Re: discarding rules for duplicate ELF comdat groups

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

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.  */


-- 
H.J.