On Wed, 2010-05-26 at 10:54 +0100, David Howells wrote:

K.Prasad [off-list ref] wrote:

quoted

quoted

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.

See the functions in kernel/softirq.c for example, and commits 43a256322
and b2e2fe996 - though unhelpfully they don't mention the gcc version. A
bit of googling suggests it was probably "gcc version 4.1.1 20060525
(Red Hat 4.1.1-1)" in that case.

But the example of hw_perf_enable() (which is weak in the same unit),
suggests maybe this isn't a bug many people are hitting in practice
anymore.

Having said that the #define foo foo pattern is reasonably neat and
avoids the problem altogether, see eg. arch_setup_msi_irqs.

cheers