Launchpad has imported 4 comments from the remote bug at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553.
If you reply to an imported comment from within Launchpad, your comment will be sent to the remote bug automatically. Read more about Launchpad's inter-bugtracker facilities at https://documentation.ubuntu.com/launchpad/user/reference/bugs/multi-project-bugs/about-multi-project-bugs/#bugs-in-external-trackers. ------------------------------------------------------------------------ On 2009-12-30T12:56:51+00:00 Debian GCC maintainers wrote: current trunk/branches on x86_64-linux-gnu. return values with different compilers and different optimizations: -O0 -O1 -O2 -O3 gcc-4.1 0 2 2 2 gcc-4.3 0 2 2 2 gcc-4.4 2 0 0 0 gcc-4.5 0 1 0 0 Matthias #include <stdbool.h> #include <stdio.h> static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long bit) { bool res; __asm__ __volatile__( "btr %2,%1\n" "adc $0,%0\n" :"=r"(res), "=m"(*v) :"r"(bit), "r"(0)) ; return res ? 1 : 0; } int main(void) { unsigned long flags = 0; int j; j = atomic_test_and_reset_bit(&flags, 2); printf("%d\n", j); return 0; } Reply at: https://bugs.launchpad.net/ubuntu/+source/gcc-4.4/+bug/434527/comments/2 ------------------------------------------------------------------------ On 2009-12-30T13:14:52+00:00 Pinskia-gmail wrote: Subject: Re: New: wrong code with -O1 Sent from my iPhone On Dec 30, 2009, at 7:56 AM, "debian-gcc at lists dot debian dot org" <[email protected] > wrote: > current trunk/branches on x86_64-linux-gnu. return values with > different > compilers and different optimizations: > > -O0 -O1 -O2 -O3 > gcc-4.1 0 2 2 2 > gcc-4.3 0 2 2 2 > gcc-4.4 2 0 0 0 > gcc-4.5 0 1 0 0 > > Matthias > > #include <stdbool.h> > #include <stdio.h> > > static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long > bit) { > bool res; > > __asm__ __volatile__( "btr %2,%1\n" > "adc $0,%0\n" > :"=r"(res), "=m"(*v) > :"r"(bit), "r"(0)) ; > return res ? 1 : 0; This inline-asm looks wrong. Because it says *v is always overriden. So if that function is inlined, flags down below does not have to be set before it. > } > > int main(void) > { > unsigned long flags = 0; > int j; > > j = atomic_test_and_reset_bit(&flags, 2); > > printf("%d\n", j); > > return 0; > } > > > -- > Summary: wrong code with -O1 > Product: gcc > Version: 4.4.3 > Status: UNCONFIRMED > Severity: normal > Priority: P3 > Component: target > AssignedTo: unassigned at gcc dot gnu dot org > ReportedBy: debian-gcc at lists dot debian dot org > GCC target triplet: x86_64-linux-gnu > > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553 > Reply at: https://bugs.launchpad.net/ubuntu/+source/gcc-4.4/+bug/434527/comments/4 ------------------------------------------------------------------------ On 2009-12-30T14:33:01+00:00 Pinskia wrote: The inline-asm is totally incorrect here is the corrected version of the function (note res should be set): static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long bit) { bool res = 0; __asm__ __volatile__( "btr %2,%1\n" "adc $0,%0\n" :"+r"(res): "m"(*v) ,"r"(bit), "r"(0): "flags") ; return res ? 1 : 0; } Reply at: https://bugs.launchpad.net/ubuntu/+source/gcc-4.4/+bug/434527/comments/5 ------------------------------------------------------------------------ On 2010-01-04T16:07:49+00:00 Ubizjak wrote: (In reply to comment #2) > The inline-asm is totally incorrect here ... Actually, the asm is correct, it is just a couple of volatiles that are missing. Please see arch/x86/include/asm/bitops.h from linux-2.6 for correct implementation. Reply at: https://bugs.launchpad.net/ubuntu/+source/gcc-4.4/+bug/434527/comments/7 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/434527 Title: [PR42553] Compiled program misbehaves To manage notifications about this bug go to: https://bugs.launchpad.net/gcc/+bug/434527/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
