Minidumper: Get the nexe's build ID from PT_NOTE when available

src/untrusted/minidump_generator/build_id.c

+/*
+ * Copyright (c) 2013 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+
+#include "native_client/src/include/elf32.h"
+
+
+extern const Elf32_Ehdr __ehdr_start __attribute__((weak));
+
+static uintptr_t note_align(uintptr_t value) {
+  return (value + 3) & ~3;
+}
+
+int nacl_get_build_id(const char **data, size_t *size) {
+  if (&__ehdr_start != NULL &&
+      __ehdr_start.e_ident[EI_CLASS] == ELFCLASS32 &&
+      __ehdr_start.e_phentsize == sizeof(Elf32_Phdr)) {
+    int phnum = __ehdr_start.e_phnum;
+    uintptr_t start_addr = (uintptr_t) &__ehdr_start;
+    Elf32_Phdr *phdrs = (Elf32_Phdr *) (start_addr + __ehdr_start.e_phoff);
+    for (int i = 0; i < phnum; ++i) {
+      Elf32_Phdr *phdr = &phdrs[i];
+      if (phdr->p_type == PT_NOTE) {
+        Elf32_Nhdr *note = (Elf32_Nhdr *) (start_addr + phdr->p_offset);
+        uintptr_t note_end = (uintptr_t) note + phdr->p_memsz;
+        while ((uintptr_t) note < note_end) {
+          uintptr_t name_ptr = (uintptr_t) &note[1];
+          assert(name_ptr <= note_end);
+          uintptr_t desc_ptr = note_align(name_ptr + note->n_namesz);
+          uintptr_t next_ptr = note_align(desc_ptr + note->n_descsz);
+          assert(next_ptr <= note_end);
+          if (note->n_type == NT_GNU_BUILD_ID) {

[Roland McGrath, 2013/05/10 16:58:13]

This needs to check that the name is "GNU" (four bytes including '\0').  The
n_type value that is NT_GNU_BUILD_ID for "GNU" has other meanings for other name
values.

[Mark Seaborn, 2013/05/10 18:25:28]

Ah, good point.  I hadn't quite realised it was namespaced like that.  Fixed.

Breakpad's file_id.cc also doesn't check this properly.

+            *data = (const char *) desc_ptr;
+            *size = note->n_descsz;
+            return 1;
+          }
+          note = (Elf32_Nhdr *) next_ptr;
+        }
+      }
+    }
+  }
+  return 0;
+}