/fs_mgr/fs_mgr.cpp
+++ b/fs_mgr/fs_mgr.cpp
@@ -83,6 +83,8 @@
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof(*(a)))
 
 using android::base::Realpath;
+using android::base::StartsWith;
+using android::base::unique_fd;
 using android::dm::DeviceMapper;
 using android::dm::DmDeviceState;
 using android::fs_mgr::AvbHandle;
@@ -525,26 +527,15 @@
     }
 }
 
-/*
- * Mark the given block device as read-only, using the BLKROSET ioctl.
- * Return 0 on success, and -1 on error.
- */
-int fs_mgr_set_blk_ro(const char *blockdev)
-{
-    int fd;
-    int rc = -1;
-    int ON = 1;
-
-    fd = TEMP_FAILURE_RETRY(open(blockdev, O_RDONLY | O_CLOEXEC));
+// Mark the given block device as read-only, using the BLKROSET ioctl.
+bool fs_mgr_set_blk_ro(const std::string& blockdev) {
+    unique_fd fd(TEMP_FAILURE_RETRY(open(blockdev.c_str(), O_RDONLY | O_CLOEXEC)));
     if (fd < 0) {
-        // should never happen
-        return rc;
+        return false;
     }
 
-    rc = ioctl(fd, BLKROSET, &ON);
-    close(fd);
-
-    return rc;
+    int ON = 1;
+    return ioctl(fd, BLKROSET, &ON) == 0;
 }
 
 // Orange state means the device is unlocked, see the following link for details.
@@ -712,82 +703,65 @@
     return 0;
 }
 
-static int translate_ext_labels(struct fstab_rec *rec)
-{
-    DIR *blockdir = NULL;
-    struct dirent *ent;
-    char *label;
-    size_t label_len;
-    int ret = -1;
-
-    if (strncmp(rec->blk_device, "LABEL=", 6))
-        return 0;
-
-    label = rec->blk_device + 6;
-    label_len = strlen(label);
-
-    if (label_len > 16) {
-        LERROR << "FS label is longer than allowed by filesystem";
-        goto out;
+static bool TranslateExtLabels(fstab_rec* rec) {
+    if (!StartsWith(rec->blk_device, "LABEL=")) {
+        return true;
     }
 
+    std::string label = rec->blk_device + 6;
+    if (label.size() > 16) {
+        LERROR << "FS label is longer than allowed by filesystem";
+        return false;
+    }
 
-    blockdir = opendir("/dev/block");
+    auto blockdir = std::unique_ptr<DIR, decltype(&closedir)>{opendir("/dev/block"), closedir};
     if (!blockdir) {
         LERROR << "couldn't open /dev/block";
-        goto out;
+        return false;
     }
 
-    while ((ent = readdir(blockdir))) {
-        int fd;
-        char super_buf[1024];
-        struct ext4_super_block *sb;
-
+    struct dirent* ent;
+    while ((ent = readdir(blockdir.get()))) {
         if (ent->d_type != DT_BLK)
             continue;
 
-        fd = openat(dirfd(blockdir), ent->d_name, O_RDONLY);
+        unique_fd fd(TEMP_FAILURE_RETRY(
+                openat(dirfd(blockdir.get()), ent->d_name, O_RDONLY | O_CLOEXEC)));
         if (fd < 0) {
             LERROR << "Cannot open block device /dev/block/" << ent->d_name;
-            goto out;
+            return false;
         }
 
+        ext4_super_block super_block;
         if (TEMP_FAILURE_RETRY(lseek(fd, 1024, SEEK_SET)) < 0 ||
-            TEMP_FAILURE_RETRY(read(fd, super_buf, 1024)) != 1024) {
-            /* Probably a loopback device or something else without a readable
-             * superblock.
-             */
-            close(fd);
+            TEMP_FAILURE_RETRY(read(fd, &super_block, sizeof(super_block))) !=
+                    sizeof(super_block)) {
+            // Probably a loopback device or something else without a readable superblock.
             continue;
         }
 
-        sb = (struct ext4_super_block *)super_buf;
-        if (sb->s_magic != EXT4_SUPER_MAGIC) {
+        if (super_block.s_magic != EXT4_SUPER_MAGIC) {
             LINFO << "/dev/block/" << ent->d_name << " not ext{234}";
             continue;
         }
 
-        if (!strncmp(label, sb->s_volume_name, label_len)) {
-            char *new_blk_device;
+        if (label == super_block.s_volume_name) {
+            char* new_blk_device;
 
             if (asprintf(&new_blk_device, "/dev/block/%s", ent->d_name) < 0) {
                 LERROR << "Could not allocate block device string";
-                goto out;
+                return false;
             }
 
-            LINFO << "resolved label " << rec->blk_device << " to "
-                  << new_blk_device;
+            LINFO << "resolved label " << rec->blk_device << " to " << new_blk_device;
 
             free(rec->blk_device);
             rec->blk_device = new_blk_device;
-            ret = 0;
-            break;
+            return true;
         }
     }
 
-out:
-    closedir(blockdir);
-    return ret;
+    return false;
 }
 
 static bool needs_block_encryption(const struct fstab_rec* rec)
@@ -966,9 +940,8 @@
                 LERROR << rec->fs_type << " does not implement checkpoints.";
             }
         } else if (fs_mgr_is_checkpoint_blk(rec)) {
-            android::base::unique_fd fd(
-                    TEMP_FAILURE_RETRY(open(rec->blk_device, O_RDONLY | O_CLOEXEC)));
-            if (!fd) {
+            unique_fd fd(TEMP_FAILURE_RETRY(open(rec->blk_device, O_RDONLY | O_CLOEXEC)));
+            if (fd < 0) {
                 PERROR << "Cannot open device " << rec->blk_device;
                 return false;
             }
@@ -1032,8 +1005,9 @@
     for (i = 0; i < fstab->num_entries; i++) {
         /* Don't mount entries that are managed by vold or not for the mount mode*/
         if ((fstab->recs[i].fs_mgr_flags & (MF_VOLDMANAGED | MF_RECOVERYONLY)) ||
-             ((mount_mode == MOUNT_MODE_LATE) && !fs_mgr_is_latemount(&fstab->recs[i])) ||
-             ((mount_mode == MOUNT_MODE_EARLY) && fs_mgr_is_latemount(&fstab->recs[i]))) {
+            ((mount_mode == MOUNT_MODE_LATE) && !fs_mgr_is_latemount(&fstab->recs[i])) ||
+            ((mount_mode == MOUNT_MODE_EARLY) && fs_mgr_is_latemount(&fstab->recs[i])) ||
+            fs_mgr_is_first_stage_mount(&fstab->recs[i])) {
             continue;
         }
 
