1 files changed, 18 insertions, 10 deletions
diff --git a/src/common/linux/memory_mapped_file.cc b/src/common/linux/memory_mapped_file.cc
index 0f0fcb2b..064326bb 100644
--- a/src/common/linux/memory_mapped_file.cc
+++ b/src/common/linux/memory_mapped_file.cc
@@ -46,15 +46,15 @@ namespace google_breakpad {
 
 MemoryMappedFile::MemoryMappedFile() {}
 
-MemoryMappedFile::MemoryMappedFile(const char* path) {
-  Map(path);
+MemoryMappedFile::MemoryMappedFile(const char* path, size_t offset) {
+  Map(path, offset);
 }
 
 MemoryMappedFile::~MemoryMappedFile() {
   Unmap();
 }
 
-bool MemoryMappedFile::Map(const char* path) {
+bool MemoryMappedFile::Map(const char* path, size_t offset) {
   Unmap();
 
   int fd = sys_open(path, O_RDONLY, 0);
@@ -73,25 +73,33 @@ bool MemoryMappedFile::Map(const char* path) {
     return false;
   }
 
-  // If the file size is zero, simply use an empty MemoryRange and return
-  // true. Don't bother to call mmap() even though mmap() can handle an
-  // empty file on some platforms.
-  if (st.st_size == 0) {
+  // Strangely file size can be negative, but we check above that it is not.
+  size_t file_len = static_cast<size_t>(st.st_size);
+  // If the file does not extend beyond the offset, simply use an empty
+  // MemoryRange and return true. Don't bother to call mmap()
+  // even though mmap() can handle an empty file on some platforms.
+  if (offset >= file_len) {
     sys_close(fd);
     return true;
   }
 
 #if defined(__x86_64__) || defined(__aarch64__)
-  void* data = sys_mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+  void* data = sys_mmap(NULL, file_len, PROT_READ, MAP_PRIVATE, fd, offset);
 #else
-  void* data = sys_mmap2(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+  if ((offset & 4095) != 0) {
+    // Not page aligned.
+    sys_close(fd);
+    return false;
+  }
+  void* data = sys_mmap2(
+      NULL, file_len, PROT_READ, MAP_PRIVATE, fd, offset >> 12);
 #endif
   sys_close(fd);
   if (data == MAP_FAILED) {
     return false;
   }
 
-  content_.Set(data, st.st_size);
+  content_.Set(data, file_len - offset);
   return true;
 }