Re: target/10395: sse2 datatype is not 16bytes aligned in threaded code

[Vladimir Grebinskiy <vgrebinski@yahoo.com>]

The following reply was made to PR target/10395; it has been noted by GNATS.

From: Vladimir Grebinskiy <vgrebinski@yahoo.com>
To: tprince@computer.org, gcc-gnats@gcc.gnu.org
Cc: vgrebinski@yahoo.com
Subject: Re: target/10395: sse2 datatype is not 16bytes aligned in threaded code
Date: Sun, 13 Apr 2003 18:24:27 -0700 (PDT)

 --- Tim Prince <timothyprince@sbcglobal.net> wrote:
 > On Sunday 13 April 2003 15:44, vgrebinski@yahoo.com wrote:
 > > >Number:         10395
 > > >Category:       target
 > > >Synopsis:       sse2 types are incorrectly aligned causing crash in
 > > > multi-threaded apps Confidential:   no
 > > >Severity:       serious
 > > >Priority:       medium
 > > >Responsible:    unassigned
 > > >State:          open
 > > >Class:          wrong-code
 > > >Submitter-Id:   net
 > > >Arrival-Date:   Sun Apr 13 22:46:00 UTC 2003
 > > >Closed-Date:
 > > >Last-Modified:
 > > >Originator:     Vladimir Grebinskiy
 > > >Release:        3.3 20030410 (prerelease)
 > > >Organization:
 > > >Environment:
 > >
 > > System: Linux vag 2.4.21-pre5 #2 Sun Mar 2 00:28:31 EST 2003 i686 unknown
 > > unknown GNU/Linux Architecture: i686
 > >
 > >
 > > host: i386-pc-linux-gnu
 > > build: i386-pc-linux-gnu
 > > target: i386-pc-linux-gnu
 > > configured with:
 > > /build/packages/gcc/snap/gcc-snapshot-20030410/src/configure -v
 > > --enable-languages=c,c++,java,f77,pascal,objc,ada
 > > --prefix=/usr/lib/gcc-snapshot --infodir=/share/info --mandir=/share/man
 > > --enable-shared --with-system-zlib --enable-nls --without-included-gettext
 > > --enable-__cxa_atexit --enable-clocale=gnu --enable-java-gc=boehm
 > > --enable-java-awt=xlib --with-cpp-install-dir=bin --enable-multilibs
 > > --enable-objc-gc i386-linux
 > >
 > > >Description:
 > >
 > > support for sse2 instruction is an important addtion to gcc-3.3.
 > > Unfortunately, code generated for functions called via pthread_create()
 > > does not provide 16bytes alignment for local sse2 data, which causes crash
 > > when these variables are used.
 > >
 > > >How-To-Repeat:
 > >
 > > The following short program demonstrates problem. The second call to
 > > function "f" shows that variable is not aligned to 16 bytes:
 > >
 > > /* *** start ***/
 > > #include <pthread.h>
 > > #include <stdio.h>
 > > #include <assert.h>
 > >
 > > #include <xmmintrin.h>
 > > #include <mmintrin.h>
 > >
 > > #ifdef __ICC
 > > #include <emmintrin.h>
 > > #endif
 > >
 > > void * f(void *p)
 > > {
 > >   int x = (p == NULL) ? 0 : * (int *) p;
 > >   __m128i s;
 > >   printf("&x = %p &s= %p\n", &x, &s);
 > >   return NULL;
 > > }
 > >
 > > int main(int argc, char ** argv)
 > > {
 > >   pthread_t th;
 > >
 > >   f(& argc);
 > >   assert(pthread_create(& th, NULL, f, &argc)==0);
 > >   assert(pthread_join(th, NULL)==0);
 > >   return 0;
 > > }
 > >
 > > /* ***end *** /
 > >
 > > $ /usr/lib/gcc-snapshot/bin/gcc -pthread -msse2 gcc_test.c -o
 > > gcc_test.LINUX $ ./gcc_test.LINUX
 > > &x = 0xbffffb6c &s= 0xbffffb50
 > > &x = 0xbf7ffae8 &s= 0xbf7ffacc <---- error
 > >
 > > >Fix:
 > >
 > > 
 > Similar problem here, but I had to change --m128i to --m128.  Did you try 
 > rebuilding libpthread with the proper options passed to gcc?  Otherwise, it 
 > looks like an error in the library build.  gcc won't work unless libpthread 
 > passes aligned stack to your function.  I tried another compiler, which 
 > doesn't expect aligned stack, and it was OK.
 
 Thanks for suggestion. I'll try to find out if libpthread should be compiled in a special way (I
 guess whole libc should be recompiled). Currently, all libraries are whatever is in
 Debian/unstable as of today. The code works as expected with Intel's compiler (build 7.1.011), I
 guess it uses the same libpthread as gcc does. 
 
 I just checked that there is a similar problem with MMX datatypes (in which case unaligned access
 is just slower?) -- data are not 8 bytes aligned when called inside a thread (checked also with
 3.2.3 20030407 (Debian prerelease)).
 
 Vladimir
 
 > -- 
 > Tim Prince
 
 
 __________________________________________________
 Do you Yahoo!?
 Yahoo! Tax Center - File online, calculators, forms, and more
 http://tax.yahoo.com