[Bug lto/62249] Spurious FORTIFY_SOURCE warning with -flto, poll

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62249

Richard Biener  changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |DUPLICATE

--- Comment #6 from Richard Biener  ---
Duplicate.

*** This bug has been marked as a duplicate of bug 61886 ***

[Bug lto/62249] Spurious FORTIFY_SOURCE warning with -flto, poll

[crrodriguez at opensuse dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62249

Cristian Rodríguez  changed:

   What|Removed |Added

 CC||crrodriguez at opensuse dot org

--- Comment #5 from Cristian Rodríguez  ---
This bug also affects building systemd with LTO enabled.

[Bug lto/62249] Spurious FORTIFY_SOURCE warning with -flto, poll

[zackw at panix dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62249

--- Comment #4 from Zack Weinberg  ---
The "delta-minimized self-contained test case" should require only `-O2 -flto`
to reproduce the problem.  The other test case, however, should require
`-D_FORTIFY_SOURCE=2` in addition, and to be compiled against recent glibc.

Note also that this does not happen with 4.8 or older.

[Bug lto/62249] Spurious FORTIFY_SOURCE warning with -flto, poll

[i.palachev at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62249

Ilya Palachev  changed:

   What|Removed |Added

 CC||i.palachev at samsung dot com

--- Comment #3 from Ilya Palachev  ---
The bug reproduces for me even without -D_FORTIFY_SOURCE=2.

[Bug lto/62249] Spurious FORTIFY_SOURCE warning with -flto, poll

[zackw at panix dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62249

--- Comment #2 from Zack Weinberg  ---
Incidentally, yes, the test case is based on a real program.

[Bug lto/62249] Spurious FORTIFY_SOURCE warning with -flto, poll

[zackw at panix dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62249

--- Comment #1 from Zack Weinberg  ---
Created attachment 33389
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33389&action=edit
Delta-minimized self-contained test case

Requires no headers anymore.

Delta-minimization revealed something interesting:

int __poll_chk (struct pollfd *, unsigned, int, unsigned);
int __poll_chk_warn (struct pollfd *, unsigned, int, unsigned)
  __asm__ ("__poll_chk")
  __attribute__ ((__warning__ ("poll called with fds buffer too small")));

The __asm__("__poll_chk") annotation is essential; if it's removed the bug goes
away.  I don't know anything about the guts of LTO, but to me that suggests a
bug in its unification of function decls, rather than a bug in dead-code
removal.