Subject: Re: [Patch 1/4] Allow arch-specific cleanup before breakpoint unregistration

From: Michael Ellerman <[email-masked]>
Date: Thu, 27 May 2010 01:13:47 +1000

On Wed, 2010-05-26 at 10:54 +0100, David Howells wrote:
> K.Prasad <[email-masked]> wrote:
> 
> > > 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