diff --git a/libc/async_safe/async_safe_log.cpp b/libc/async_safe/async_safe_log.cpp
index 420560f..2bff616 100644
--- a/libc/async_safe/async_safe_log.cpp
+++ b/libc/async_safe/async_safe_log.cpp
@@ -207,10 +207,12 @@
   // Decode the conversion specifier.
   int is_signed = (conversion == 'd' || conversion == 'i' || conversion == 'o');
   int base = 10;
-  if (conversion == 'x' || conversion == 'X') {
+  if (tolower(conversion) == 'x') {
     base = 16;
   } else if (conversion == 'o') {
     base = 8;
+  } else if (tolower(conversion) == 'b') {
+    base = 2;
   }
   bool caps = (conversion == 'X');
 
@@ -360,7 +362,8 @@
       format_integer(buffer + 2, sizeof(buffer) - 2, value, 'x');
     } else if (c == 'm') {
       strerror_r(errno, buffer, sizeof(buffer));
-    } else if (c == 'd' || c == 'i' || c == 'o' || c == 'u' || c == 'x' || c == 'X') {
+    } else if (tolower(c) == 'b' || c == 'd' || c == 'i' || c == 'o' || c == 'u' ||
+               tolower(c) == 'x') {
       /* integers - first read value from stack */
       uint64_t value;
       int is_signed = (c == 'd' || c == 'i' || c == 'o');
@@ -391,10 +394,10 @@
         value = static_cast<uint64_t>((static_cast<int64_t>(value << shift)) >> shift);
       }
 
-      if (alternate && value != 0 && (c == 'x' || c == 'o')) {
-        if (c == 'x') {
+      if (alternate && value != 0 && (tolower(c) == 'x' || c == 'o' || tolower(c) == 'b')) {
+        if (tolower(c) == 'x' || tolower(c) == 'b') {
           buffer[0] = '0';
-          buffer[1] = 'x';
+          buffer[1] = c;
           format_integer(buffer + 2, sizeof(buffer) - 2, value, c);
         } else {
           buffer[0] = '0';
diff --git a/libc/bionic/sysconf.cpp b/libc/bionic/sysconf.cpp
index 3906e2e..edbdef1 100644
--- a/libc/bionic/sysconf.cpp
+++ b/libc/bionic/sysconf.cpp
@@ -41,6 +41,107 @@
 #include "platform/bionic/page.h"
 #include "private/bionic_tls.h"
 
