Issue 357: New Linux file_id code doesn't persist across strip. r=agl,nealsid at http://breakpad.appspot.com/49008

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@461 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/linux/file_id.cc

@@ -33,6 +33,8 @@
 //
 
 #include "common/linux/file_id.h"
+#include "common/linux/linux_libc_support.h"
+#include "common/linux/linux_syscall_support.h"
 
 #include <arpa/inet.h>
 #include <elf.h>
@@ -42,6 +44,7 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+#include <algorithm>
 #include <cassert>
 #include <cstdio>
 
@@ -51,33 +54,94 @@ FileID::FileID(const char* path) {
   strncpy(path_, path, sizeof(path_));
 }
 
+// These two functions are also used inside the crashed process, so be safe
+// and use the syscall/libc wrappers instead of direct syscalls or libc.
+  static bool FindElfTextSection(const void *elf_mapped_base,
+                                 const void **text_start,
+                                 int *text_size) {
+  assert(elf_mapped_base);
+  assert(text_start);
+  assert(text_size);
+
+  const char* elf_base =
+    static_cast<const char*>(elf_mapped_base);
+  const ElfW(Ehdr)* elf_header =
+    reinterpret_cast<const ElfW(Ehdr)*>(elf_base);
+  if (my_strncmp(elf_base, ELFMAG, SELFMAG) != 0)
+    return false;
+#if __ELF_NATIVE_CLASS == 32
+#define ELFCLASS ELFCLASS32
+#else
+#define ELFCLASS ELFCLASS64
+#endif
+  //TODO: support dumping 32-bit binaries from a 64-bit dump_syms?
+  if (elf_header->e_ident[EI_CLASS] != ELFCLASS)
+    return false;
+  *text_start = NULL;
+  *text_size = 0;
+  const ElfW(Shdr)* sections =
+    reinterpret_cast<const ElfW(Shdr)*>(elf_base + elf_header->e_shoff);
+  const char* text_section_name = ".text";
+  int name_len = my_strlen(text_section_name);
+  const ElfW(Shdr)* string_section = sections + elf_header->e_shstrndx;
+  const ElfW(Shdr)* text_section = NULL;
+  for (int i = 0; i < elf_header->e_shnum; ++i) {
+    if (sections[i].sh_type == SHT_PROGBITS) {
+      const char* section_name = (char*)(elf_base +
+                                         string_section->sh_offset +
+                                         sections[i].sh_name);
+      if (!my_strncmp(section_name, text_section_name, name_len)) {
+        text_section = &sections[i];
+        break;
+      }
+    }
+  }
+  if (text_section != NULL && text_section->sh_size > 0) {
+    *text_start = elf_base + text_section->sh_offset;
+    *text_size = text_section->sh_size;
+  }
+  return true;
+}
+
+// static
+bool FileID::ElfFileIdentifierFromMappedFile(void* base,
+                                             uint8_t identifier[kMDGUIDSize])
+{
+  const void* text_section = NULL;
+  int text_size = 0;
+  bool success = false;
+  if (FindElfTextSection(base, &text_section, &text_size) && (text_size > 0)) {
+    my_memset(identifier, 0, kMDGUIDSize);
+    const uint8_t* ptr = reinterpret_cast<const uint8_t*>(text_section);
+    const uint8_t* ptr_end = ptr + std::min(text_size, 4096);
+    while (ptr < ptr_end) {
+      for (unsigned i = 0; i < kMDGUIDSize; i++)
+        identifier[i] ^= ptr[i];
+      ptr += kMDGUIDSize;
+    }
+    success = true;
+  }
+  return success;
+}
+
 bool FileID::ElfFileIdentifier(uint8_t identifier[kMDGUIDSize]) {
-  const ssize_t mapped_len = 4096;  // Page size (matches WriteMappings())
   int fd = open(path_, O_RDONLY);
   if (fd < 0)
     return false;
   struct stat st;
-  if (fstat(fd, &st) != 0 || st.st_size <= mapped_len) {
+  if (fstat(fd, &st) != 0) {
     close(fd);
     return false;
   }
-  void* base = mmap(NULL, mapped_len,
+  void* base = mmap(NULL, st.st_size,
                     PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
   close(fd);
   if (base == MAP_FAILED)
     return false;
 
-  memset(identifier, 0, kMDGUIDSize);
-  uint8_t* ptr = reinterpret_cast<uint8_t*>(base);
-  uint8_t* ptr_end = ptr + mapped_len;
-  while (ptr < ptr_end) {
-    for (unsigned i = 0; i < kMDGUIDSize; i++)
-      identifier[i] ^= ptr[i];
-    ptr += kMDGUIDSize;
-  }
-
-  munmap(base, mapped_len);
-  return true;
+  bool success = ElfFileIdentifierFromMappedFile(base, identifier);
+  munmap(base, st.st_size);
+  return success;
 }
 
 // static