Re: GCC 4.4.0-rc1 available

[Dave Korn <dave dot korn dot cygwin at googlemail dot com>]

H.J. Lu wrote:
> On Wed, Apr 15, 2009 at 6:49 AM, Dave Korn 
> <dave.korn.cygwin@googlemail.com> wrote:
>> Jakub Jelinek wrote:
>>> GCC 4.4.0 release candidate 1 is now available at:
>>> 
>>> ftp://gcc.gnu.org/pub/gcc/snapshots/4.4.0-RC-20090414/
>>> 
>>> Please test the tarballs there and report any problems to Bugzilla.  CC
>>> me on the bugs if you believe they are regressions from previous
>>> releases severe enough that they should block the 4.4.0 release.
>> My testsuite run is still only part-way through, and I'll file PRs when
>> it's complete, but I just wanted to flag this up: I'm seeing a lot of
>> failures related to stack alignment and vectorisation.
>> 
>> All the FAILs that I've examined so far turn out to be misaligned
>> addresses in SSE2 instructions resulting in SIGILL at runtime.
>> 
>> For instance: gcc.dg/torture/stackalign/push-1.c compiles to have this
>> line of assembly:
>> 
>> 0x004011f6 <foo+59>:    movaps %xmm0,0x404024
>> 
>> I tried the same testcase with 4.3.2, and it also fails, but for a
>> different reason.  The testcase uses "-mpreferred-stack-boundary=2", and
>> without that option it still fails with 4.4.0rc1 but passes with 4.3.2.
>> 
> 
> Gcc 4.4 tests are OK on Linux/i686. Gcc should align stack automatically. 
> Please include the assembly outputs for any stack alignment related bug 
> reports.

  Sure, although in this particular testcase it's not stack alignment but
.data section objects.  (I think the stack alignment is probably working;
that's what causes the "fails, but for a different reason" with 4.3.2, it's a
failure in main() where the stack isn't aligned.  This doesn't happen with
4.4.0, but I still get the unaligned access).

  The push-1.c testcase has:

__m128 r;

void
__attribute__ ((noinline))
foo (__m128 x, __m128 y ,__m128 z ,__m128 a, int size)
{
  aligned i;

  if (size != 5 || check_int (&i, __alignof__(i)) != i)
    abort ();

  r = a;
}

and it fails on the assignment "r = a;" because r is unaligned (0x404024); in
the assembly source, it is simply defined as

	.comm	_r, 16	 # 16

so maybe the problem is in the Cygwin linker script?  Is the COMMON section
supposed to be aligned?  In Cygwin, it just gets appended into .bss, like so:

 .bss           0x00404024        0x0
/gnu/gcc/releases/4.4.0rc1/gcc/libgcc.a(_ctors.o)
 .bss           0x00404024        0x0 /gnu/gcc/releases/4.4.0rc1/gcc/crtend.o
 *(COMMON)
 COMMON         0x00404024       0x10
/win/c/DOCUME~1/ADMINI~1/LOCALS~1/Temp/cc86uXzW.o
                0x00404024                _r
 COMMON         0x00404034       0x20
/gnu/gcc/releases/4.4.0rc1/gcc/libgcc.a(_ctors.o)
                0x00404054                __bss_end__ = .

  Does there need to be an alignment specified for COMMON (and/or other
sections)?

    cheers,
      DaveK