@@ -1055,8 +1029,7 @@
 
         /* Translate LABEL= file system labels into block devices */
         if (is_extfs(fstab->recs[i].fs_type)) {
-            int tret = translate_ext_labels(&fstab->recs[i]);
-            if (tret < 0) {
+            if (!TranslateExtLabels(&fstab->recs[i])) {
                 LERROR << "Could not translate label to block device";
                 continue;
             }
@@ -1157,12 +1130,12 @@
 
             if (fs_mgr_is_encryptable(&fstab->recs[top_idx]) &&
                 strcmp(fstab->recs[top_idx].key_loc, KEY_IN_FOOTER)) {
-                int fd = open(fstab->recs[top_idx].key_loc, O_WRONLY);
+                unique_fd fd(TEMP_FAILURE_RETRY(
+                        open(fstab->recs[top_idx].key_loc, O_WRONLY | O_CLOEXEC)));
                 if (fd >= 0) {
                     LINFO << __FUNCTION__ << "(): also wipe "
                           << fstab->recs[top_idx].key_loc;
                     wipe_block_device(fd, get_file_size(fd));
-                    close(fd);
                 } else {
                     PERROR << __FUNCTION__ << "(): "
                            << fstab->recs[top_idx].key_loc << " wouldn't open";
diff --git a/fs_mgr/fs_mgr_dm_linear.cpp b/fs_mgr/fs_mgr_dm_linear.cpp
index fe0e039..3f075ef 100644
--- a/fs_mgr/fs_mgr_dm_linear.cpp
+++ b/fs_mgr/fs_mgr_dm_linear.cpp
@@ -51,12 +51,20 @@
 using DmTargetZero = android::dm::DmTargetZero;
 using DmTargetLinear = android::dm::DmTargetLinear;
 
-bool GetPhysicalPartitionDevicePath(const LpMetadataBlockDevice& block_device,
-                                    std::string* result) {
+static bool GetPhysicalPartitionDevicePath(const LpMetadata& metadata,
+                                           const LpMetadataBlockDevice& block_device,
+                                           const std::string& super_device,
+                                           std::string* result) {
     // Note: device-mapper will not accept symlinks, so we must use realpath
     // here.
     std::string name = GetBlockDevicePartitionName(block_device);
     std::string path = "/dev/block/by-name/" + name;
+    // If the super device is the source of this block device's metadata,
+    // make sure we use the correct super device (and not just "super",
+    // which might not exist.)
+    if (GetMetadataSuperBlockDevice(metadata) == &block_device) {
+        path = super_device;
+    }
     if (!android::base::Realpath(path, result)) {
         PERROR << "realpath: " << path;
         return false;
@@ -65,7 +73,7 @@
 }
 
 static bool CreateDmTable(const LpMetadata& metadata, const LpMetadataPartition& partition,
-                          DmTable* table) {
+                          const std::string& super_device, DmTable* table) {
     uint64_t sector = 0;
     for (size_t i = 0; i < partition.num_extents; i++) {
         const auto& extent = metadata.extents[partition.first_extent_index + i];
@@ -77,7 +85,7 @@
             case LP_TARGET_TYPE_LINEAR: {
                 const auto& block_device = metadata.block_devices[extent.target_source];
                 std::string path;
-                if (!GetPhysicalPartitionDevicePath(block_device, &path)) {
+                if (!GetPhysicalPartitionDevicePath(metadata, block_device, super_device, &path)) {
                     LOG(ERROR) << "Unable to complete device-mapper table, unknown block device";
                     return false;
                 }
@@ -102,11 +110,11 @@
 
 static bool CreateLogicalPartition(const LpMetadata& metadata, const LpMetadataPartition& partition,
                                    bool force_writable, const std::chrono::milliseconds& timeout_ms,
-                                   std::string* path) {
+                                   const std::string& super_device, std::string* path) {
     DeviceMapper& dm = DeviceMapper::Instance();
 
     DmTable table;
-    if (!CreateDmTable(metadata, partition, &table)) {
+    if (!CreateDmTable(metadata, partition, super_device, &table)) {
         return false;
     }
     if (force_writable) {
@@ -137,7 +145,7 @@
         LOG(ERROR) << "Could not read partition table.";
         return true;
     }
-    return CreateLogicalPartitions(*metadata.get());
+    return CreateLogicalPartitions(*metadata.get(), block_device);
 }
 
 std::unique_ptr<LpMetadata> ReadCurrentMetadata(const std::string& block_device) {
@@ -145,14 +153,14 @@
     return ReadMetadata(block_device.c_str(), slot);
 }
 
-bool CreateLogicalPartitions(const LpMetadata& metadata) {
+bool CreateLogicalPartitions(const LpMetadata& metadata, const std::string& super_device) {
     for (const auto& partition : metadata.partitions) {
         if (!partition.num_extents) {
             LINFO << "Skipping zero-length logical partition: " << GetPartitionName(partition);
             continue;
         }
         std::string path;
-        if (!CreateLogicalPartition(metadata, partition, false, {}, &path)) {
+        if (!CreateLogicalPartition(metadata, partition, false, {}, super_device, &path)) {
             LERROR << "Could not create logical partition: " << GetPartitionName(partition);
             return false;
         }
@@ -171,7 +179,7 @@
     for (const auto& partition : metadata->partitions) {
         if (GetPartitionName(partition) == partition_name) {
             return CreateLogicalPartition(*metadata.get(), partition, force_writable, timeout_ms,
-                                          path);
+                                          block_device, path);
         }
     }
     LERROR << "Could not find any partition with name: " << partition_name;
diff --git a/fs_mgr/fs_mgr_fstab.cpp b/fs_mgr/fs_mgr_fstab.cpp
index 31b0944..0fde22e 100644
--- a/fs_mgr/fs_mgr_fstab.cpp
+++ b/fs_mgr/fs_mgr_fstab.cpp
@@ -57,7 +57,7 @@
 
 struct flag_list {
     const char *name;
-    int flag;
+    unsigned int flag;
 };
 
 static struct flag_list mount_flags[] = {
@@ -102,6 +102,7 @@
         {"formattable", MF_FORMATTABLE},
         {"slotselect", MF_SLOTSELECT},
         {"nofail", MF_NOFAIL},
+        {"first_stage_mount", MF_FIRST_STAGE_MOUNT},
         {"latemount", MF_LATEMOUNT},
         {"reservedsize=", MF_RESERVEDSIZE},
         {"quota", MF_QUOTA},
@@ -998,6 +999,10 @@
     return fstab->fs_mgr_flags & MF_NOFAIL;
 }
 
+int fs_mgr_is_first_stage_mount(const struct fstab_rec* fstab) {
+    return fstab->fs_mgr_flags & MF_FIRST_STAGE_MOUNT;
+}
+
 int fs_mgr_is_latemount(const struct fstab_rec* fstab) {
     return fstab->fs_mgr_flags & MF_LATEMOUNT;
 }
diff --git a/fs_mgr/fs_mgr_overlayfs.cpp b/fs_mgr/fs_mgr_overlayfs.cpp
index fdfe1c0..649c8bf 100644
--- a/fs_mgr/fs_mgr_overlayfs.cpp
+++ b/fs_mgr/fs_mgr_overlayfs.cpp
@@ -74,7 +74,7 @@
     return false;
 }
 