+struct sysconf_cache {
+  long size, assoc, linesize;
+
+  static sysconf_cache from_size_and_geometry(int size_id, int geometry_id) {
+    sysconf_cache result;
+    result.size = getauxval(size_id);
+    unsigned long geometry = getauxval(geometry_id);
+    result.assoc = geometry >> 16;
+    result.linesize = geometry & 0xffff;
+    return result;
+  }
+};
+
+struct sysconf_caches {
+  sysconf_cache l1_i, l1_d, l2, l3, l4;
+};
+
+#if defined(__riscv)
+
+static sysconf_caches* __sysconf_caches() {
+  static sysconf_caches cached = []{
+    sysconf_caches info = {};
+    // riscv64 kernels conveniently hand us all this information.
+    info.l1_i = sysconf_cache::from_size_and_geometry(AT_L1I_CACHESIZE, AT_L1I_CACHEGEOMETRY);
+    info.l1_d = sysconf_cache::from_size_and_geometry(AT_L1D_CACHESIZE, AT_L1D_CACHEGEOMETRY);
+    info.l2 = sysconf_cache::from_size_and_geometry(AT_L2_CACHESIZE, AT_L2_CACHEGEOMETRY);
+    info.l3 = sysconf_cache::from_size_and_geometry(AT_L3_CACHESIZE, AT_L3_CACHEGEOMETRY);
+    return info;
+  }();
+  return &cached;
+}
+
+#elif defined(__aarch64__)
+
+static sysconf_caches* __sysconf_caches() {
+  static sysconf_caches cached = []{
+    sysconf_caches info = {};
+    // arm64 is especially limited. We can infer the L1 line sizes, but that's it.
+    uint64_t ctr_el0;
+    __asm__ __volatile__("mrs %0, ctr_el0" : "=r"(ctr_el0));
+    info.l1_i.linesize = 4 << (ctr_el0 & 0xf);
+    info.l1_d.linesize = 4 << ((ctr_el0 >> 16) & 0xf);
+    return info;
+  }();
+  return &cached;
+}
+
+#else
+
+long __sysconf_fread_long(const char* path) {
+  long result = 0;
+  FILE* fp = fopen(path, "re");
+  if (fp != nullptr) {
+    fscanf(fp, "%ld", &result);
+    fclose(fp);
+  }
+  return result;
+}
+
+static sysconf_caches* __sysconf_caches() {
+  static sysconf_caches cached = []{
+    sysconf_caches info = {};
+    char path[64];
+    for (int i = 0; i < 4; i++) {
+      sysconf_cache c;
+
+      snprintf(path, sizeof(path), "/sys/devices/system/cpu/cpu0/cache/index%d/size", i);
+      c.size = __sysconf_fread_long(path) * 1024;
+      if (c.size == 0) break;
+
+      snprintf(path, sizeof(path), "/sys/devices/system/cpu/cpu0/cache/index%d/ways_of_associativity", i);
+      c.assoc = __sysconf_fread_long(path);
+
+      snprintf(path, sizeof(path), "/sys/devices/system/cpu/cpu0/cache/index%d/coherency_line_size", i);
+      c.linesize = __sysconf_fread_long(path);
+
+      snprintf(path, sizeof(path), "/sys/devices/system/cpu/cpu0/cache/index%d/level", i);
+      int level = __sysconf_fread_long(path);
+      if (level == 1) {
+        snprintf(path, sizeof(path), "/sys/devices/system/cpu/cpu0/cache/index%d/type", i);
+        FILE* fp = fopen(path, "re");
+        char type = fgetc(fp);
+        fclose(fp);
+        if (type == 'D') {
+          info.l1_d = c;
+        } else if (type == 'I') {
+          info.l1_i = c;
+        }
+      } else if (level == 2) {
+        info.l2 = c;
+      } else if (level == 3) {
+        info.l3 = c;
+      }
+    }
+    return info;
+  }();
+  return &cached;
+}
+
+#endif
+
 static long __sysconf_rlimit(int resource) {
   rlimit rl;
   getrlimit(resource, &rl);
@@ -218,23 +319,21 @@
     case _SC_XOPEN_STREAMS:     return -1;            // Obsolescent in POSIX.1-2008.
     case _SC_XOPEN_UUCP:        return -1;
 
-    // We do not have actual implementations for cache queries.
-    // It's valid to return 0 as the result is unknown.
-    case _SC_LEVEL1_ICACHE_SIZE:      return 0;
-    case _SC_LEVEL1_ICACHE_ASSOC:     return 0;
-    case _SC_LEVEL1_ICACHE_LINESIZE:  return 0;
-    case _SC_LEVEL1_DCACHE_SIZE:      return 0;
-    case _SC_LEVEL1_DCACHE_ASSOC:     return 0;
-    case _SC_LEVEL1_DCACHE_LINESIZE:  return 0;
-    case _SC_LEVEL2_CACHE_SIZE:       return 0;
-    case _SC_LEVEL2_CACHE_ASSOC:      return 0;
-    case _SC_LEVEL2_CACHE_LINESIZE:   return 0;
-    case _SC_LEVEL3_CACHE_SIZE:       return 0;
-    case _SC_LEVEL3_CACHE_ASSOC:      return 0;
-    case _SC_LEVEL3_CACHE_LINESIZE:   return 0;
-    case _SC_LEVEL4_CACHE_SIZE:       return 0;
-    case _SC_LEVEL4_CACHE_ASSOC:      return 0;
-    case _SC_LEVEL4_CACHE_LINESIZE:   return 0;
+    case _SC_LEVEL1_ICACHE_SIZE:      return __sysconf_caches()->l1_i.size;
+    case _SC_LEVEL1_ICACHE_ASSOC:     return __sysconf_caches()->l1_i.assoc;
+    case _SC_LEVEL1_ICACHE_LINESIZE:  return __sysconf_caches()->l1_i.linesize;
+    case _SC_LEVEL1_DCACHE_SIZE:      return __sysconf_caches()->l1_d.size;
+    case _SC_LEVEL1_DCACHE_ASSOC:     return __sysconf_caches()->l1_d.assoc;
+    case _SC_LEVEL1_DCACHE_LINESIZE:  return __sysconf_caches()->l1_d.linesize;
+    case _SC_LEVEL2_CACHE_SIZE:       return __sysconf_caches()->l2.size;
+    case _SC_LEVEL2_CACHE_ASSOC:      return __sysconf_caches()->l2.assoc;
+    case _SC_LEVEL2_CACHE_LINESIZE:   return __sysconf_caches()->l2.linesize;
+    case _SC_LEVEL3_CACHE_SIZE:       return __sysconf_caches()->l3.size;
+    case _SC_LEVEL3_CACHE_ASSOC:      return __sysconf_caches()->l3.assoc;
+    case _SC_LEVEL3_CACHE_LINESIZE:   return __sysconf_caches()->l3.linesize;
+    case _SC_LEVEL4_CACHE_SIZE:       return __sysconf_caches()->l4.size;
+    case _SC_LEVEL4_CACHE_ASSOC:      return __sysconf_caches()->l4.assoc;
+    case _SC_LEVEL4_CACHE_LINESIZE:   return __sysconf_caches()->l4.linesize;
 
