Re: discarding rules for duplicate ELF comdat groups

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Jan 28, 2011 at 7:28 AM, Jan Beulich <JBeulich@novell.com> wrote:
>>>> On 28.01.11 at 15:40, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>> On Fri, Jan 28, 2011 at 6:30 AM, Jan Beulich <JBeulich@novell.com> wrote:
>>>>>> On 28.01.11 at 15:07, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>>> On Fri, Jan 28, 2011 at 5:51 AM, Jan Beulich <JBeulich@novell.com> wrote:
>>>>> It seems like currently the rule simply is to pick the first instance the
>>>>> linker gets to see. Wouldn't it make sense to honor the group
>>>>> signature's attributed (namely its binding), and prefer keeping an
>>>>> instance with a global group signature over a weak or local one?
>>>>> That would allow the programmer some control over which
>>>>> instance to keep: My main motivation is to find a way to discard
>>>>> the various weak fallback functions Linux has to cover cases where
>>>>> e.g. some architectures implement certain functionality, while
>>>>> others that don't can all use a generic implementation.
>>>>>
>>>>> I cannot see other mechanisms that would allow ld to discard
>>>>> sections (not to speak of individual functions within sections).
>>>>>
>>>>
>>>> Microsoft linker has some user controls over which comdat group
>>>> instance to keep. ?Will its scheme work for you?
>>>
>>> I'm not aware of any such controls - can you point me to
>>> something describing this?
>>
>> /* COMDAT selection codes. ?*/
>>
>> #define IMAGE_COMDAT_SELECT_NODUPLICATES ? ? (1) /* Warn if duplicates. ?*/
>> #define IMAGE_COMDAT_SELECT_ANY ? ? ? ? ? ? ?(2) /* No warning. ?*/
>> #define IMAGE_COMDAT_SELECT_SAME_SIZE ? ? ? ?(3) /* Warn if different size.
>> */
>> #define IMAGE_COMDAT_SELECT_EXACT_MATCH ? ? ?(4) /* Warn if different. ?*/
>> #define IMAGE_COMDAT_SELECT_ASSOCIATIVE ? ? ?(5) /* Base on other section.
>> */
>
> Oh, those you meant. No, they don't allow controlling which
> instance will be retained.
>

You can always propose something.


-- 
H.J.