Re: [PATCH] /dev/mem gcc weak function workaround
From: Tom Rini
Date: Wed Apr 30 2008 - 16:28:45 EST
On Wed, Apr 30, 2008 at 05:49:46AM -0700, Pallipadi, Venkatesh wrote:
> >-----Original Message-----
> >From: David Miller [mailto:davem@xxxxxxxxxxxxx]
> >Sent: Tuesday, April 29, 2008 9:29 PM
> >To: Pallipadi, Venkatesh
> >Cc: mingo@xxxxxxx; tglx@xxxxxxxxxxxxx; hpa@xxxxxxxxx;
> >akpm@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> >Subject: Re: [PATCH] /dev/mem gcc weak function workaround
> >From: Venki Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
> >Date: Tue, 29 Apr 2008 18:31:09 -0700
> >> Some flavors of gcc 4.1.0 and 4.1.1 seems to have trouble
> >> weak function definitions. Calls to function from the same
> >file where it is
> >> defined as weak _may_ get inlined, even when there is a
> >non-weak definition of
> >> the function elsewhere. I tried using attribute 'noinline'
> >which does not
> >> seem to help either.
> >> One workaround for this is to have weak functions defined in
> >> file as below. Other possible way is to not use weak
> >functions and go back
> >> to ifdef logic.
> >> There are few other usages in kernel that seem to depend on
> >weak (and noinline)
> >> working correctly, which can also potentially break and
> >needs such workarounds.
> >> Example -
> >> mach_reboot_fixups() in arch/x86/kernel/reboot.c is one such
> >call which
> >> is getting inlined with a flavor of gcc 4.1.1.
> >> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
> >> Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
> >This sounds like a bug. And if gcc does multi-file compilation it
> >can in theory do the same mistake even if you move it to another
> >We need something more bulletproof here.
> The references here
> seem to suggest that the bug is only with weak definition in the same
> So, having them in a different file should be good enough workaround
> Tom: Comments?
Yes, that matches my recollection. some versions of gcc 4.1.0 (and
possibly 4.1.1, it wouldn't be hard to check) could not handle having a
regular and weak function in the same file (I hit this trying to do
some abstraction or another in kgdb, using includes) but it was correct
if in separate files. I assume blacklisting 4.1.0 is out of the
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