     default:
       errno = EINVAL;
diff --git a/tests/async_safe_test.cpp b/tests/async_safe_test.cpp
index dc4db07..cc1b598 100644
--- a/tests/async_safe_test.cpp
+++ b/tests/async_safe_test.cpp
@@ -45,6 +45,15 @@
   async_safe_format_buffer(buf, sizeof(buf), "aa%scc", "bb");
   EXPECT_STREQ("aabbcc", buf);
 
+  async_safe_format_buffer(buf, sizeof(buf), "a%bb", 1234);
+  EXPECT_STREQ("a10011010010b", buf);
+
+  async_safe_format_buffer(buf, sizeof(buf), "a%#bb", 1234);
+  EXPECT_STREQ("a0b10011010010b", buf);
+
+  async_safe_format_buffer(buf, sizeof(buf), "a%#Bb", 1234);
+  EXPECT_STREQ("a0B10011010010b", buf);
+
   async_safe_format_buffer(buf, sizeof(buf), "a%cc", 'b');
   EXPECT_STREQ("abc", buf);
 
@@ -76,9 +85,15 @@
   async_safe_format_buffer(buf, sizeof(buf), "a%xz", 0x12ab);
   EXPECT_STREQ("a12abz", buf);
 
+  async_safe_format_buffer(buf, sizeof(buf), "a%#xz", 0x12ab);
+  EXPECT_STREQ("a0x12abz", buf);
+
   async_safe_format_buffer(buf, sizeof(buf), "a%Xz", 0x12ab);
   EXPECT_STREQ("a12ABz", buf);
 
+  async_safe_format_buffer(buf, sizeof(buf), "a%#Xz", 0x12ab);
+  EXPECT_STREQ("a0X12ABz", buf);
+
   async_safe_format_buffer(buf, sizeof(buf), "a%08xz", 0x123456);
   EXPECT_STREQ("a00123456z", buf);
 
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 4c21627..b639a4e 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -1166,6 +1166,26 @@
   VERIFY_SYSCONF_UNKNOWN(666);
 }
 
+static void show_cache(const char* name, long size, long assoc, long line_size) {
+  printf("%s cache size: %ld bytes, line size %ld bytes, ", name, size, line_size);
+  if (assoc == 0) {
+    printf("fully");
+  } else {
+    printf("%ld-way", assoc);
+  }
+  printf(" associative\n");
+}
+
+TEST(UNISTD_TEST, sysconf_cache) {
+  // It's not obvious we can _test_ any of these, but we can at least
+  // show the output for humans to inspect.
+  show_cache("L1D", sysconf(_SC_LEVEL1_DCACHE_SIZE), sysconf(_SC_LEVEL1_DCACHE_ASSOC), sysconf(_SC_LEVEL1_DCACHE_LINESIZE));
+  show_cache("L1I", sysconf(_SC_LEVEL1_ICACHE_SIZE), sysconf(_SC_LEVEL1_ICACHE_ASSOC), sysconf(_SC_LEVEL1_ICACHE_LINESIZE));
+  show_cache("L2", sysconf(_SC_LEVEL2_CACHE_SIZE), sysconf(_SC_LEVEL2_CACHE_ASSOC), sysconf(_SC_LEVEL2_CACHE_LINESIZE));
+  show_cache("L3", sysconf(_SC_LEVEL3_CACHE_SIZE), sysconf(_SC_LEVEL3_CACHE_ASSOC), sysconf(_SC_LEVEL3_CACHE_LINESIZE));
+  show_cache("L4", sysconf(_SC_LEVEL4_CACHE_SIZE), sysconf(_SC_LEVEL4_CACHE_ASSOC), sysconf(_SC_LEVEL4_CACHE_LINESIZE));
+}
+
 TEST(UNISTD_TEST, dup2_same) {
   // POSIX says of dup2:
   // If fildes2 is already a valid open file descriptor ...