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

1 files changed, 46 insertions, 0 deletions

diff --git a/libunwindstack/tests/MapInfoCreateMemoryTest.cpp b/libunwindstack/tests/MapInfoCreateMemoryTest.cpp
index 943b3c9dc..a66685a26 100644
--- a/libunwindstack/tests/MapInfoCreateMemoryTest.cpp
+++ b/libunwindstack/tests/MapInfoCreateMemoryTest.cpp
@@ -118,6 +118,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_full_file) {
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
   ASSERT_EQ(0x100U, info.elf_offset);
+  EXPECT_EQ(0x100U, info.elf_start_offset);
 
   // Read the entire file.
   std::vector<uint8_t> buffer(1024);
@@ -129,6 +130,44 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_full_file) {
   }
 
   ASSERT_FALSE(memory->ReadFully(1024, buffer.data(), 1));
+
+  // Now verify the elf start offset is set correctly based on the previous
+  // info.
+  MapInfo prev_info(nullptr, 0, 0x100, 0x10, 0, "");
+  info.prev_map = &prev_info;
+
+  // No preconditions met, change each one until it should set the elf start
+  // offset to zero.
+  info.elf_offset = 0;
+  info.elf_start_offset = 0;
+  memory.reset(info.CreateMemory(process_memory_));
+  ASSERT_TRUE(memory.get() != nullptr);
+  ASSERT_EQ(0x100U, info.elf_offset);
+  EXPECT_EQ(0x100U, info.elf_start_offset);
+
+  prev_info.offset = 0;
+  info.elf_offset = 0;
+  info.elf_start_offset = 0;
+  memory.reset(info.CreateMemory(process_memory_));
+  ASSERT_TRUE(memory.get() != nullptr);
+  ASSERT_EQ(0x100U, info.elf_offset);
+  EXPECT_EQ(0x100U, info.elf_start_offset);
+
+  prev_info.flags = PROT_READ;
+  info.elf_offset = 0;
+  info.elf_start_offset = 0;
+  memory.reset(info.CreateMemory(process_memory_));
+  ASSERT_TRUE(memory.get() != nullptr);
+  ASSERT_EQ(0x100U, info.elf_offset);
+  EXPECT_EQ(0x100U, info.elf_start_offset);
+
+  prev_info.name = info.name;
+  info.elf_offset = 0;
+  info.elf_start_offset = 0;
+  memory.reset(info.CreateMemory(process_memory_));
+  ASSERT_TRUE(memory.get() != nullptr);
+  ASSERT_EQ(0x100U, info.elf_offset);
+  EXPECT_EQ(0U, info.elf_start_offset);
 }
 
 // Verify that if the offset is non-zero and there is an elf at that
@@ -139,6 +178,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file) {
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
   ASSERT_EQ(0U, info.elf_offset);
+  EXPECT_EQ(0U, info.elf_start_offset);
 
   // Read the valid part of the file.
   std::vector<uint8_t> buffer(0x100);
@@ -162,6 +202,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file_whole_e
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
   ASSERT_EQ(0U, info.elf_offset);
+  EXPECT_EQ(0U, info.elf_start_offset);
 
   // Verify the memory is a valid elf.
   uint8_t e_ident[SELFMAG + 1];
@@ -178,6 +219,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file_whole_e
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
   ASSERT_EQ(0U, info.elf_offset);
+  EXPECT_EQ(0U, info.elf_start_offset);
 
   // Verify the memory is a valid elf.
   uint8_t e_ident[SELFMAG + 1];
@@ -250,6 +292,7 @@ TEST_F(MapInfoCreateMemoryTest, valid_rosegment_zero_offset) {
   ASSERT_TRUE(mem.get() != nullptr);
   EXPECT_EQ(0x4000UL, map_info->elf_offset);
   EXPECT_EQ(0x4000UL, map_info->offset);
+  EXPECT_EQ(0U, map_info->elf_start_offset);
 
   // Verify that reading values from this memory works properly.
   std::vector<uint8_t> buffer(0x4000);
@@ -295,6 +338,7 @@ TEST_F(MapInfoCreateMemoryTest, valid_rosegment_non_zero_offset) {
   ASSERT_TRUE(mem.get() != nullptr);
   EXPECT_EQ(0x1000UL, map_info->elf_offset);
   EXPECT_EQ(0xb000UL, map_info->offset);
+  EXPECT_EQ(0xa000UL, map_info->elf_start_offset);
 
   // Verify that reading values from this memory works properly.
   std::vector<uint8_t> buffer(0x4000);
@@ -333,6 +377,7 @@ TEST_F(MapInfoCreateMemoryTest, rosegment_from_file) {
   std::vector<uint8_t> buffer(0x100);
   EXPECT_EQ(0x2000U, map_info->offset);
   EXPECT_EQ(0U, map_info->elf_offset);
+  EXPECT_EQ(0U, map_info->elf_start_offset);
   ASSERT_TRUE(memory->ReadFully(0, buffer.data(), 0x100));
   EXPECT_EQ(0xffU, buffer[0]);
 
@@ -346,6 +391,7 @@ TEST_F(MapInfoCreateMemoryTest, rosegment_from_file) {
   memory.reset(map_info->CreateMemory(process_memory_));
   EXPECT_EQ(0x2000U, map_info->offset);
   EXPECT_EQ(0x1000U, map_info->elf_offset);
+  EXPECT_EQ(0x1000U, map_info->elf_start_offset);
   Elf64_Ehdr ehdr_mem;
   ASSERT_TRUE(memory->ReadFully(0, &ehdr_mem, sizeof(ehdr_mem)));
   EXPECT_TRUE(memcmp(&ehdr, &ehdr_mem, sizeof(ehdr)) == 0);