Messages in this thread | | | From | Andrew Lutomirski <> | Date | Mon, 13 Jun 2011 13:06:26 -0400 | Subject | Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall_64.c |
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On Mon, Jun 13, 2011 at 1:05 PM, Rakib Mullick <rakib.mullick@gmail.com> wrote: > On Mon, Jun 13, 2011 at 8:18 PM, Andrew Lutomirski <luto@mit.edu> wrote: >> On Mon, Jun 13, 2011 at 10:14 AM, Ingo Molnar <mingo@elte.hu> wrote: >>> >>> * Andrew Lutomirski <luto@mit.edu> wrote: >>> >>>> On Mon, Jun 13, 2011 at 5:29 AM, Ingo Molnar <mingo@elte.hu> wrote: >>>> > >>>> > * Andrew Lutomirski <luto@mit.edu> wrote: >>>> > >>>> >> On Sat, Jun 11, 2011 at 3:31 AM, Rakib Mullick <rakib.mullick@gmail.com> wrote: >>>> >> > Due to commit 5cec93c216db77 (x86-64: Emulate legacy vsyscalls), we get the following warning: >>>> >> > >>>> >> > arch/x86/kernel/vsyscall_64.c: In function ‘do_emulate_vsyscall’: >>>> >> > arch/x86/kernel/vsyscall_64.c:111:7: warning: ‘ret’ may be used uninitialized in this function >>>> >> >>>> >> What's the code path that uses ret without initializing it? >>>> > >>>> > If the code is correct but GCC got confused then please use the >>>> > simplest possible patch to help GCC find its way around the code. >>>> >>>> The simplest patch is to mark ret as uninitialized_var. >>> >>> No - that primitive really sucks as it might hide *future* debug >>> warnings and silently break code. >>> >>> The problem with uninitialized_var() is that such code: >>> >>> int test(void) >>> { >>> int uninitialized_var(ret); >>> >>> return ret; >>> } >>> >>> Builds without a single warning but it is very broken code. >>> >>> So if we use uninitialized_var() and the code is changed in the >>> future to have the above broken sequence, we'll have a silent runtime >>> failure ... >>> >>> So we try to avoid using uninitialized_var() in arch/x86/ and use >>> explicit initialization instead. >>> >>> That way GCC that can see through the flow will optimize away the >>> superfluous initialization - GCC versions that are older will >>> generate one more instruction but that's OK. >> >> Fair enough. >> >> Unfortunately there doesn't seem to be an EKERNELBUG error code, and >> initializing to EFAULT seems silly. 0 is probably harmless. >> >> I'll wait awhile longer for that GCC version, since there might be a >> better fix. In any case, it would be nice for the changelog entry to >> say which version has a warning that's being worked around. >> > Well, I think I already posted the GCC version in this thread. Anyway, > for you're convenience, here is my GCC version: gcc version 4.5.1 > 20100924 (Red Hat 4.5.1-4). I'm using Fedora Core 14.
Sorry -- I think I managed to read every email in the thread except that one. Will test tonight.
--Andy
> > > Thanks, > Rakib > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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