[Bug libc/18447] New: memstream.c:92 dereferencing type-punned pointer -Werror=strict-aliasing

[Bug libc/18447] New: memstream.c:92 dereferencing type-punned pointer -Werror=strict-aliasing

[darlingm at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18447

            Bug ID: 18447
           Summary: memstream.c:92 dereferencing type-punned pointer
                    -Werror=strict-aliasing
           Product: glibc
           Version: 2.21
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: darlingm at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Under gcc trunk (6.0.0, 20150521):

In file included from memstream.c:18:0:
memstream.c: In function `open_memsteam':
memstream.c:92:22: error: dereferencing type-punned pointer will break
strict-aliasing rules [-Werror=strict-aliasing]
   _IO_JUMPS ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf) = &_IO_mem_jumps;

libioP.h:107:26: note: in definition of macro `_IO_JUMPS`
 #define _IO_JUMPS(THIS) (THIS)->vtable

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[Bug libc/18447] memstream.c:92 dereferencing type-punned pointer -Werror=strict-aliasing

[darlingm at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18447

--- Comment #1 from darlingm at gmail dot com ---
Attempted a temporary workaround of configure
CFLAGS="-Wno-error=strict-aliasing", which errored saying "glibc cannot be
compiled without optimization"

Tried CFLAGS="-Wno-error=strict-aliasing -fno-strict-aliasing" with the same
error.

Ran across that these cflags conflict with -O2, and was able to get past it by
using CFLAGS="-Wno-error=strict-aliasing -fno-strict-aliasing -O2"

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[Bug libc/18447] memstream.c:92 dereferencing type-punned pointer -Werror=strict-aliasing

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18447

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |2.22

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
Fixed by e69dcccbcb53b2c0f3fbe3f6c3e04aadae7e9265.

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