-bool fs_mgr_overlayfs_mount_all(const std::vector<const fstab_rec*>&) {
+bool fs_mgr_overlayfs_mount_all(const std::vector<fstab_rec*>&) {
     return false;
 }
 
@@ -82,7 +82,7 @@
     return {};
 }
 
-std::vector<std::string> fs_mgr_overlayfs_required_devices(const std::vector<const fstab_rec*>&) {
+std::vector<std::string> fs_mgr_overlayfs_required_devices(const std::vector<fstab_rec*>&) {
     return {};
 }
 
@@ -840,7 +840,7 @@
     return ret;
 }
 
-bool fs_mgr_overlayfs_mount_all(const std::vector<const fstab_rec*>& fsrecs) {
+bool fs_mgr_overlayfs_mount_all(const std::vector<fstab_rec*>& fsrecs) {
     std::vector<fstab_rec> recs;
     for (const auto& rec : fsrecs) recs.push_back(*rec);
     fstab fstab = {static_cast<int>(fsrecs.size()), &recs[0]};
@@ -863,8 +863,7 @@
     return {};
 }
 
-std::vector<std::string> fs_mgr_overlayfs_required_devices(
-        const std::vector<const fstab_rec*>& fsrecs) {
+std::vector<std::string> fs_mgr_overlayfs_required_devices(const std::vector<fstab_rec*>& fsrecs) {
     std::vector<fstab_rec> recs;
     for (const auto& rec : fsrecs) recs.push_back(*rec);
     fstab fstab = {static_cast<int>(fsrecs.size()), &recs[0]};
diff --git a/fs_mgr/fs_mgr_priv.h b/fs_mgr/fs_mgr_priv.h
index 711446c..faef34b 100644
--- a/fs_mgr/fs_mgr_priv.h
+++ b/fs_mgr/fs_mgr_priv.h
@@ -118,6 +118,8 @@
 #define MF_LOGICAL        0x10000000
 #define MF_CHECKPOINT_BLK 0x20000000
 #define MF_CHECKPOINT_FS  0x40000000
+#define MF_FIRST_STAGE_MOUNT \
+                          0x80000000
 // clang-format on
 
 #define DM_BUF_SIZE 4096
@@ -130,7 +132,7 @@
                           const std::chrono::milliseconds relative_timeout,
                           FileWaitMode wait_mode = FileWaitMode::Exists);
 
-int fs_mgr_set_blk_ro(const char* blockdev);
+bool fs_mgr_set_blk_ro(const std::string& blockdev);
 bool fs_mgr_update_for_slotselect(Fstab* fstab);
 bool fs_mgr_is_device_unlocked();
 const std::string& get_android_dt_dir();
diff --git a/fs_mgr/include/fs_mgr_dm_linear.h b/fs_mgr/include/fs_mgr_dm_linear.h
index 66abfca..f065071 100644
--- a/fs_mgr/include/fs_mgr_dm_linear.h
+++ b/fs_mgr/include/fs_mgr_dm_linear.h
@@ -43,7 +43,7 @@
 
 // Create block devices for all logical partitions in the given metadata. The
 // metadata must have been read from the current slot.
-bool CreateLogicalPartitions(const LpMetadata& metadata);
+bool CreateLogicalPartitions(const LpMetadata& metadata, const std::string& block_device);
 
 // Create block devices for all logical partitions. This is a convenience
 // method for ReadMetadata and CreateLogicalPartitions.
diff --git a/fs_mgr/include/fs_mgr_overlayfs.h b/fs_mgr/include/fs_mgr_overlayfs.h
index 4537e38..0dd9121 100644
--- a/fs_mgr/include/fs_mgr_overlayfs.h
+++ b/fs_mgr/include/fs_mgr_overlayfs.h
@@ -22,10 +22,9 @@
 #include <vector>
 
 bool fs_mgr_overlayfs_mount_all(fstab* fstab);
-bool fs_mgr_overlayfs_mount_all(const std::vector<const fstab_rec*>& fstab);
+bool fs_mgr_overlayfs_mount_all(const std::vector<fstab_rec*>& fstab);
 std::vector<std::string> fs_mgr_overlayfs_required_devices(fstab* fstab);
-std::vector<std::string> fs_mgr_overlayfs_required_devices(
-        const std::vector<const fstab_rec*>& fstab);
+std::vector<std::string> fs_mgr_overlayfs_required_devices(const std::vector<fstab_rec*>& fstab);
 bool fs_mgr_overlayfs_setup(const char* backing = nullptr, const char* mount_point = nullptr,
                             bool* change = nullptr);
 bool fs_mgr_overlayfs_teardown(const char* mount_point = nullptr, bool* change = nullptr);
diff --git a/fs_mgr/include_fstab/fstab/fstab.h b/fs_mgr/include_fstab/fstab/fstab.h
index 80bdb87..4706028 100644
--- a/fs_mgr/include_fstab/fstab/fstab.h
+++ b/fs_mgr/include_fstab/fstab/fstab.h
@@ -84,6 +84,7 @@
 int fs_mgr_is_formattable(const struct fstab_rec* fstab);
 int fs_mgr_is_slotselect(const struct fstab_rec* fstab);
 int fs_mgr_is_nofail(const struct fstab_rec* fstab);
+int fs_mgr_is_first_stage_mount(const struct fstab_rec* fstab);
 int fs_mgr_is_latemount(const struct fstab_rec* fstab);
 int fs_mgr_is_quota(const struct fstab_rec* fstab);
 int fs_mgr_is_logical(const struct fstab_rec* fstab);
diff --git a/fs_mgr/liblp/builder.cpp b/fs_mgr/liblp/builder.cpp
index da86d75..699b9e7 100644
--- a/fs_mgr/liblp/builder.cpp
+++ b/fs_mgr/liblp/builder.cpp
@@ -578,6 +578,12 @@
     CHECK_NE(sectors_per_block, 0);
     CHECK(sectors_needed % sectors_per_block == 0);
 
+    if (IsABDevice() && !IsRetrofitDevice() && GetPartitionSlotSuffix(partition->name()) == "_b") {
+        // Allocate "a" partitions top-down and "b" partitions bottom-up, to
+        // minimize fragmentation during OTA.
+        free_regions = PrioritizeSecondHalfOfSuper(free_regions);
+    }
+
     // Find gaps that we can use for new extents. Note we store new extents in a
     // temporary vector, and only commit them if we are guaranteed enough free
     // space.
@@ -621,6 +627,40 @@
     return true;
 }
 
