Messages in this thread | | | Subject | Re: [PATCH] Fix Warnining in arch/x86/kernel/signal.c | From | Subrata Modak <> | Date | Wed, 13 May 2009 14:36:41 +0530 |
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On Wed, 2009-05-13 at 11:20 +0900, Hiroshi Shimamoto wrote: > Subrata Modak wrote: > > Hi, > > > >> On Tue, 2009-05-12 at 17:16 +0200, Andi Kleen wrote: > >> On Tue, May 12, 2009 at 05:16:14PM +0530, Subrata Modak wrote: > >> > >> Hi Subrata, > >> > >>> With gcc (GCC) 4.4.1 20090429 (prerelease), i get the following build warning: > >> Patch looks good (you can add a > >> Reviewed-by: Andi Kleen <ak@linux.intel.com>) > >> But I don't maintain this code anymore. Please resend to x86@kernel.org > >> cc linux-kernel@vger.kernel.org for merge. > >> > >> Thanks, > >> > >> -Andi > > > > > > With gcc (GCC) 4.4.1 20090429 (prerelease), i get the following build warning: > > > > CC arch/x86/kernel/signal.o > > arch/x86/kernel/signal.c: In function ‘sys_sigreturn’: > > arch/x86/kernel/signal.c:573: warning: ‘set.sig[1]’ may be used uninitialized in this function > > > > On investigation i found that this is because of the evaluation > > precedence of the expression below: > > > > 569 unsigned long sys_sigreturn(struct pt_regs *regs) > > 570 { > > 571 struct sigframe __user *frame; > > 572 unsigned long ax; > > 573 sigset_t set; > > 574 > > 575 frame = (struct sigframe __user *)(regs->sp - 8); > > 576 > > 577 if (!access_ok(VERIFY_READ, frame, sizeof(*frame))) > > 578 goto badframe; > > 579 if (__get_user(set.sig[0], &frame->sc.oldmask) || (_NSIG_WORDS > 1 > > 580 && __copy_from_user(&set.sig[1], &frame->extramask, > > 581 sizeof(frame->extramask)))) > > > > The initialization for set.sig[1] may not occur if > > __get_user(set.sig[0], &frame->sc.oldmask) > > evalutes to true. So, the compiler is complaining. > > > > I have devised a small patch for this which wanes away this warning > > without changing the conditional evaluation criteria. Let me know if > > you like this patch. > > > > 582 goto badframe; > > 583 > > 584 sigdelsetmask(&set, ~_BLOCKABLE); > > 585 spin_lock_irq(¤t->sighand->siglock); > > 586 current->blocked = set; > > 587 recalc_sigpending(); > > 588 spin_unlock_irq(¤t->sighand->siglock); > > 589 > > 590 if (restore_sigcontext(regs, &frame->sc, &ax)) > > 591 goto badframe; > > 592 return ax; > > 593 > > 594 badframe: > > 595 signal_fault(regs, frame, "sigreturn"); > > 596 > > 597 return 0; > > 598 } > > > > Signed-Off-By: Subrata Modak <subrata@linux.vnet.ibm.com> > > Reviewed-by: Andi Kleen <ak@linux.intel.com> > > To: <x86@kernel.org> > > Cc: Linux Kernel <linux-kernel@vger.kernel.org> > > Cc: Andi Kleen <andi@firstfloor.org> > > Cc: Andi Kleen <ak@linux.intel.com> > > Cc: Balbir Singh <balbir@linux.vnet.ibm.com> > > Cc: Sachin P Sant <sachinp@linux.vnet.ibm.com> > > Subject: [PATCH] Fix Warnining in arch/x86/kernel/signal.c > > --- > > > > --- a/arch/x86/kernel/signal.c 2009-05-12 10:59:24.000000000 +0530 > > +++ b/arch/x86/kernel/signal.c 2009-05-12 16:57:32.000000000 +0530 > > @@ -576,9 +576,10 @@ unsigned long sys_sigreturn(struct pt_re > > > > if (!access_ok(VERIFY_READ, frame, sizeof(*frame))) > > goto badframe; > > - if (__get_user(set.sig[0], &frame->sc.oldmask) || (_NSIG_WORDS > 1 > > - && __copy_from_user(&set.sig[1], &frame->extramask, > > - sizeof(frame->extramask)))) > > + > > + if ( (__copy_from_user(&set.sig[1], &frame->extramask, > > + sizeof(frame->extramask)) && _NSIG_WORDS > 1) || > > + __get_user(set.sig[0], &frame->sc.oldmask)) > > goto badframe; > > I'm not sure why this eliminates that warning. > set.sig[0] may not be initialized too, if __copy_from_user() failed.
True, but only when either or both of __copy_from_user() and (_NSIG_WORDS > 1) fails. But in all instances set.sig[1] gets initialized.
> I don't have enough time to look at this right now, sorry. > > Another question, __copy_from_user() will be called even if > _NSIG_WORDS is less than 2, perhaps it never occurs. > I think, to check _NSIG_WORDS > 1 before calling __copy_from_user() > is better.
Fine. Let Ingo/Thomas/Peter decide whether they would like this fix or drop it.
Regards-- Subrata
> > Thanks, > Hiroshi >
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