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Re: g++ 3.4.0 cygwin, codegen SSE & alignement issues


On Wed, Apr 28, 2004 at 02:30:47PM -0500, Brian Ford wrote:
>On Wed, 28 Apr 2004, Christopher Faylor wrote:
>
>> On Wed, Apr 28, 2004 at 12:41:51PM -0500, Brian Ford wrote:
>> This patch would only affect non-main threads.  It would not affect the
>> main thread.  Wouldn't you need to do the same thing for the main thread?
>> I don't understand why it would be different.
>
>Something already does.  I didn't try and track down the what/why.
>
>00401060 <_main>:
>   401060:       55                      push   %ebp
>   401061:       b8 10 00 00 00          mov    $0x10,%eax
>   401066:       89 e5                   mov    %esp,%ebp
>   401068:       83 ec 08                sub    $0x8,%esp
>   40106b:       83 e4 f0                and    $0xfffffff0,%esp <-- SEE
>
>This problem doesn't happen for the main thread.  I'll try to pin the who
>down if you like.

Nope.  It must be happening in crt0.c.

This patch looks reasonable (although I wonder at the need for
__builtin_return_address(1)).

Interestingly enough, this wouldn't have been generically fixable prior
to Cygwin 1.5.6.

cgf

>> >2004-04-28  DJ Delorie  <dj@redhat.com>
>> >
>> >        * init.cc (threadfunc_fe): Hack to make thread stacks always 16
>> >	byte aligned.
>> >
>> >Index: init.cc
>> >===================================================================
>> >RCS file: /cvs/src/src/winsup/cygwin/init.cc,v
>> >retrieving revision 1.32
>> >diff -u -p -r1.32 init.cc
>> >--- init.cc     22 Mar 2004 18:30:38 -0000      1.32
>> >+++ init.cc     28 Apr 2004 17:38:03 -0000
>> >@@ -27,6 +27,8 @@ HANDLE sync_startup;
>> > static void WINAPI
>> > threadfunc_fe (VOID *arg)
>> > {
>> >+  (void)__builtin_return_address(1);
>> >+  asm volatile ("andl $-16,%%esp" ::: "%esp");
>> >   _cygtls::call ((DWORD (*)  (void *, void *)) (((char **)
>> >_tlsbase)[OLDFUNC_OFFSET]), arg);
>> > }
>
>-- 
>Brian Ford
>Senior Realtime Software Engineer
>VITAL - Visual Simulation Systems
>FlightSafety International
>the best safety device in any aircraft is a well-trained pilot...
>
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