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GCC 3.4 miscompiles memrchr (the testsuite fails). The GCC developers closed my bugs as invalid: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=9196 with the following comment: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The C semantics for pointer arithmetic mean that GCC is allowed to assume that this line return __res + 1; never causes a null pointer to be returned. The "mis-optimized" code has been optimized based on that assumption. In short, the bug is in glibc. The simplest fix is to write "incl %0" as the last instruction of the assembly block rather than trying to do this calculation in C. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here's a patch for this, ok to commit? Andreas 2003-09-04 Andreas Jaeger <aj@suse.de> * sysdeps/i386/bits/string.h (__memrchr): Do addition in assembler to make it conforming C. * sysdeps/i386/i486/bits/string.h (__memrchr): Likewise. ============================================================ Index: sysdeps/i386/bits/string.h --- sysdeps/i386/bits/string.h 6 Jul 2001 04:55:53 -0000 1.21 +++ sysdeps/i386/bits/string.h 4 Sep 2003 10:05:12 -0000 @@ -1,5 +1,5 @@ /* Optimized, inlined string functions. i386 version. - Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation, Inc. + Copyright (C) 1997,1998,1999,2000,2003 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or @@ -321,11 +321,12 @@ __memrchr (__const void *__s, int __c, s "repne; scasb\n\t" "je 1f\n\t" "orl $-1,%0\n" - "1:\tcld" + "1:\tcld\n\t" + "incl %0" : "=D" (__res), "=&c" (__d0) : "a" (__c), "0" (__s + __n - 1), "1" (__n) : "cc"); - return __res + 1; + return __res; } # ifdef __USE_GNU # define memrchr(s, c, n) __memrchr (s, c, n) ============================================================ Index: sysdeps/i386/i486/bits/string.h --- sysdeps/i386/i486/bits/string.h 14 Jan 2003 07:44:02 -0000 1.55 +++ sysdeps/i386/i486/bits/string.h 4 Sep 2003 10:05:12 -0000 @@ -484,7 +484,8 @@ __memrchr (__const void *__s, int __c, s ("std\n\t" "repne; scasb\n\t" "cmovne %2,%0\n\t" - "cld" + "cld\n\t" + "incl %0" : "=D" (__res), "=&c" (__d0), "=&r" (__d1) : "a" (__c), "0" (__s + __n - 1), "1" (__n), "2" (-1), "m" ( *(struct { __extension__ char __x[__n]; } *)__s) @@ -495,13 +496,14 @@ __memrchr (__const void *__s, int __c, s "repne; scasb\n\t" "je 1f\n\t" "orl $-1,%0\n" - "1:\tcld" + "1:\tcld\n\t" + "incl %0" : "=D" (__res), "=&c" (__d0) : "a" (__c), "0" (__s + __n - 1), "1" (__n), "m" ( *(struct { __extension__ char __x[__n]; } *)__s) : "cc"); # endif - return __res + 1; + return __res; } # ifdef __USE_GNU # define memrchr(s, c, n) __memrchr ((s), (c), (n)) -- Andreas Jaeger, aj@suse.de, http://www.suse.de/~aj SuSE Linux AG, Deutschherrnstr. 15-19, 90429 Nürnberg, Germany GPG fingerprint = 93A3 365E CE47 B889 DF7F FED1 389A 563C C272 A126
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