On Wed, May 26, 2010 at 10:47:42PM +0530, K.Prasad wrote:

On Wed, May 26, 2010 at 10:54:41AM +0100, David Howells wrote:

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K.Prasad [off-list ref] wrote:

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My understanding is weak function definitions must appear in a different C
file than their call sites to work on some toolchains.

Atleast, there are quite a few precedents inside the Linux kernel for
__weak functions being invoked from the file in which they are defined
(arch_hwblk_init, arch_enable_nonboot_cpus_begin and hw_perf_disable to
name a few).
Moreover the online GCC docs haven't any such constraints mentioned.

I've seen problems in this area.  gcc sometimes inlines a weak function that's
in the same file as the call point.

We've seen such behaviour even otherwise....even with noinline attribute
in place. I'm not sure if this gcc fix
(http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16922) helped correct the
behaviour, but the lesson has been to not trust a function to be
inlined/remain non-inline consistently.

If we can't put the call to the function in the same file of its weak
definition, then perf is totally screwed.

And in fact it makes __weak basically useless and unusable. I guess
that happened in old gcc versions that have been fixed now.

Anyway, I'm personally fine with this patch (you can put my hack
if you want).

Thanks.