Re: c/4391: memcpy(buf, base, len); defunction compiling bind with -O2

[Graham Stott <grahams@redhat.com>]

The following reply was made to PR c/4391; it has been noted by GNATS.

From: Graham Stott <grahams@redhat.com>
To: georg.wild@gmx.de
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c/4391: memcpy(buf, base, len); defunction compiling bind with -O2
Date: Tue, 25 Sep 2001 18:10:17 +0700

 georg.wild@gmx.de wrote:
 > 
 > >Number:         4391
 > >Category:       c
 > >Synopsis:       memcpy(buf, base, len); defunction compiling bind with -O2
 > >Confidential:   no
 > >Severity:       serious
 > >Priority:       medium
 > >Responsible:    unassigned
 > >State:          open
 > >Class:          sw-bug
 > >Submitter-Id:   net
 > >Arrival-Date:   Tue Sep 25 03:36:01 PDT 2001
 > >Closed-Date:
 > >Last-Modified:
 > >Originator:     georg.wild@gmx.de
 > >Release:        latest cvs snapshot
 > >Organization:
 > >Environment:
 > i686-pc-linux-gnu linux 2.2.19 glibc 2.2.4 and mostly newest libraries
 > >Description:
 > Sorry, but it was not possible for me producing a compilable example because this bug is somehow connected with libraries and .....! Therefore I'll describe what happens!
 
 > It occurs compiling ftp://ftp.isc.org/isc/bind9/9.2.0rc4/bind-9.2.0rc4.tar.gz and specially libisc.
 > The position where it is first seen in the main program is in:
 > isc_result_t
 > isc_file_progname(const char *filename, char *buf, size_t buflen) {
 >         const char *base;
 >         size_t len;
 > 
 >         REQUIRE(filename != NULL);
 >         REQUIRE(buf != NULL);
 > 
 >         base = isc_file_basename(filename);
 >         len = strlen(base) + 1;
 > 
 >         if (len > buflen)
 >                 return (ISC_R_NOSPACE);
 >         memcpy(buf, base, len);
 > 
 >         return (ISC_R_SUCCESS);
 > }
 > When reaching the memcpy line, I see in ddd the program returning to the main program without setting ISC_R_SUCCESS. In the asm tab there is a jmp-Funktion. Pressing next in machine code returns directly to the main program!
 
 I recognize this bug :-) the compiler is incorrectly translating the memcpy call as a sibcall and hence the return ISC_R_SUCCESS
 is never executed.
 
 Try the following patch which I'll commit to CVS shortly
 
 ChangeLog
 
         *sibcall.c (skip_copy_to_return_value): Tighten return value
         copy check.
 
 -------------------------------------------------------------------
 Index: sibcall.c
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/sibcall.c,v
 retrieving revision 1.24
 diff -c -p -r1.24 sibcall.c
 *** sibcall.c   2001/08/22 14:35:42     1.24
 --- sibcall.c   2001/09/09 15:52:37
 *************** skip_copy_to_return_value (orig_insn)
 *** 159,166 ****
 
     if (return_value_pseudo)
       {
 !       if (SET_DEST (set) == return_value_pseudo)
 !         return insn;
         return orig_insn;
       }
 
 --- 159,167 ----
 
     if (return_value_pseudo)
       {
 !       if (SET_DEST (set) == return_value_pseudo
 !         && SET_SRC (set) == softret)
 !       return insn;
         return orig_insn;
       }
 
 ---------------------------------------------------------------------
 
 
 Graham