Support kernel modules for text profiles

addr2line.cc

@@ -26,6 +26,7 @@
 #include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
 #include "llvm/Object/Binary.h"
 #include "llvm/Object/ObjectFile.h"
+#include "llvm/Support/Error.h"
 
 ABSL_RETIRED_FLAG(bool, use_legacy_symbolizer, false,
                   "whether to use google3 symbolizer");
@@ -87,8 +88,29 @@ void LLVMAddr2line::GetInlineStack(uint64_t address, SourceStack *stack) const {
   llvm::SmallVector<llvm::DWARFDie, 4> InlinedChain;
   cu_iter->second->getInlinedChainForAddress(address, InlinedChain);
 
-  uint32_t row_index = line_table->lookupAddress(
-      {address, llvm::object::SectionedAddress::UndefSection});
+  uint64_t section_index = llvm::object::SectionedAddress::UndefSection;
+  if (IsKernelModule(getObject()->getFileName())) {
+    // For kernel modules (relocatable objects), line table sequences are often
+    // tied to their actual section. We must provide the actual section index
+    // (instead of the UndefSection wildcard) to lookupAddress, otherwise it
+    // will fail to match sequences that are not marked as UndefSection. We
+    // only focus on the .text section to be consistent with symbol_map.cc.
+    for (const auto& sec : getObject()->sections()) {
+      auto name = sec.getName();
+      if (!name) {
+        llvm::consumeError(name.takeError());
+        continue;
+      }
+      if (*name == ".text") {
+        if (address >= sec.getAddress() &&
+            address < sec.getAddress() + sec.getSize()) {
+          section_index = sec.getIndex();
+        }
+        break;
+      }
+    }
+  }
+  uint32_t row_index = line_table->lookupAddress({address, section_index});
   uint32_t file = (row_index == -1U ? -1U : line_table->Rows[row_index].File);
   uint32_t line = (row_index == -1U ? 0 : line_table->Rows[row_index].Line);
   uint32_t discriminator =

addr2line.h

@@ -13,6 +13,7 @@
 
 #include "base/integral_types.h"
 #include "source_info.h"
+#include "third_party/abseil/absl/strings/match.h"
 #include "third_party/abseil/absl/strings/string_view.h"
 
 #if defined(HAVE_LLVM)
@@ -89,6 +90,11 @@ class Google3Addr2line : public Addr2line {
   DISALLOW_COPY_AND_ASSIGN(Google3Addr2line);
 };
 #endif
+
+inline bool IsKernelModule(absl::string_view path) {
+  return absl::EndsWith(path, ".ko");
+}
+
 }  // namespace devtools_crosstool_autofdo
 
 #endif  // AUTOFDO_ADDR2LINE_H_

symbol_map.cc

@@ -478,6 +478,18 @@ void SymbolMap::ReadLoadableExecSegmentInfo(bool is_kernel) {
                 << " vaddr=" << info.vaddr;
     }
   }
+
+  if (si_vec.empty() && IsKernelModule(binary_)) {
+    // For kernel modules without program headers, we simulate a loadable
+    // executable segment by using the file offset and link-time address of the
+    // .text section. We focus on .text and ignore other executable sections
+    // like .init.text and .exit.text as they are not important for steady-state
+    // performance.
+    ElfReader::SectionInfo info;
+    if (elf_reader.GetSectionInfoByName(".text", &info) != nullptr) {
+      add_loadable_exec_segment(info.offset, info.addr);
+    }
+  }
 }
 
 void SymbolMap::BuildSymbolMap() {

symbol_map_test.cc

@@ -16,6 +16,7 @@
 #include "base/logging.h"
 #include "llvm_profile_reader.h"
 #include "source_info.h"
+#include "util/symbolize/elf_reader.h"
 #include "gtest/gtest.h"
 #include "third_party/abseil/absl/container/node_hash_set.h"
 #include "third_party/abseil/absl/flags/flag.h"
@@ -524,4 +525,20 @@ TEST(AddressConversion, OffsetToVaddr) {
   EXPECT_EQ(symbol_map.GetFileOffsetFromStaticVaddr(0x001010), 0x002010);
 }
 
+TEST(AddressConversion, KernelModuleFakeSegment) {
+  SymbolMap symbol_map(absl::StrCat(testing::SrcDir(), kTestDataDir,
+                                    "test_kernel_module.ko"));
+  symbol_map.ReadLoadableExecSegmentInfo(/*is_kernel=*/false);
+
+  // Use ElfReader to get the actual .text section info from the test file.
+  devtools_crosstool_autofdo::ElfReader elf_reader(
+      absl::StrCat(testing::SrcDir(), kTestDataDir, "test_kernel_module.ko"));
+  devtools_crosstool_autofdo::ElfReader::SectionInfo info;
+  ASSERT_TRUE(elf_reader.GetSectionInfoByName(".text", &info) != nullptr);
+
+  // Verify that the fake segment maps the file offset to the address correctly.
+  EXPECT_EQ(symbol_map.GetFileOffsetFromStaticVaddr(info.addr), info.offset);
+  EXPECT_EQ(symbol_map.get_static_vaddr(info.offset), info.addr);
+}
+
 }  // namespace