+std::vector<MetadataBuilder::Interval> MetadataBuilder::PrioritizeSecondHalfOfSuper(
+        const std::vector<Interval>& free_list) {
+    const auto& super = block_devices_[0];
+    uint64_t first_sector = super.first_logical_sector;
+    uint64_t last_sector = super.size / LP_SECTOR_SIZE;
+    uint64_t midpoint = first_sector + (last_sector - first_sector) / 2;
+
+    // Choose an aligned sector for the midpoint. This could lead to one half
+    // being slightly larger than the other, but this will not restrict the
+    // size of partitions (it might lead to one extra extent if "B" overflows).
+    midpoint = AlignSector(super, midpoint);
+
+    std::vector<Interval> first_half;
+    std::vector<Interval> second_half;
+    for (const auto& region : free_list) {
+        // Note: deprioritze if not the main super partition. Even though we
+        // don't call this for retrofit devices, we will allow adding additional
+        // block devices on non-retrofit devices.
+        if (region.device_index != 0 || region.end <= midpoint) {
+            first_half.emplace_back(region);
+            continue;
+        }
+        if (region.start < midpoint && region.end > midpoint) {
+            // Split this into two regions.
+            first_half.emplace_back(region.device_index, region.start, midpoint);
+            second_half.emplace_back(region.device_index, midpoint, region.end);
+        } else {
+            second_half.emplace_back(region);
+        }
+    }
+    second_half.insert(second_half.end(), first_half.begin(), first_half.end());
+    return second_half;
+}
+
 void MetadataBuilder::ShrinkPartition(Partition* partition, uint64_t aligned_size) {
     partition->ShrinkTo(aligned_size);
 }
@@ -930,5 +970,9 @@
     return android::base::GetBoolProperty("ro.build.ab_update", false);
 }
 
+bool MetadataBuilder::IsRetrofitDevice() const {
+    return GetBlockDevicePartitionName(block_devices_[0]) != LP_METADATA_DEFAULT_PARTITION_NAME;
+}
+
 }  // namespace fs_mgr
 }  // namespace android
diff --git a/fs_mgr/liblp/builder_test.cpp b/fs_mgr/liblp/builder_test.cpp
index 926fe12..7833a25 100644
--- a/fs_mgr/liblp/builder_test.cpp
+++ b/fs_mgr/liblp/builder_test.cpp
@@ -720,3 +720,41 @@
     ASSERT_EQ(builder->AddPartition("system", 0), nullptr);
     ASSERT_NE(builder->AddPartition("system_a", 0), nullptr);
 }
+
+TEST_F(BuilderTest, ABExtents) {
+    BlockDeviceInfo device_info("super", 10_GiB, 768 * 1024, 0, 4096);
+
+    // A and B slots should be allocated from separate halves of the partition,
+    // to mitigate allocating too many extents. (b/120433288)
+    MetadataBuilder::OverrideABForTesting(true);
+    auto builder = MetadataBuilder::New(device_info, 65536, 2);
+    ASSERT_NE(builder, nullptr);
+    Partition* system_a = builder->AddPartition("system_a", 0);
+    ASSERT_NE(system_a, nullptr);
+    Partition* system_b = builder->AddPartition("system_b", 0);
+    ASSERT_NE(system_b, nullptr);
+    ASSERT_TRUE(builder->ResizePartition(system_a, 2_GiB));
+    ASSERT_TRUE(builder->ResizePartition(system_b, 2_GiB));
+
+    builder->RemovePartition("system_a");
+    system_a = builder->AddPartition("system_a", 0);
+    ASSERT_NE(system_a, nullptr);
+    ASSERT_TRUE(builder->ResizePartition(system_a, 3_GiB));
+
+    EXPECT_EQ(system_a->extents().size(), static_cast<size_t>(1));
+    EXPECT_EQ(system_b->extents().size(), static_cast<size_t>(1));
+    ASSERT_TRUE(builder->ResizePartition(system_b, 6_GiB));
+    EXPECT_EQ(system_b->extents().size(), static_cast<size_t>(3));
+
+    unique_ptr<LpMetadata> exported = builder->Export();
+    ASSERT_NE(exported, nullptr);
+    ASSERT_EQ(exported->extents.size(), static_cast<size_t>(4));
+    EXPECT_EQ(exported->extents[0].target_data, 10487808);
+    EXPECT_EQ(exported->extents[0].num_sectors, 4194304);
+    EXPECT_EQ(exported->extents[1].target_data, 14682624);
+    EXPECT_EQ(exported->extents[1].num_sectors, 6288896);
+    EXPECT_EQ(exported->extents[2].target_data, 6292992);
+    EXPECT_EQ(exported->extents[2].num_sectors, 2099712);
+    EXPECT_EQ(exported->extents[3].target_data, 1536);
+    EXPECT_EQ(exported->extents[3].num_sectors, 6291456);
+}
diff --git a/fs_mgr/liblp/include/liblp/builder.h b/fs_mgr/liblp/include/liblp/builder.h
index 4bb38d6..f477b4b 100644
--- a/fs_mgr/liblp/include/liblp/builder.h
+++ b/fs_mgr/liblp/include/liblp/builder.h
@@ -275,6 +275,7 @@
                        const LpMetadataPartition& source);
     bool ImportPartition(const LpMetadata& metadata, const LpMetadataPartition& source);
     bool IsABDevice() const;
+    bool IsRetrofitDevice() const;
 
     struct Interval {
         uint32_t device_index;
@@ -294,6 +295,7 @@
     std::vector<Interval> GetFreeRegions() const;
     void ExtentsToFreeList(const std::vector<Interval>& extents,
                            std::vector<Interval>* free_regions) const;
+    std::vector<Interval> PrioritizeSecondHalfOfSuper(const std::vector<Interval>& free_list);
 
     static bool sABOverrideValue;
     static bool sABOverrideSet;
diff --git a/init/Android.bp b/init/Android.bp
index ea66ac6..e7b8516 100644
--- a/init/Android.bp
+++ b/init/Android.bp
@@ -19,6 +19,7 @@
     cpp_std: "experimental",
     sanitize: {
         misc_undefined: ["signed-integer-overflow"],
+        address: false,  // TODO(b/120561310): Fix ASAN to work without /proc mounted and re-enable.
     },
     cflags: [
         "-DLOG_UEVENTS=0",
diff --git a/init/Android.mk b/init/Android.mk
index 0e6ee0b..bdd0301 100644
--- a/init/Android.mk
+++ b/init/Android.mk
@@ -104,7 +104,6 @@
 LOCAL_REQUIRED_MODULES := \
    init_second_stage \
 
-LOCAL_POST_INSTALL_CMD := ln -sf /system/bin/init $(TARGET_ROOT_OUT)/init
 include $(BUILD_PHONY_PACKAGE)
 
 include $(CLEAR_VARS)
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index d35329e..c124656 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -84,7 +84,7 @@
 
     bool need_dm_verity_;
 
-    std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> device_tree_fstab_;
+    std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab_;
     std::string lp_metadata_partition_;
     std::vector<fstab_rec*> mount_fstab_recs_;
     std::set<std::string> required_devices_partition_names_;
@@ -132,15 +132,27 @@
 // Class Definitions
 // -----------------
 FirstStageMount::FirstStageMount()
-    : need_dm_verity_(false), device_tree_fstab_(fs_mgr_read_fstab_dt(), fs_mgr_free_fstab) {
-    if (device_tree_fstab_) {
-        // Stores device_tree_fstab_->recs[] into mount_fstab_recs_ (vector<fstab_rec*>)
-        // for easier manipulation later, e.g., range-base for loop.
-        for (int i = 0; i < device_tree_fstab_->num_entries; i++) {
-            mount_fstab_recs_.push_back(&device_tree_fstab_->recs[i]);
+    : need_dm_verity_(false), fstab_(fs_mgr_read_fstab_dt(), fs_mgr_free_fstab) {
+    // Stores fstab_->recs[] into mount_fstab_recs_ (vector<fstab_rec*>)
+    // for easier manipulation later, e.g., range-base for loop.
+    if (fstab_) {
+        // DT Fstab predated having a first_stage_mount fs_mgr flag, so if it exists, we use it.
+        for (int i = 0; i < fstab_->num_entries; i++) {
+            mount_fstab_recs_.push_back(&fstab_->recs[i]);
         }
     } else {
-        LOG(INFO) << "Failed to read fstab from device tree";
+        // Fstab found in first stage ramdisk, which should be a copy of the normal fstab.
+        // Mounts intended for first stage are explicitly flagged as such.
+        fstab_.reset(fs_mgr_read_fstab_default());
+        if (fstab_) {
+            for (int i = 0; i < fstab_->num_entries; i++) {
+                if (fs_mgr_is_first_stage_mount(&fstab_->recs[i])) {
+                    mount_fstab_recs_.push_back(&fstab_->recs[i]);
+                }
+            }
+        } else {
+            LOG(INFO) << "Failed to read fstab from device tree";
+        }
     }
 
     auto boot_devices = fs_mgr_get_boot_devices();
@@ -252,9 +264,10 @@
 }
 
 bool FirstStageMount::InitDmLinearBackingDevices(const android::fs_mgr::LpMetadata& metadata) {
-    auto partition_names = GetBlockDevicePartitionNames(metadata);
+    auto partition_names = android::fs_mgr::GetBlockDevicePartitionNames(metadata);
     for (const auto& partition_name : partition_names) {
-        if (partition_name == lp_metadata_partition_) {
+        const auto super_device = android::fs_mgr::GetMetadataSuperBlockDevice(metadata);
+        if (partition_name == android::fs_mgr::GetBlockDevicePartitionName(*super_device)) {
             continue;
         }
         required_devices_partition_names_.emplace(partition_name);
@@ -292,7 +305,7 @@
     if (!InitDmLinearBackingDevices(*metadata.get())) {
         return false;
     }
-    return android::fs_mgr::CreateLogicalPartitions(*metadata.get());
+    return android::fs_mgr::CreateLogicalPartitions(*metadata.get(), lp_metadata_partition_);
 }
 
 ListenerAction FirstStageMount::HandleBlockDevice(const std::string& name, const Uevent& uevent) {
@@ -411,7 +424,7 @@
     }
 
     // heads up for instantiating required device(s) for overlayfs logic
-    const auto devices = fs_mgr_overlayfs_required_devices(device_tree_fstab_.get());
+    const auto devices = fs_mgr_overlayfs_required_devices(mount_fstab_recs_);
     for (auto const& device : devices) {
         if (android::base::StartsWith(device, "/dev/block/by-name/")) {
             required_devices_partition_names_.emplace(basename(device.c_str()));
@@ -423,7 +436,7 @@
         }
     }
 
-    fs_mgr_overlayfs_mount_all(device_tree_fstab_.get());
+    fs_mgr_overlayfs_mount_all(mount_fstab_recs_);
 
     return true;
 }
diff --git a/libsysutils/Android.bp b/libsysutils/Android.bp
index 29d23c8..da5d86c 100644
--- a/libsysutils/Android.bp
+++ b/libsysutils/Android.bp
@@ -1,4 +1,4 @@
-cc_library_shared {
+cc_library {
     name: "libsysutils",
     vendor_available: true,
     vndk: {
diff --git a/libunwindstack/Elf.cpp b/libunwindstack/Elf.cpp
index 4d72ead..5b586a2 100644
--- a/libunwindstack/Elf.cpp
+++ b/libunwindstack/Elf.cpp
@@ -140,6 +140,10 @@
   return true;
 }
 
+bool Elf::GetBuildID(std::string* build_id) {
+  return valid_ && interface_->GetBuildID(build_id);
+}
+
 void Elf::GetLastError(ErrorData* data) {
   if (valid_) {
     *data = interface_->last_error();
diff --git a/libunwindstack/ElfInterface.cpp b/libunwindstack/ElfInterface.cpp
index f59a472..d0af94a 100644
--- a/libunwindstack/ElfInterface.cpp
+++ b/libunwindstack/ElfInterface.cpp
@@ -237,6 +237,56 @@
   }
 }
 
+template <typename NhdrType>
+bool ElfInterface::ReadBuildID(std::string* build_id) {
+  // Ensure there is no overflow in any of the calulations below.
+  uint64_t tmp;
+  if (__builtin_add_overflow(gnu_build_id_offset_, gnu_build_id_size_, &tmp)) {
+    return false;
+  }
+
+  uint64_t offset = 0;
+  while (offset < gnu_build_id_size_) {
+    if (gnu_build_id_size_ - offset < sizeof(NhdrType)) {
+      return false;
+    }
+    NhdrType hdr;
+    if (!memory_->ReadFully(gnu_build_id_offset_ + offset, &hdr, sizeof(hdr))) {
+      return false;
+    }
+    offset += sizeof(hdr);
+
+    if (gnu_build_id_size_ - offset < hdr.n_namesz) {
+      return false;
+    }
+    if (hdr.n_namesz > 0) {
+      std::string name(hdr.n_namesz, '\0');
+      if (!memory_->ReadFully(gnu_build_id_offset_ + offset, &(name[0]), hdr.n_namesz)) {
+        return false;
+      }
+
+      // Trim trailing \0 as GNU is stored as a C string in the ELF file.
+      if (name.back() == '\0')
+        name.resize(name.size() - 1);
+
+      // Align hdr.n_namesz to next power multiple of 4. See man 5 elf.
+      offset += (hdr.n_namesz + 3) & ~3;
+
+      if (name == "GNU" && hdr.n_type == NT_GNU_BUILD_ID) {
+        if (gnu_build_id_size_ - offset < hdr.n_descsz) {
+          return false;
+        }
+        build_id->resize(hdr.n_descsz);
+        return memory_->ReadFully(gnu_build_id_offset_ + offset, &(*build_id)[0],
+                                  hdr.n_descsz);
+      }
+    }
+    // Align hdr.n_descsz to next power multiple of 4. See man 5 elf.
+    offset += (hdr.n_descsz + 3) & ~3;
+  }
+  return false;
+}
+
 template <typename EhdrType, typename ShdrType>
 void ElfInterface::ReadSectionHeaders(const EhdrType& ehdr) {
   uint64_t offset = ehdr.e_shoff;
@@ -308,6 +358,15 @@
       // In order to read soname, keep track of address to offset mapping.
       strtabs_.push_back(std::make_pair<uint64_t, uint64_t>(static_cast<uint64_t>(shdr.sh_addr),
                                                             static_cast<uint64_t>(shdr.sh_offset)));
+    } else if (shdr.sh_type == SHT_NOTE) {
+      if (shdr.sh_name < sec_size) {
+        std::string name;
+        if (memory_->ReadString(sec_offset + shdr.sh_name, &name) &&
+            name == ".note.gnu.build-id") {
+          gnu_build_id_offset_ = shdr.sh_offset;
+          gnu_build_id_size_ = shdr.sh_size;
+        }
+      }
     }
   }
 }
@@ -492,6 +551,9 @@
 template void ElfInterface::ReadSectionHeaders<Elf32_Ehdr, Elf32_Shdr>(const Elf32_Ehdr&);
 template void ElfInterface::ReadSectionHeaders<Elf64_Ehdr, Elf64_Shdr>(const Elf64_Ehdr&);
 
+template bool ElfInterface::ReadBuildID<Elf32_Nhdr>(std::string*);
+template bool ElfInterface::ReadBuildID<Elf64_Nhdr>(std::string*);
+
 template bool ElfInterface::GetSonameWithTemplate<Elf32_Dyn>(std::string*);
 template bool ElfInterface::GetSonameWithTemplate<Elf64_Dyn>(std::string*);
 
diff --git a/libunwindstack/include/unwindstack/Elf.h b/libunwindstack/include/unwindstack/Elf.h
index e5b0a89..27f7201 100644
--- a/libunwindstack/include/unwindstack/Elf.h
+++ b/libunwindstack/include/unwindstack/Elf.h
@@ -65,6 +65,8 @@
 
   bool GetGlobalVariable(const std::string& name, uint64_t* memory_address);
 
+  bool GetBuildID(std::string* build_id);
+
   uint64_t GetRelPc(uint64_t pc, const MapInfo* map_info);
 
   bool Step(uint64_t rel_pc, uint64_t adjusted_rel_pc, Regs* regs, Memory* process_memory,
diff --git a/libunwindstack/include/unwindstack/ElfInterface.h b/libunwindstack/include/unwindstack/ElfInterface.h
index a45eba8..52992d9 100644
--- a/libunwindstack/include/unwindstack/ElfInterface.h
+++ b/libunwindstack/include/unwindstack/ElfInterface.h
@@ -62,6 +62,8 @@
 
   virtual bool GetGlobalVariable(const std::string& name, uint64_t* memory_address) = 0;
 
+  virtual bool GetBuildID(std::string* build_id) = 0;
+
   virtual bool Step(uint64_t rel_pc, Regs* regs, Memory* process_memory, bool* finished);
 
   virtual bool IsValidPc(uint64_t pc);
@@ -85,6 +87,8 @@
   uint64_t debug_frame_size() { return debug_frame_size_; }
   uint64_t gnu_debugdata_offset() { return gnu_debugdata_offset_; }
   uint64_t gnu_debugdata_size() { return gnu_debugdata_size_; }
+  uint64_t gnu_build_id_offset() { return gnu_build_id_offset_; }
+  uint64_t gnu_build_id_size() { return gnu_build_id_size_; }
 
   DwarfSection* eh_frame() { return eh_frame_.get(); }
   DwarfSection* debug_frame() { return debug_frame_.get(); }
@@ -123,6 +127,9 @@
   template <typename EhdrType>
   static void GetMaxSizeWithTemplate(Memory* memory, uint64_t* size);
 
+  template <typename NhdrType>
+  bool ReadBuildID(std::string* build_id);
+
   Memory* memory_;
   std::unordered_map<uint64_t, LoadInfo> pt_loads_;
 
@@ -143,6 +150,9 @@
   uint64_t gnu_debugdata_offset_ = 0;
   uint64_t gnu_debugdata_size_ = 0;
 
+  uint64_t gnu_build_id_offset_ = 0;
+  uint64_t gnu_build_id_size_ = 0;
+
   uint8_t soname_type_ = SONAME_UNKNOWN;
   std::string soname_;
 
@@ -182,6 +192,10 @@
     return ElfInterface::GetGlobalVariableWithTemplate<Elf32_Sym>(name, memory_address);
   }
 
+  bool GetBuildID(std::string* build_id) {
+    return ElfInterface::ReadBuildID<Elf32_Nhdr>(build_id);
+  }
+
   static void GetMaxSize(Memory* memory, uint64_t* size) {
     GetMaxSizeWithTemplate<Elf32_Ehdr>(memory, size);
   }
@@ -212,6 +226,10 @@
     return ElfInterface::GetGlobalVariableWithTemplate<Elf64_Sym>(name, memory_address);
   }
 
+  bool GetBuildID(std::string* build_id) {
+    return ElfInterface::ReadBuildID<Elf64_Nhdr>(build_id);
+  }
+
   static void GetMaxSize(Memory* memory, uint64_t* size) {
     GetMaxSizeWithTemplate<Elf64_Ehdr>(memory, size);
   }
diff --git a/libunwindstack/tests/ElfFake.h b/libunwindstack/tests/ElfFake.h
index a3bf5ce..c2bd0f6 100644
--- a/libunwindstack/tests/ElfFake.h
+++ b/libunwindstack/tests/ElfFake.h
@@ -72,6 +72,9 @@
 
   bool GetFunctionName(uint64_t, std::string*, uint64_t*) override;
   bool GetGlobalVariable(const std::string&, uint64_t*) override;
+  bool GetBuildID(std::string*) override {
+    return false;
+  }
 
   bool Step(uint64_t, Regs*, Memory*, bool*) override;
 
diff --git a/libunwindstack/tests/ElfInterfaceTest.cpp b/libunwindstack/tests/ElfInterfaceTest.cpp
index 9326bff..6023dc4 100644
--- a/libunwindstack/tests/ElfInterfaceTest.cpp
+++ b/libunwindstack/tests/ElfInterfaceTest.cpp
@@ -116,6 +116,21 @@
   void InitSym(uint64_t offset, uint32_t value, uint32_t size, uint32_t name_offset,
                uint64_t sym_offset, const char* name);
 
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildID();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDTwoNotes();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDSectionTooSmallForName();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDSectionTooSmallForDesc();
+
+  template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+  void BuildIDSectionTooSmallForHeader();
+
   MemoryFake memory_;
 };
 
