Change MDCVInfoELF into something usable.

src/google_breakpad/common/minidump_format.h

Index: src/google_breakpad/common/minidump_format.h
diff --git a/src/google_breakpad/common/minidump_format.h b/src/google_breakpad/common/minidump_format.h
index 18f8268b2970b1d825b3e443b80b640bc5d62812..8e0790e4e1a86c1ff0ac38ab2f0a52164b397d3f 100644
--- a/src/google_breakpad/common/minidump_format.h
+++ b/src/google_breakpad/common/minidump_format.h
@@ -449,15 +449,22 @@ static const size_t MDCVInfoPDB70_minsize = offsetof(MDCVInfoPDB70,
 
 #define MD_CVINFOPDB70_SIGNATURE 0x53445352  /* cvSignature = 'SDSR' */
 
+/*
+ * Modern ELF toolchains insert a "build id" into the ELF headers that
+ * usually contains a hash of some ELF headers + sections to uniquely
+ * identify a binary.
+ * https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Developer_Guide/compiling-build-id.html
+ */
 typedef struct {
-  uint32_t data1[2];
-  uint32_t data2;
-  uint32_t data3;
-  uint32_t data4;
-  uint32_t data5[3];
-  uint8_t  extra[2];
+  uint32_t cv_signature;
+  uint8_t  build_id[1];  /* bytes of build id */

[Mark Mentovai, 2016/02/09 15:55:04]

How many?

[Ted Mielczarek, 2016/02/09 18:01:52]

There isn't really a spec for it, but it allows for an arbitrary number of
bytes. The binutils default is a 160-bit sha-1 hash of the rest of the binary,
so 20 bytes, but ld will let you use a uuid, md5, or an arbitrary hex string:
https://sourceware.org/binutils/docs-2.26/ld/Options.html#index-g_t_002d_002d...

Since the CV record is already variable-length, supporting arbitrary sizes here
isn't particularly hard. For the client-side patch I have to use this, I just
clamp it to a max of 20 bytes since that covers the common case and avoids
having to allocate memory in the minidump writer.

Should I just mention that it's variable-length, but usually 20 bytes?

 } MDCVInfoELF;
 
+static const size_t MDCVInfoELF_minsize = offsetof(MDCVInfoELF,
+                                                   build_id[0]);
+
+#define MD_CVINFOELF_SIGNATURE 0x4270454c  /* cvSignature = 'BpEL' */
+
 /* In addition to the two CodeView record formats above, used for linking
  * to external pdb files, it is possible for debugging data to be carried
  * directly in the CodeView record itself.  These signature values will