Re: discarding rules for duplicate ELF comdat groups

["Jan Beulich" <JBeulich at novell dot com>]

>>> 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.

Jan