Messages in this thread | | | Date | Wed, 30 Apr 2008 13:15:08 -0700 | From | Tom Rini <> | Subject | Re: [PATCH] /dev/mem gcc weak function workaround |
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On Wed, Apr 30, 2008 at 05:49:46AM -0700, Pallipadi, Venkatesh wrote: > > > >-----Original Message----- > >From: David Miller [mailto:davem@davemloft.net] > >Sent: Tuesday, April 29, 2008 9:29 PM > >To: Pallipadi, Venkatesh > >Cc: mingo@elte.hu; tglx@linutronix.de; hpa@zytor.com; > >akpm@linux-foundation.org; linux-kernel@vger.kernel.org > >Subject: Re: [PATCH] /dev/mem gcc weak function workaround > > > >From: Venki Pallipadi <venkatesh.pallipadi@intel.com> > >Date: Tue, 29 Apr 2008 18:31:09 -0700 > > > >> Some flavors of gcc 4.1.0 and 4.1.1 seems to have trouble > >understanding > >> 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 > >different > >> 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@intel.com> > >> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> > > > >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 > >file. > > > >We need something more bulletproof here. > > > > The references here > http://gcc.gnu.org/ml/gcc-bugs/2006-05/msg02801.html > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27781 > > seem to suggest that the bug is only with weak definition in the same > file. > So, having them in a different file should be good enough workaround > here. > > 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 question :)
-- Tom Rini
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