@@ -898,7 +913,7 @@
 
   Ehdr ehdr = {};
   ehdr.e_shoff = offset;
-  ehdr.e_shnum = 6;
+  ehdr.e_shnum = 7;
   ehdr.e_shentsize = sizeof(Shdr);
   ehdr.e_shstrndx = 2;
   memory_.SetMemory(0, &ehdr, sizeof(ehdr));
@@ -958,10 +973,19 @@
   memory_.SetMemory(offset, &shdr, sizeof(shdr));
   offset += ehdr.e_shentsize;
 
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = 0xf00;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
   memory_.SetMemory(0xf100, ".debug_frame", sizeof(".debug_frame"));
   memory_.SetMemory(0xf200, ".gnu_debugdata", sizeof(".gnu_debugdata"));
   memory_.SetMemory(0xf300, ".eh_frame", sizeof(".eh_frame"));
   memory_.SetMemory(0xf400, ".eh_frame_hdr", sizeof(".eh_frame_hdr"));
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
 
   uint64_t load_bias = 0;
   ASSERT_TRUE(elf->Init(&load_bias));
@@ -974,6 +998,8 @@
   EXPECT_EQ(0x800U, elf->eh_frame_size());
   EXPECT_EQ(0xa000U, elf->eh_frame_hdr_offset());
   EXPECT_EQ(0xf00U, elf->eh_frame_hdr_size());
+  EXPECT_EQ(0xb000U, elf->gnu_build_id_offset());
+  EXPECT_EQ(0xf00U, elf->gnu_build_id_size());
 }
 
 TEST_F(ElfInterfaceTest, init_section_headers_offsets32) {
@@ -1153,4 +1179,321 @@
   EXPECT_FALSE(elf->IsValidPc(0x2a00));
 }
 
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildID() {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_section);
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_TRUE(elf->GetBuildID(&build_id));
+  EXPECT_STREQ(build_id.c_str(), "BUILDID");
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDTwoNotes() {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 8;  // "WRONG" aligned to 4
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "WRONG", sizeof("WRONG"));
+  note_offset += 8;
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section[note_offset], &note_header, sizeof(note_header));
+  note_offset += sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_section);
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_TRUE(elf->GetBuildID(&build_id));
+  EXPECT_STREQ(build_id.c_str(), "BUILDID");
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDSectionTooSmallForName () {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_header) + 1;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_FALSE(elf->GetBuildID(&build_id));
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDSectionTooSmallForDesc () {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_header) + sizeof("GNU") + 1;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_FALSE(elf->GetBuildID(&build_id));
+}
+
+template <typename Ehdr, typename Shdr, typename Nhdr, typename ElfInterfaceType>
+void ElfInterfaceTest::BuildIDSectionTooSmallForHeader () {
+  std::unique_ptr<ElfInterfaceType> elf(new ElfInterfaceType(&memory_));
+
+  uint64_t offset = 0x2000;
+
+  Ehdr ehdr = {};
+  ehdr.e_shoff = offset;
+  ehdr.e_shnum = 3;
+  ehdr.e_shentsize = sizeof(Shdr);
+  ehdr.e_shstrndx = 2;
+  memory_.SetMemory(0, &ehdr, sizeof(ehdr));
+
+  offset += ehdr.e_shentsize;
+
+  char note_section[128];
+  Nhdr note_header = {};
+  note_header.n_namesz = 4;  // "GNU"
+  note_header.n_descsz = 8; // "BUILDID"
+  note_header.n_type = NT_GNU_BUILD_ID;
+  memcpy(&note_section, &note_header, sizeof(note_header));
+  size_t note_offset = sizeof(note_header);
+  memcpy(&note_section[note_offset], "GNU", sizeof("GNU"));
+  note_offset += sizeof("GNU");
+  memcpy(&note_section[note_offset], "BUILDID", sizeof("BUILDID"));
+  note_offset += sizeof("BUILDID");
+
+  Shdr shdr = {};
+  shdr.sh_type = SHT_NOTE;
+  shdr.sh_name = 0x500;
+  shdr.sh_offset = 0xb000;
+  shdr.sh_size = sizeof(note_header) - 1;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  // The string data for section header names.
+  memset(&shdr, 0, sizeof(shdr));
+  shdr.sh_type = SHT_STRTAB;
+  shdr.sh_name = 0x20000;
+  shdr.sh_offset = 0xf000;
+  shdr.sh_size = 0x1000;
+  memory_.SetMemory(offset, &shdr, sizeof(shdr));
+  offset += ehdr.e_shentsize;
+
+  memory_.SetMemory(0xf500, ".note.gnu.build-id", sizeof(".note.gnu.build-id"));
+  memory_.SetMemory(0xb000, note_section, sizeof(note_section));
+
+  uint64_t load_bias = 0;
+  ASSERT_TRUE(elf->Init(&load_bias));
+  std::string build_id;
+  ASSERT_FALSE(elf->GetBuildID(&build_id));
+}
+
+TEST_F(ElfInterfaceTest, build_id32) {
+  BuildID<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id64) {
+  BuildID<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_two_notes32) {
+  BuildIDTwoNotes<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_two_notes64) {
+  BuildIDTwoNotes<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_name32) {
+  BuildIDSectionTooSmallForName<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_name64) {
+  BuildIDSectionTooSmallForName<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_desc32) {
+  BuildIDSectionTooSmallForDesc<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_desc64) {
+  BuildIDSectionTooSmallForDesc<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_header32) {
+  BuildIDSectionTooSmallForHeader<Elf32_Ehdr, Elf32_Shdr, Elf32_Nhdr, ElfInterface32>();
+}
+
+TEST_F(ElfInterfaceTest, build_id_section_too_small_for_header64) {
+  BuildIDSectionTooSmallForHeader<Elf64_Ehdr, Elf64_Shdr, Elf64_Nhdr, ElfInterface64>();
+}
+
 }  // namespace unwindstack
diff --git a/libunwindstack/tests/ElfTest.cpp b/libunwindstack/tests/ElfTest.cpp
index ccf8927..7766218 100644
--- a/libunwindstack/tests/ElfTest.cpp
+++ b/libunwindstack/tests/ElfTest.cpp
@@ -311,6 +311,7 @@
   void InitHeaders(uint64_t) override {}
   bool GetSoname(std::string*) override { return false; }
   bool GetFunctionName(uint64_t, std::string*, uint64_t*) override { return false; }
+  bool GetBuildID(std::string*) override { return false; }
 
   MOCK_METHOD4(Step, bool(uint64_t, Regs*, Memory*, bool*));
   MOCK_METHOD2(GetGlobalVariable, bool(const std::string&, uint64_t*));
diff --git a/libunwindstack/tools/unwind_info.cpp b/libunwindstack/tools/unwind_info.cpp
index aebeb95..3f2dfb0 100644
--- a/libunwindstack/tools/unwind_info.cpp
+++ b/libunwindstack/tools/unwind_info.cpp
@@ -123,6 +123,15 @@
     printf("Soname: %s\n", soname.c_str());
   }
 
