simpleperf: use kernel start address in kernel mmap record.

The kernel start address is used to match with the start address in
.text section in vmlinux. It works even when kernel address space
layout randomization is used.

Bug: 172933381
Test: run simpleperf_unit_test
Change-Id: I3eb2bee8dd30b049504f4ec6f8f4b6d742cdd6b5

5 files changed, 38 insertions, 5 deletions

diff --git a/simpleperf/cmd_record_test.cpp b/simpleperf/cmd_record_test.cpp
index 917108af..cf228ae0 100644
--- a/simpleperf/cmd_record_test.cpp
+++ b/simpleperf/cmd_record_test.cpp
@@ -156,8 +156,7 @@ TEST(record_cmd, dump_kernel_mmap) {
   for (auto& record : records) {
     if (record->type() == PERF_RECORD_MMAP) {
       const MmapRecord* mmap_record = static_cast<const MmapRecord*>(record.get());
-      if (strcmp(mmap_record->filename, DEFAULT_KERNEL_MMAP_NAME) == 0 ||
-          strcmp(mmap_record->filename, DEFAULT_KERNEL_MMAP_NAME_PERF) == 0) {
+      if (android::base::StartsWith(mmap_record->filename, DEFAULT_KERNEL_MMAP_NAME)) {
         have_kernel_mmap = true;
         break;
       }
diff --git a/simpleperf/environment.cpp b/simpleperf/environment.cpp
index 9f3fd3bc..f3333ca1 100644
--- a/simpleperf/environment.cpp
+++ b/simpleperf/environment.cpp
@@ -175,10 +175,33 @@ static std::vector<KernelMmap> GetModulesInUse() {
   return module_mmaps;
 }
 
+static uint64_t GetKernelStartAddress() {
+  FILE* fp = fopen("/proc/kallsyms", "re");
+  if (fp == nullptr) {
+    return 0;
+  }
+  LineReader reader(fp);
+  char* line;
+  while ((line = reader.ReadLine()) != nullptr) {
+    if (strstr(line, "_stext") != nullptr) {
+      uint64_t addr;
+      if (sscanf(line, "%" PRIx64, &addr) == 1) {
+        return addr;
+      }
+    }
+  }
+  return 0;
+}
+
 void GetKernelAndModuleMmaps(KernelMmap* kernel_mmap, std::vector<KernelMmap>* module_mmaps) {
   kernel_mmap->name = DEFAULT_KERNEL_MMAP_NAME;
   kernel_mmap->start_addr = 0;
   kernel_mmap->len = std::numeric_limits<uint64_t>::max();
+  if (uint64_t kstart_addr = GetKernelStartAddress(); kstart_addr != 0) {
+    kernel_mmap->name = std::string(DEFAULT_KERNEL_MMAP_NAME) + "_stext";
+    kernel_mmap->start_addr = kstart_addr;
+    kernel_mmap->len = std::numeric_limits<uint64_t>::max() - kstart_addr;
+  }
   kernel_mmap->filepath = kernel_mmap->name;
   *module_mmaps = GetModulesInUse();
   for (auto& map : *module_mmaps) {
diff --git a/simpleperf/environment_test.cpp b/simpleperf/environment_test.cpp
index 8188ddb4..dd9d39f6 100644
--- a/simpleperf/environment_test.cpp
+++ b/simpleperf/environment_test.cpp
@@ -23,6 +23,8 @@
 #include "dso.h"
 #include "environment.h"
 #include "get_test_data.h"
+#include "test_util.h"
+#include "thread_tree.h"
 
 namespace fs = std::filesystem;
 
@@ -111,3 +113,13 @@ TEST(environment, GetModuleBuildId) {
   ASSERT_TRUE(GetModuleBuildId("fake_kernel_module", &build_id, GetTestData("sysfs")));
   ASSERT_EQ(build_id, BuildId("3e0ba155286f3454"));
 }
+
+TEST(environment, GetKernelAndModuleMmaps) {
+  TEST_REQUIRE_ROOT();
+  KernelMmap kernel_mmap;
+  std::vector<KernelMmap> module_mmaps;
+  GetKernelAndModuleMmaps(&kernel_mmap, &module_mmaps);
+  // The kernel map should contain the kernel start address.
+  ASSERT_EQ(kernel_mmap.name, std::string(DEFAULT_KERNEL_MMAP_NAME) + "_stext");
+  ASSERT_GT(kernel_mmap.start_addr, 0);
+}
diff --git a/simpleperf/thread_tree.cpp b/simpleperf/thread_tree.cpp
index 1818ff41..107e34d7 100644
--- a/simpleperf/thread_tree.cpp
+++ b/simpleperf/thread_tree.cpp
@@ -22,6 +22,7 @@
 
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
+#include <android-base/strings.h>
 
 #include "perf_event.h"
 #include "record.h"
@@ -133,7 +134,7 @@ void ThreadTree::AddKernelMap(uint64_t start_addr, uint64_t len, uint64_t pgoff,
 }
 
 Dso* ThreadTree::FindKernelDsoOrNew(const std::string& filename) {
-  if (filename == DEFAULT_KERNEL_MMAP_NAME || filename == DEFAULT_KERNEL_MMAP_NAME_PERF) {
+  if (android::base::StartsWith(filename, DEFAULT_KERNEL_MMAP_NAME)) {
     return kernel_dso_.get();
   }
   auto it = module_dso_tree_.find(filename);
diff --git a/simpleperf/thread_tree.h b/simpleperf/thread_tree.h
index 2c9a362e..aadfe71b 100644
--- a/simpleperf/thread_tree.h
+++ b/simpleperf/thread_tree.h
@@ -29,8 +29,6 @@
 struct Record;
 
 constexpr char DEFAULT_KERNEL_MMAP_NAME[] = "[kernel.kallsyms]";
-// Seen in perf.data file generated by perf.
-constexpr char DEFAULT_KERNEL_MMAP_NAME_PERF[] = "[kernel.kallsyms]_text";
 constexpr char DEFAULT_EXECNAME_FOR_THREAD_MMAP[] = "//anon";
 
 namespace simpleperf {