Messages in this thread | | | Date | Thu, 1 May 2008 15:20:51 -0700 | From | Andrew Morton <> | Subject | Re: huge gcc 4.1.{0,1} __weak problem |
| |
On Fri, 2 May 2008 00:56:33 +0300 Adrian Bunk <bunk@kernel.org> 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
Perhaps the commonest. Certainly there will be more.
> 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}
Can we detect the {0,1}? __GNUC_EVEN_MORE_MINOR__?
Yes, I guess we should ban 4.1.x. Ouch.
| |