accept any build-id length between 4 and 20 bytes inclusive

[emaste]

Summary

There's a proposed patch D18091 adding build-id support to lld that would produce a 64-bit ID. There's some concern as existing tools typically expect the build-id to be either 16 or 20 bytes.

Prior to this change lldb would reject such a build-id, but that doesn't make sense given that lldb will fall back to a 4-byte crc32, a poorer quality identifier. Now we accept the build-id if it is 4 bytes or more.

[labath]

I think that's fine (you may want to add a note about the crc to the comment).

lldb/trunk/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

while (true)
                         }
                     }
                     break;
 
                 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))
+                        // 16 bytes is UUID|MD5, 20 bytes is SHA1. Other linkers may produce a build-id of a different
+                        // length. Accept it as long as it's at least 4 bytes as it will be better than our own crc32.
+                        if (note.n_descsz >= 4 && note.n_descsz <= 20)
                         {
                             uint8_t uuidbuf[20];
                             if (data.GetU8 (&offset, &uuidbuf, note.n_descsz) == nullptr)
                             {
                                 error.SetErrorString ("failed to read GNU_BUILD_ID note payload");
                                 return error;
                             }