[PATCH 2/4] objdump: don't compare sections by name

[Jan Beulich]

On 27.02.2025 00:21, Alan Modra wrote:
> On Wed, Feb 26, 2025 at 12:58:55PM +0100, Jan Beulich wrote:
>> Multiple sections of the same name may exist (32-bit HPPA for example
>> looks to be keeping sections separate when combining object files with
>> ld -r). And really there's no reason to go by section name: We can
>> simply compare section pointers, as only a match with the section being
>> disassembled is of interest.
>> ---
>> Tests put in place by subsequent patches will cover this, on HPPA 32-bit
>> ELF.
>>
>> --- a/binutils/objdump.c
>> +++ b/binutils/objdump.c
>> @@ -1133,8 +1133,8 @@ compare_symbols (const void *ap, const v
>>       Don't sort symbols from other sections by section, since there
>>       isn't much reason to prefer one section over another otherwise.
>>       See sym_ok comment for why we compare by section name.  */
>> -  as = strcmp (compare_section->name, a->section->name) == 0;
>> -  bs = strcmp (compare_section->name, b->section->name) == 0;
>> +  as = compare_section == a->section;
>> +  bs = compare_section == b->section;
>>    if (as && !bs)
>>      return -1;
>>    if (!as && bs)
> 
> The sym_ok comment says:
>       /* Note - we cannot just compare section pointers because they could
> 	 be different, but the same...  Ie the symbol that we are trying to
> 	 find could have come from a separate debug info file.  Under such
> 	 circumstances the symbol will be associated with a section in the
> 	 debug info file, whilst the section we want is in a normal file.
> 	 So the section pointers will be different, but the section names
> 	 will be the same.  */

Hmm, but then what do we do? Comparing names clearly is wrong, as the
testcases added in the subsequent patch demonstrate.

Plus I'm in trouble with you saying "could have come from a separate debug
info file": What we disassemble are sections from "real" object files. In
particular compare_section isn't going to reference a debug info file. And
that's what we mean to special case here, as per the first sentence of the
comment (just out of context): "Prefer symbols from the section currently
being disassembled." (sym_ok() actually does both - first compare pointers
if the file is the same, and only then compare by name. I can't conclude
yet whether the latter is entirely correct. Nevertheless maybe you're
suggesting we similarly need to compare both here?)

What I need to do is drop the last sentence of this same comment.

Jan