Re: pkg/47906: lang/g95: SEGV occurs when stack address is not aligned 8 bytes at main().

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

The following reply was made to PR pkg/47906; it has been noted by GNATS.

From: Joerg Sonnenberger <joerg%britannica.bec.de@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: pkg/47906: lang/g95: SEGV occurs when stack address is not
 aligned 8 bytes at main().
Date: Tue, 9 Jul 2013 15:02:08 +0200

 On Tue, Jul 09, 2013 at 12:50:01PM +0000, NONAKA Kimihiro wrote:
 > The following reply was made to PR pkg/47906; it has been noted by GNATS.
 > 
 > From: NONAKA Kimihiro <nonakap%gmail.com@localhost>
 > To: gnats-bugs%netbsd.org@localhost
 > Cc: wennmach%netbsd.org@localhost, gnats-admin%netbsd.org@localhost, 
 > pkgsrc-bugs%netbsd.org@localhost
 > Subject: Re: pkg/47906: lang/g95: SEGV occurs when stack address is not
 >  aligned 8 bytes at main().
 > Date: Tue, 9 Jul 2013 21:46:03 +0900
 > 
 >  Hi,
 >  
 >  2013/7/9 Joerg Sonnenberger <joerg%britannica.bec.de@localhost>:
 >  
 >  >  > >Description:
 >  >  > If the stack address is not aligned on 8 bytes, it is adjusted to 8 
 > bytes aligned at main().
 >  >  > If stack address is adjusted, to get from the stack address the wrong 
 > return address, SEGV occurs.
 >  >
 >  >  What happens if the whole section is dropped, i.e. the stack pointer
 >  >  isn't adjusted in main at all? It shouldn't be needed at nothing on x86
 >  >  requires 64bit alignment.
 >  
 >  for speed.
 >  
 >  g95-0.93/libf95.a-0.93/runtime/main.c:
 >  
 >   46 int main(int argc, char *argv[]) {
 >   47
 >   48 /* Sometimes on x86, the stack isn't aligned to an 8-byte boundary,
 >   49  * which kills performance associated with doubles.  Align if
 >   50  * unaligned. */
 >   51
 >   52 #if HAVE_REAL_10 == 1 || HAVE_REAL_10 == 2
 >   53     asm("mov %%esp, %%eax\n"
 >   54         "and $0x04, %%eax\n"
 >   55         "sub %%eax, %%esp\n" : : : "%eax");
 >   56 #endif
 
 I don't beliebe that comment is true, I was more asking whether it just
 works...
 
 Joerg