[PATCH] D18055: ELF: Implement --build-id.

[Ed Maste via llvm-commits]

On 11 March 2016 at 14:52, Rui Ueyama <ruiu at google.com> wrote:
> It doesn't seem to make sense to leave 8 byte blank in the .note section.
> I'd think that setting the size to 8 byte conveys the message that there is
> a chance of collision, too. So I guess that keeping it 8 bytes is a good
> idea.

It turns out that lldb only accepts 16 and 20 byte build-ids today:

                case LLDB_NT_GNU_BUILD_ID_TAG:
                    // Only bother processing this if we don't already
have the uuid set.
                    if (!uuid.IsValid())
                    {
                        // 16 bytes is UUID|MD5, 20 bytes is SHA1
                        if ((note.n_descsz == 16 || note.n_descsz == 20))
                        { ...

however, it uses a zero-padded crc32 in the absence of build-id so
it's already willing to deal with shorter identifiers:

[  0] 7D9D49C0-0000-0000-0000-000000000000                    /bin/ls
      /usr/lib/debug/bin/ls.debug

Refusing an 8-byte build-id and using a 4-byte crc instead doesn't
seem sensible, so I'll post an lldb patch to accept anything >= 4
bytes.