[PATCH] Loosen the Gold ODR checker to only compare filenames

[Jeffrey Yasskin]

This patch should do a better job. I went back to the
substring-comparison the original code used, and chopped off the line
number in addition to the directory. The code to remove the directory
is different because the original code wasn't a transitive relation:
it reported that "c:1" < "d/a:1" < "a/b:1" < "c:1".

2011-02-03  Jeffrey Yasskin  <jyasskin@google.com>

      * symtab.cc: Sort by just the filename.

On Thu, Feb 3, 2011 at 2:10 PM, Jeffrey Yasskin <jyasskin@google.com> wrote:
> Whoops, please don't submit this. The strings that Source_location
> points at don't live long enough to use them in the way I'm using
> them. I'll send a working patch shortly.
>
> On Wed, Feb 2, 2011 at 10:44 PM, Jeffrey Yasskin <jyasskin@google.com> wrote:
>> Code compiled with different flags, especially -O, may have a
>> different line number for the first instruction in a function. This
>> produces false positives in the ODR checker when linking object files
>> that should be ABI-compatible.
>>
>> The best fixes would be to A) look at the DW_AT_decl_line of the
>> DW_TAG_subprogram for the function, but this would require gold to
>> parse a whole new debug section, or B) hash the ODR-relevant aspects
>> of each function into a new dwarf attribute, but this would require
>> gcc to produce the hash and gold to parse a whole new debug section.
>>
>> Instead, loosening the ODR check to allow a function's definitions to
>> be from anywhere within the same file removes the false positives with
>> much less work, and would have caused very few extra false negatives
>> in Google's codebase.
>>
>> 2011-02-02  Jeffrey Yasskin  <jyasskin@google.com>
>>
>>       * dwarf_reader.h: Add a Source_location type, and change the
>> addr2line functions to return it.
>>       * dwarf_reader.cc: Implement Source_location, and change the
>> addr2line functions to return it.
>>       * symtab.cc: Sort by just the filename.
>>       * object.cc: Convert a Source_location return to a std::string.
>>
>
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