Launchpad has imported 2 comments from the remote bug at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60581.
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://help.launchpad.net/InterBugTracking. ------------------------------------------------------------------------ On 2014-03-19T09:07:48+00:00 Rafał Mużyło wrote: The problem is described here: https://bugs.gentoo.org/show_bug.cgi?id=505026 The code to trigger comes from a launchpad bug: https://bugs.launchpad.net/ubuntu/+source/gcc-defaults/+bug/1072650 As you may notice, it's acros distros and affects many compiler versions (confirmed for 4.6.3 on ubuntu, 4.7.3 and 4.8.2 on Gentoo). Following code (AFAICT) violates strict aliasing rules: #include <stdio.h> struct psuedo_hdr { int saddr; int daddr; char zero; char protocol; short len; } __attribute__((packed)); int main() { unsigned int i; unsigned int sum = 0; struct psuedo_hdr hdr; hdr.saddr = 0xaabbccdd; hdr.daddr = 0x11223344; hdr.zero = 0; hdr.protocol = 6; hdr.len = 2; for (i = 0; i < sizeof(hdr); i += 2) sum += *(short *)((char *)(&hdr) + i); printf("0x%x\n", sum); return 0; } however, '-O2 -Wall' doesn't result in the strict aliasing warning. Reply at: https://bugs.launchpad.net/ubuntu/+source/gcc- defaults/+bug/1072650/comments/3 ------------------------------------------------------------------------ On 2014-03-19T10:00:27+00:00 Rguenth wrote: The strict-aliasing warnings are broken - they are too easily to silence (the (char *) cast for example). Generally warning for TBAA violations is very hard if you want to avoid gazillions of false positives or gazillions of false negatives. The present warning code delivers neither :/ Reply at: https://bugs.launchpad.net/ubuntu/+source/gcc- defaults/+bug/1072650/comments/5 ** Changed in: gcc-defaults Status: Unknown => Confirmed ** Changed in: gcc-defaults Importance: Unknown => Medium -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1072650 Title: gcc doesn't isssue a strict aliasing warning on a code that seems to break it To manage notifications about this bug go to: https://bugs.launchpad.net/gcc-defaults/+bug/1072650/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
