Demand read load bias for a map.

Add a static GetLoadBias method to the Elf object that only reads just
enough to get the load bias.

Add a method to MapInfo that gets the load bias. First attempt to get
it if the elf object already exists. If no elf object was created, use
the new static method to get the load bias.

In BacktraceMap, add a custom iterator so that when code dereferences
a map element, that's when the load bias will be retrieved if it hasn't
already been set.

Bug: 69871050

Test: New unit tests, verify tombstones have non-zero load bias values for
Test: libraries with a non-zero load bias.
Change-Id: I125f4abc827589957fce2f0df24b0f25d037d732

1 files changed, 23 insertions, 0 deletions

diff --git a/libunwindstack/ElfInterface.cpp b/libunwindstack/ElfInterface.cpp
index 9bdb094..334cf76 100644
--- a/libunwindstack/ElfInterface.cpp
+++ b/libunwindstack/ElfInterface.cpp
@@ -148,6 +148,26 @@ bool ElfInterface::ReadAllHeaders(uint64_t* load_bias) {
 }
 
 template <typename EhdrType, typename PhdrType>
+uint64_t ElfInterface::GetLoadBias(Memory* memory) {
+  EhdrType ehdr;
+  if (!memory->Read(0, &ehdr, sizeof(ehdr))) {
+    return false;
+  }
+
+  uint64_t offset = ehdr.e_phoff;
+  for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
+    PhdrType phdr;
+    if (!memory->Read(offset, &phdr, sizeof(phdr))) {
+      return 0;
+    }
+    if (phdr.p_type == PT_LOAD && phdr.p_offset == 0) {
+      return phdr.p_vaddr;
+    }
+  }
+  return 0;
+}
+
+template <typename EhdrType, typename PhdrType>
 bool ElfInterface::ReadProgramHeaders(const EhdrType& ehdr, uint64_t* load_bias) {
   uint64_t offset = ehdr.e_phoff;
   for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
@@ -421,4 +441,7 @@ template bool ElfInterface::GetFunctionNameWithTemplate<Elf64_Sym>(uint64_t, uin
 template void ElfInterface::GetMaxSizeWithTemplate<Elf32_Ehdr>(Memory*, uint64_t*);
 template void ElfInterface::GetMaxSizeWithTemplate<Elf64_Ehdr>(Memory*, uint64_t*);
 
+template uint64_t ElfInterface::GetLoadBias<Elf32_Ehdr, Elf32_Phdr>(Memory*);
+template uint64_t ElfInterface::GetLoadBias<Elf64_Ehdr, Elf64_Phdr>(Memory*);
+
 }  // namespace unwindstack