[Fuchsia] Output new-style Fuchsia stack traces.

Migrate base::debug::StackTrace to emit stack traces in the new
format documented at
https://fuchsia.googlesource.com/zircon/+/master/docs/symbolizer_markup.md

Bug: 777252
Change-Id: If42d62af4d358efc3ba61af2b6118026eec9a15f
Reviewed-on: https://chromium-review.googlesource.com/c/1474678
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636114}

base/debug/stack_trace_fuchsia.cc

@@ -4,9 +4,9 @@
 
 #include "base/debug/stack_trace.h"
 
+#include <elf.h>
 #include <link.h>
 #include <stddef.h>
-#include <string.h>
 #include <threads.h>
 #include <unwind.h>
 #include <zircon/process.h>
@@ -21,7 +21,10 @@
 #include <iostream>
 #include <type_traits>
 
+#include "base/atomic_sequence_num.h"
+#include "base/debug/elf_reader.h"
 #include "base/logging.h"
+#include "base/no_destructor.h"
 #include "base/stl_util.h"
 
 namespace base {
@@ -30,7 +33,7 @@ namespace debug {
 namespace {
 
 const char kProcessNamePrefix[] = "app:";
-const size_t kProcessNamePrefixLen = base::size(kProcessNamePrefix) - 1;
+const size_t kProcessNamePrefixLength = base::size(kProcessNamePrefix) - 1;
 
 struct BacktraceData {
   void** trace_array;
@@ -49,20 +52,53 @@ _Unwind_Reason_Code UnwindStore(struct _Unwind_Context* context,
   return _URC_NO_REASON;
 }
 
+// Build a "rwx" C string-based representation of the permission bits.
+// The output buffer is reused across calls, and should not be retained across
+// consecutive invocations of this function.
+const char* PermissionFlagsToString(int flags, char permission_buf[4]) {
+  char* permission = permission_buf;
+
+  if (flags & PF_R)
+    (*permission++) = 'r';
+
+  if (flags & PF_W)
+    (*permission++) = 'w';
+
+  if (flags & PF_X)
+    (*permission++) = 'x';
+
+  *permission = '\0';
+
+  return permission_buf;
+}
+
 // Stores and queries debugging symbol map info for the current process.
 class SymbolMap {
  public:
-  struct Entry {
-    void* addr;
-    char name[ZX_MAX_NAME_LEN + kProcessNamePrefixLen];
+  struct Segment {
+    const void* addr = nullptr;
+    size_t relative_addr = 0;
+    int permission_flags = 0;
+    size_t size = 0;
+  };
+
+  struct Module {
+    // Maximum number of PT_LOAD segments to process per ELF binary. Most
+    // binaries have only 2-3 such segments.
+    static constexpr size_t kMaxSegmentCount = 8;
+
+    const void* addr = nullptr;
+    std::array<Segment, kMaxSegmentCount> segments;
+    size_t segment_count = 0;
+    char name[ZX_MAX_NAME_LEN + kProcessNamePrefixLength + 1] = {0};
+    char build_id[kMaxBuildIdStringLength + 1] = {0};
   };
 
   SymbolMap();
   ~SymbolMap() = default;
 
-  // Gets the symbol map entry for |address|. Returns null if no entry could be
-  // found for the address, or if the symbol map could not be queried.
-  Entry* GetForAddress(void* address);
+  // Gets all entries for the symbol map.
+  span<Module> GetModules() { return {modules_.data(), count_}; }
 
  private:
   // Component builds of Chrome pull about 250 shared libraries (on Linux), so
@@ -72,7 +108,7 @@ class SymbolMap {
   void Populate();
 
   // Sorted in descending order by address, for lookup purposes.
-  std::array<Entry, kMaxMapEntries> entries_;
+  std::array<Module, kMaxMapEntries> modules_;
 
   size_t count_ = 0;
   bool valid_ = false;
@@ -84,21 +120,6 @@ SymbolMap::SymbolMap() {
   Populate();
 }
 
