Messages in this thread | | | Date | Fri, 02 May 2008 14:09:53 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: huge gcc 4.1.{0,1} __weak problem |
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Adrian Bunk wrote: > On Wed, Apr 30, 2008 at 05:49:46AM -0700, Pallipadi, Venkatesh wrote: > >> >> >>> -----Original Message----- From: David Miller >>> 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. >> ... >> > > A workaround here is the wrong solution since this isn't the only place > that suffers from this issue. > > We currently give a #warning for 4.1.0. > But not for 4.1.1. > (Accordingto the bug >= 4.1.2 is fixed.) > > And a #warning is not enough. > > The huge problem is that "empty __weak function in the same file and > non-weak arch function" has recently become a common pattern with > several new usages added during this merge window alone. > > And the breakages can be very subtle runtime breakages. > > I see only the following choices: > - remove __weak and replace all current usages > - move all __weak functions into own files, and ensure that also happens > for future usages > - #error for gcc 4.1.{0,1} >
- make __weak also include noinline. I think that's sufficient (at least it was when I encountered a gcc bug with these symptoms last year or so).
J
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