+  std::string build_id;
+  if (elf.GetBuildID(&build_id)) {
+    printf("Build ID: ");
+    for (size_t i = 0; i < build_id.size(); ++i) {
+      printf("%02hhx", build_id[i]);
+    }
+    printf("\n");
+  }
+
   ElfInterface* interface = elf.interface();
   if (elf.machine_type() == EM_ARM) {
     DumpArm(&elf, reinterpret_cast<ElfInterfaceArm*>(interface));
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index aad00ad..f88f6b9 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -9,6 +9,10 @@
 LOCAL_MODULE_CLASS := ETC
 LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT)
 
+# The init symlink must be a post install command of a file that is to TARGET_ROOT_OUT.
+# Since init.rc is required for init and satisfies that requirement, we hijack it to create the symlink.
+LOCAL_POST_INSTALL_CMD := ln -sf /system/bin/init $(TARGET_ROOT_OUT)/init
+
 include $(BUILD_PREBUILT)
 
 #######################################
diff --git a/shell_and_utilities/README.md b/shell_and_utilities/README.md
index d8cf867..ffda3a5 100644
--- a/shell_and_utilities/README.md
+++ b/shell_and_utilities/README.md
@@ -1,5 +1,4 @@
-Android's shell and utilities
-=============================
+# Android's shell and utilities
 
 Since IceCreamSandwich Android has used
 [mksh](https://www.mirbsd.org/mksh.htm) as its shell. Before then it used
@@ -34,8 +33,7 @@
 full list for a release by running `toybox` directly.
 
 
-Android 2.3 (Gingerbread)
--------------------------
+## Android 2.3 (Gingerbread)
 
 BSD: cat dd newfs\_msdos
 
@@ -46,8 +44,7 @@
 umount uptime vmstat watchprops wipe
 
 
-Android 4.0 (IceCreamSandwich)
-------------------------------
+## Android 4.0 (IceCreamSandwich)
 
 BSD: cat dd newfs\_msdos
 
@@ -58,8 +55,7 @@
 touch umount uptime vmstat watchprops wipe
 
 
-Android 4.1-4.3 (JellyBean)
----------------------------
+## Android 4.1-4.3 (JellyBean)
 
 BSD: cat cp dd du grep newfs\_msdos
 
@@ -71,8 +67,7 @@
 sync top touch umount uptime vmstat watchprops wipe
 
 
-Android 4.4 (KitKat)
---------------------
+## Android 4.4 (KitKat)
 
 BSD: cat cp dd du grep newfs\_msdos
 
@@ -84,8 +79,7 @@
 stop swapoff swapon sync top touch umount uptime vmstat watchprops wipe
 
 
-Android 5.0 (Lollipop)
-----------------------
+## Android 5.0 (Lollipop)
 
 BSD: cat chown cp dd du grep kill ln mv printenv rm rmdir sleep sync
 
@@ -97,8 +91,7 @@
 top touch umount uptime vmstat watchprops wipe
 
 
-Android 6.0 (Marshmallow)
--------------------------
+## Android 6.0 (Marshmallow)
 
 BSD: dd du grep
 
@@ -118,8 +111,7 @@
 vmstat wc which whoami xargs yes
 
 
-Android 7.0 (Nougat)
---------------------
+## Android 7.0 (Nougat)
 
 BSD: dd grep
 
@@ -140,8 +132,7 @@
 uptime usleep vmstat wc which whoami xargs xxd yes
 
 
-Android 8.0 (Oreo)
-------------------
+## Android 8.0 (Oreo)
 
 BSD: dd grep
 
@@ -164,8 +155,8 @@
 tty ulimit umount uname uniq unix2dos uptime usleep uudecode uuencode
 vmstat wc which whoami xargs xxd yes zcat
 
-Android P
----------
+
+## Android 9.0 (Pie)
 
 BSD: dd grep
 
@@ -190,8 +181,8 @@
 umount uname uniq unix2dos uptime usleep uudecode uuencode vmstat wc
 which whoami xargs xxd yes zcat
 
-Android Q
----------
+
+## Android Q
 
 BSD: grep fsck\_msdos newfs\_msdos
 
@@ -201,17 +192,22 @@
 
 toolbox: getevent getprop
 
-toybox: acpi base64 basename blockdev cal cat chcon chgrp chmod chown
-chroot chrt cksum clear cmp comm cp cpio cut date dd df diff dirname
-dmesg dos2unix du echo env expand expr fallocate false file find flock
-fmt free getenforce groups gunzip gzip head hostname hwclock id ifconfig
-inotifyd insmod ionice iorenice kill killall ln load\_policy log logname
-losetup ls lsmod lsof lspci lsusb md5sum microcom mkdir mkfifo mknod
-mkswap mktemp modinfo modprobe more mount mountpoint mv nc netcat netstat
-nice nl nohup nsenter od paste patch pgrep pidof pkill pmap printenv
-printf ps pwd readlink realpath renice restorecon rm rmdir rmmod runcon
-sed sendevent seq setenforce setprop setsid sha1sum sha224sum sha256sum
-sha384sum sha512sum sleep sort split start stat stop strings stty swapoff
-swapon sync sysctl tac tail tar taskset tee time timeout top touch tr
-true truncate tty ulimit umount uname uniq unix2dos unshare uptime usleep
-uudecode uuencode vmstat wc which whoami xargs xxd yes zcat
+toybox: acpi base64 basename bc blkid blockdev cal cat chattr chcon chgrp
+chmod chown chroot chrt cksum clear cmp comm cp cpio cut date dd df
+diff dirname dmesg dos2unix du echo egrep env expand expr fallocate
+false fgrep file find flock fmt free freeramdisk fsfreeze getconf
+getenforce getfattr grep groups gunzip gzip head help hostname hwclock
+i2cdetect i2cdump i2cget i2cset iconv id ifconfig inotifyd insmod
+install ionice iorenice iotop kill killall ln load\_policy log logname
+losetup ls lsattr lsmod lsof lspci lsusb makedevs md5sum microcom
+mkdir mkfifo mknod mkswap mktemp modinfo modprobe more mount mountpoint
+mv nbd-client nc netcat netstat nice nl nohup nproc nsenter od partprobe
+paste patch pgrep pidof ping ping6 pivot\_root pkill pmap printenv
+printf prlimit ps pwd pwdx readlink realpath renice restorecon rev
+rfkill rm rmdir rmmod runcon sed sendevent seq setenforce setfattr
+setprop setsid sha1sum sha224sum sha256sum sha384sum sha512sum sleep
+sort split start stat stop strings stty swapoff swapon sync sysctl
+tac tail tar taskset tee time timeout top touch tr traceroute traceroute6
+true truncate tty tunctl ulimit umount uname uniq unix2dos unlink
+unshare uptime usleep uudecode uuencode uuidgen vconfig vmstat watch
+wc which whoami xargs xxd yes zcat