-SymbolMap::Entry* SymbolMap::GetForAddress(void* address) {
-  if (!valid_) {
-    return nullptr;
-  }
-
-  // Working backwards in the address space, return the first map entry whose
-  // address comes before |address| (thereby enclosing it.)
-  for (size_t i = 0; i < count_; ++i) {
-    if (address >= entries_[i].addr) {
-      return &entries_[i];
-    }
-  }
-  return nullptr;
-}
-
 void SymbolMap::Populate() {
   zx_handle_t process = zx_process_self();
 
@@ -107,11 +128,11 @@ void SymbolMap::Populate() {
   // TODO(wez): Object names can only have up to ZX_MAX_NAME_LEN characters, so
   // if we keep hitting problems with truncation, find a way to plumb argv[0]
   // through to here instead, e.g. using CommandLine::GetProgramName().
-  char app_name[std::extent<decltype(SymbolMap::Entry::name)>()];
-  strcpy(app_name, kProcessNamePrefix);
+  char app_name[std::extent<decltype(SymbolMap::Module::name)>()];
+  strncpy(app_name, kProcessNamePrefix, sizeof(kProcessNamePrefix));
   zx_status_t status = zx_object_get_property(
-      process, ZX_PROP_NAME, app_name + kProcessNamePrefixLen,
-      sizeof(app_name) - kProcessNamePrefixLen);
+      process, ZX_PROP_NAME, app_name + kProcessNamePrefixLength,
+      sizeof(app_name) - kProcessNamePrefixLength);
   if (status != ZX_OK) {
     DPLOG(WARNING)
         << "Couldn't get name, falling back to 'app' for program name: "
@@ -136,23 +157,67 @@ void SymbolMap::Populate() {
     return;
   }
 
-  // Copy the contents of the link map linked list to |entries_|.
+  // Populate ELF binary metadata into |modules_|.
   while (lmap != nullptr) {
-    if (count_ >= entries_.size()) {
+    if (count_ >= kMaxMapEntries)
+      break;
+
+    SymbolMap::Module& next_entry = modules_[count_];
+    ++count_;
+
+    next_entry.addr = reinterpret_cast<void*>(lmap->l_addr);
+
+    // Create Segment sub-entries for all PT_LOAD headers.
+    // Each Segment corresponds to a "mmap" line in the output.
+    next_entry.segment_count = 0;
+    for (const Elf64_Phdr& phdr : GetElfProgramHeaders(next_entry.addr)) {
+      if (phdr.p_type != PT_LOAD)
+        continue;
+
+      if (next_entry.segment_count > Module::kMaxSegmentCount) {
+        LOG(WARNING) << "Exceeded the maximum number of segments.";
         break;
       }
-    SymbolMap::Entry* next_entry = &entries_[count_];
-    count_++;
 
-    next_entry->addr = reinterpret_cast<void*>(lmap->l_addr);
-    char* name_to_use = lmap->l_name[0] ? lmap->l_name : app_name;
-    strlcpy(next_entry->name, name_to_use, sizeof(next_entry->name));
-    lmap = lmap->l_next;
+      Segment segment;
+      segment.addr =
+          reinterpret_cast<const char*>(next_entry.addr) + phdr.p_vaddr;
+      segment.relative_addr = phdr.p_vaddr;
+      segment.size = phdr.p_memsz;
+      segment.permission_flags = phdr.p_flags;
+
+      next_entry.segments[next_entry.segment_count] = std::move(segment);
+      ++next_entry.segment_count;
+    }
+
+    // Get the human-readable library name from the ELF header, falling back on
+    // using names from the link map for binaries that aren't shared libraries.
+    Optional<StringPiece> elf_library_name =
+        ReadElfLibraryName(next_entry.addr);
+    if (elf_library_name) {
+      strlcpy(next_entry.name, elf_library_name->data(),
+              elf_library_name->size() + 1);
+    } else {
+      StringPiece link_map_name(lmap->l_name[0] ? lmap->l_name : app_name);
+
+      // The "module" stack trace annotation doesn't allow for strings which
+      // resemble paths, so extract the filename portion from |link_map_name|.
+      size_t directory_prefix_idx = link_map_name.find_last_of("/");
+      if (directory_prefix_idx != StringPiece::npos) {
+        link_map_name = link_map_name.substr(
+            directory_prefix_idx + 1,
+            link_map_name.size() - directory_prefix_idx - 1);
+      }
+      strlcpy(next_entry.name, link_map_name.data(), link_map_name.size() + 1);
+    }
+
+    if (!ReadElfBuildId(next_entry.addr, false, next_entry.build_id)) {
+      LOG(WARNING) << "Couldn't read build ID.";
+      continue;
     }
 
