On Wed, 2010-05-26 at 10:54 +0100, David Howells wrote: > K.Prasad <pra...@linux.vnet.ibm.com> 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
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