Fix offsets when shared lib split across maps.
The linker was modified so that a shared library has a read-only
map, then a read-execute map to represent the whole shared library.
When backtraces are created, then the offsets are set incorrectly
for backtraces. For example, all backtraces wind up with an offset now,
and a shared library loaded out of an apk shows the wrong offset.
Changes:
- Fix the FormatFrame function which was putting the offset before the
map name.
- Refactor the Maps and MapInfo classes to keep track of the previous map
instead of all maps. This was the only map that was ever needed.
- Modify the unwind_for_offline tool to capture both the read-only and
read-execute map when using the read-only segment option.
Bug: 120981155
Test: Updated unit tests pass.
Test: Unwinds on device don't show the offsets everywhere any more.
Change-Id: I75b3727221be9c20316dfdcd7a1c6d242d7ce948
diff --git a/libunwindstack/MapInfo.cpp b/libunwindstack/MapInfo.cpp
index 44ec5c1..39a09cf 100644
--- a/libunwindstack/MapInfo.cpp
+++ b/libunwindstack/MapInfo.cpp
@@ -32,33 +32,27 @@
bool MapInfo::InitFileMemoryFromPreviousReadOnlyMap(MemoryFileAtOffset* memory) {
// One last attempt, see if the previous map is read-only with the
// same name and stretches across this map.
- for (auto iter = maps_->begin(); iter != maps_->end(); ++iter) {
- if (*iter == this) {
- if (iter == maps_->begin()) {
- return false;
- }
- --iter;
- MapInfo* prev_map = *iter;
- // Make sure this is a read-only map.
- if (prev_map->flags != PROT_READ) {
- return false;
- }
- uint64_t map_size = end - prev_map->end;
- if (!memory->Init(name, prev_map->offset, map_size)) {
- return false;
- }
- uint64_t max_size;
- if (!Elf::GetInfo(memory, &max_size) || max_size < map_size) {
- return false;
- }
- if (!memory->Init(name, prev_map->offset, max_size)) {
- return false;
- }
- elf_offset = offset - prev_map->offset;
- return true;
- }
+ if (prev_map == nullptr || prev_map->flags != PROT_READ) {
+ return false;
}
- return false;
+
+ uint64_t map_size = end - prev_map->end;
+ if (!memory->Init(name, prev_map->offset, map_size)) {
+ return false;
+ }
+
+ uint64_t max_size;
+ if (!Elf::GetInfo(memory, &max_size) || max_size < map_size) {
+ return false;
+ }
+
+ if (!memory->Init(name, prev_map->offset, max_size)) {
+ return false;
+ }
+
+ elf_offset = offset - prev_map->offset;
+ elf_start_offset = prev_map->offset;
+ return true;
}
Memory* MapInfo::GetFileMemory() {
@@ -91,14 +85,13 @@
// Check if the start of this map is an embedded elf.
uint64_t max_size = 0;
- uint64_t file_offset = offset;
if (Elf::GetInfo(memory.get(), &max_size)) {
if (max_size > map_size) {
- if (memory->Init(name, file_offset, max_size)) {
+ if (memory->Init(name, offset, max_size)) {
return memory.release();
}
// Try to reinit using the default map_size.
- if (memory->Init(name, file_offset, map_size)) {
+ if (memory->Init(name, offset, map_size)) {
return memory.release();
}
return nullptr;
@@ -109,6 +102,13 @@
// No elf at offset, try to init as if the whole file is an elf.
if (memory->Init(name, 0) && Elf::IsValidElf(memory.get())) {
elf_offset = offset;
+ // Need to check how to set the elf start offset. If this map is not
+ // the r-x map of a r-- map, then use the real offset value. Otherwise,
+ // use 0.
+ if (prev_map == nullptr || prev_map->offset != 0 || prev_map->flags != PROT_READ ||
+ prev_map->name != name) {
+ elf_start_offset = offset;
+ }
return memory.release();
}
@@ -156,35 +156,24 @@
return memory.release();
}
- if (name.empty() || maps_ == nullptr) {
- return nullptr;
- }
-
// Find the read-only map by looking at the previous map. The linker
// doesn't guarantee that this invariant will always be true. However,
// if that changes, there is likely something else that will change and
// break something.
- MapInfo* ro_map_info = nullptr;
- for (auto iter = maps_->begin(); iter != maps_->end(); ++iter) {
- if (*iter == this) {
- if (iter != maps_->begin()) {
- --iter;
- ro_map_info = *iter;
- }
- break;
- }
- }
-
- if (ro_map_info == nullptr || ro_map_info->name != name || ro_map_info->offset >= offset) {
+ if (offset == 0 || name.empty() || prev_map == nullptr || prev_map->name != name ||
+ prev_map->offset >= offset) {
return nullptr;
}
// Make sure that relative pc values are corrected properly.
- elf_offset = offset - ro_map_info->offset;
+ elf_offset = offset - prev_map->offset;
+ // Use this as the elf start offset, otherwise, you always get offsets into
+ // the r-x section, which is not quite the right information.
+ elf_start_offset = prev_map->offset;
MemoryRanges* ranges = new MemoryRanges;
- ranges->Insert(new MemoryRange(process_memory, ro_map_info->start,
- ro_map_info->end - ro_map_info->start, 0));
+ ranges->Insert(
+ new MemoryRange(process_memory, prev_map->start, prev_map->end - prev_map->start, 0));
ranges->Insert(new MemoryRange(process_memory, start, end - start, elf_offset));
return ranges;