-  std::sort(
-      entries_.begin(), entries_.begin() + count_,
-      [](const Entry& a, const Entry& b) -> bool { return a.addr > b.addr; });
+    lmap = lmap->l_next;
+  }
 
   valid_ = true;
 }
@@ -180,39 +245,35 @@ void StackTrace::PrintWithPrefix(const char* prefix_string) const {
   OutputToStreamWithPrefix(&std::cerr, prefix_string);
 }
 
-// Sample stack trace output is designed to be similar to Fuchsia's crashlogger:
-// bt#00: pc 0x1527a058aa00 (app:/system/base_unittests,0x18bda00)
-// bt#01: pc 0x1527a0254b5c (app:/system/base_unittests,0x1587b5c)
-// bt#02: pc 0x15279f446ece (app:/system/base_unittests,0x779ece)
-// ...
-// bt#21: pc 0x1527a05b51b4 (app:/system/base_unittests,0x18e81b4)
-// bt#22: pc 0x54fdbf3593de (libc.so,0x1c3de)
-// bt#23: end
+// Emits stack trace data using the symbolizer markup format specified at:
+// https://fuchsia.googlesource.com/zircon/+/master/docs/symbolizer_markup.md
 void StackTrace::OutputToStreamWithPrefix(std::ostream* os,
                                           const char* prefix_string) const {
   SymbolMap map;
 
-  size_t i = 0;
-  for (; (i < count_) && os->good(); ++i) {
-    SymbolMap::Entry* entry = map.GetForAddress(trace_[i]);
-    if (prefix_string)
-      *os << prefix_string;
-    if (entry) {
-      size_t offset = reinterpret_cast<uintptr_t>(trace_[i]) -
-                      reinterpret_cast<uintptr_t>(entry->addr);
-      *os << "bt#" << std::setw(2) << std::setfill('0') << i << std::setw(0)
-          << ": pc " << trace_[i] << " (" << entry->name << ",0x" << std::hex
-          << offset << std::dec << std::setw(0) << ")\n";
-    } else {
-      // Fallback if the DSO map isn't available.
-      // Logged PC values are absolute memory addresses, and the shared object
-      // name is not emitted.
-      *os << "bt#" << std::setw(2) << std::setfill('0') << i << std::setw(0)
-          << ": pc " << trace_[i] << "\n";
+  int module_id = 0;
+  *os << "{{{reset}}}\n";
+  for (const SymbolMap::Module& entry : map.GetModules()) {
+    *os << "{{{module:" << module_id << ":" << entry.name
+        << ":elf:" << entry.build_id << "}}}\n";
+
+    for (size_t i = 0; i < entry.segment_count; ++i) {
+      const SymbolMap::Segment& segment = entry.segments[i];
+
+      char permission_string[4] = {};
+      *os << "{{{mmap:" << segment.addr << ":0x" << std::hex << segment.size
+          << std::dec << ":load:" << module_id << ":"
+          << PermissionFlagsToString(segment.permission_flags,
+                                     permission_string)
+          << ":"
+          << "0x" << std::hex << segment.relative_addr << std::dec << "}}}\n";
     }
+
+    ++module_id;
   }
 
-  (*os) << "bt#" << std::setw(2) << i << ": end\n";
+  for (size_t i = 0; i < count_; ++i)
+    *os << "{{{bt:" << i << ":" << trace_[i] << "}}}\n";
 }
 
 }  // namespace debug