target/9506: ABI breakage: structure return

target/9506: ABI breakage: structure return

[Gerald Pfeifer]

>Number:         9506
>Category:       target
>Synopsis:       ABI breakage: structure return
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jan 30 13:56:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     
>Release:        3.4 20030130 (experimental)
>Organization:
>Environment:
System: FreeBSD naos.dbai.tuwien.ac.at 4.7-RELEASE FreeBSD 4.7-RELEASE #0: Thu Jan 9 09:25:29 CET 2003 root@aludra.dbai.tuwien.ac.at:/usr/src/sys/compile/DBAI-MP i386

host: i386-unknown-freebsd4.7
build: i386-unknown-freebsd4.7
target: i386-unknown-freebsd4.7
configured with: /sw/test/gcc/cvs/configure --prefix=/sw/gcc-current --enable-languages=c,c++ --disable-checking
>Description:
	Unless I am completely mistaken, the following patch is responsible for an
	ABI change I am seeing on FreeBSD (and apparently also Cygwin, Interix,
	OpenBSD, NetBSD) on i386 platforms for GCC 3.2.1 as well as the 3.3 branch
	and mainline:

	Thu Oct 31 18:08:00 CET 2002  Jan Hubicka  <jh@suse.cz>

	  * i386.c (override_options): Set defaults for flag_omit_frame_pointer,
	  flag_asynchronous_unwind_tables, flag_pcc_struct_return.
	  * i386.c (optimization_options): Set flag_omit_frame_pointer,
	  flag_asynchronous_unwind_tables, flag_pcc_struct_return to 2.
	  Do not clear -momit-leaf-frame-pointer when profiling.
	  (ix86_frame_pointer_required): Frame pointer is always required when
	  profiling.

	http://gcc.gnu.org/ml/gcc-patches/2002-10/msg01887.html

>How-To-Repeat:
	#include <stdio.h>
	#include <stdlib.h>
 
	int main() {
	  div_t d = div(20,5);
 
	  printf("20/5 = %d mod %d\n",d.quot,d.rem);
	}

	will print something different from "20/5 = 4 mod 0".
>Fix:
	What I believe is wrong with this patch is that it _completely_ ignores
	DEFAULT_PCC_STRUCT_RETURN when setting flag_pcc_struct_return:

	  gcc/config/i386% grep DEFAULT_PCC_STRUCT_RETURN *.h | wc -l
	  19
	  gcc/config/i386% grep DEFAULT_PCC_STRUCT_RETURN i386.c | wc -l
	  0
>Release-Note:
>Audit-Trail:
>Unformatted: