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Re: [PATCH] Remove divide from _ELF_DYNAMIC_DO_RELOC
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Chung-Lin Tang <chunglin_tang at mentor dot com>, libc-alpha at sourceware dot org
- Cc: David Miller <davem at davemloft dot net>, "Joseph S. Myers" <joseph at codesourcery dot com>, OndÅej BÃlka <neleai at seznam dot cz>
- Date: Tue, 15 Jul 2014 16:30:11 -0400
- Subject: Re: [PATCH] Remove divide from _ELF_DYNAMIC_DO_RELOC
- Authentication-results: sourceware.org; auth=none
- References: <5347B7EE dot 6020507 at mentor dot com> <537F542B dot 5040409 at redhat dot com> <53C4C1D5 dot 40002 at mentor dot com>
On 07/15/2014 01:53 AM, Chung-Lin Tang wrote:
> Hi Carlos, thanks for the review, and sorry about the long delay to reply.
>
> On 14/5/23 9:59 PM, Carlos O'Donell wrote:
>> On 04/11/2014 05:37 AM, Chung-Lin Tang wrote:
>>> 2014-04-11 Chung-Lin Tang <cltang@codesourcery.com>
>>>
>>> * elf/dynamic-link.h (_ELF_DYNAMIC_DO_RELOC): Remove MIN() and
>>> assign raw DT_REL[A]COUNT value to ranges[0].nrelative.
OK to checkin.
>>> diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
>>> index 7b3e295..34ef88a 100644
>>> --- a/elf/dynamic-link.h
>>> +++ b/elf/dynamic-link.h
>>> @@ -122,8 +122,7 @@ elf_machine_lazy_rel (struct link_map *map,
>>> ranges[0].size = (map)->l_info[DT_##RELOC##SZ]->d_un.d_val; \
>>> if (map->l_info[VERSYMIDX (DT_##RELOC##COUNT)] != NULL) \
>>> ranges[0].nrelative \
>>> - = MIN (map->l_info[VERSYMIDX (DT_##RELOC##COUNT)]->d_un.d_val, \
>>> - ranges[0].size / sizeof (ElfW(reloc))); \
>>> + = map->l_info[VERSYMIDX (DT_##RELOC##COUNT)]->d_un.d_val; \
I want to note that the resulting code is less robust against binutils
bugs where the COUNT is more than the number of relocations in the list.
However I would rather this fail here quickly than magically select
DT_RELSZ/sizeof(ElfW(reloc)) as some random fallback e.g. all the relocs
are relative.
>>> } \
>>> if ((map)->l_info[DT_PLTREL] \
>>> && (!test_rel || (map)->l_info[DT_PLTREL]->d_un.d_val == DT_##RELOC)) \
>>
>> Please add a top-level comment saying that 'COUNT', when present, overrides the
>> use of 'SZ' to compute the size of the range.
>
> When 'COUNT' is not present, nrelative seems to be simply initialized as
> zero. I don't think it has to do with range here.
You are correct, I incorrectly remembered the purpose of DT_RELCOUNT which is
to handle the combined R_*_RELATIVE relocations more optimally in one block.
>> OK with that.
>>
>> Should we assert if SZ/sizeof(ElfW(reloc)) != COUNT?
>
> Please, please don't introduce another divide, defeating my original
> purpose...
Given that I incorrectly remembered by DT_RELCOUNT was for this recommendation
is not correct anyway.
Therefore your patch as-is can be checked in. Please ask Allan McRae for permission
since this is a freeze period and we are fixing bugs, documentation and other things.
Cheers,
Carlos.