Date: Thu, 29 Jul 2021 04:01:07 GMT From: Conrad Meyer <cem@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 7f8f79a5c444 - main - libc qsort(3): Eliminate ambiguous sign comparison Message-ID: <202107290401.16T417WC099165@gitrepo.freebsd.org>
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The branch main has been updated by cem: URL: https://cgit.FreeBSD.org/src/commit/?id=7f8f79a5c444a565a32b0c6578b07f8d496f6c49 commit 7f8f79a5c444a565a32b0c6578b07f8d496f6c49 Author: Conrad Meyer <cem@FreeBSD.org> AuthorDate: 2021-07-23 18:04:21 +0000 Commit: Conrad Meyer <cem@FreeBSD.org> CommitDate: 2021-07-29 03:59:20 +0000 libc qsort(3): Eliminate ambiguous sign comparison The left side of the MIN() expression is the (signed) result of pointer subtraction (ptrdiff_t). The right hand side is the also the (signed) result of pointer subtraction, additionally subtracting the element size ('es'), which is unsigned size_t. This coerces the right-hand expression into an unsigned value. MIN(signed, unsigned) triggers -Wsign-compare. Sorting elements of size greater than SSIZE_MAX is nonsensical, so we can instead treat the element size as ssize_t, leaving the right-hand result the same signedness as the left. Reviewed by: arichardson, kib Differential Revision: https://reviews.freebsd.org/D31292 --- lib/libc/stdlib/Makefile.inc | 2 ++ lib/libc/stdlib/qsort.c | 7 ++++++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/libc/stdlib/Makefile.inc b/lib/libc/stdlib/Makefile.inc index de8d8484e135..361761e73fdd 100644 --- a/lib/libc/stdlib/Makefile.inc +++ b/lib/libc/stdlib/Makefile.inc @@ -18,6 +18,8 @@ MISRCS+=C99_Exit.c a64l.c abort.c abs.c atexit.c atof.c atoi.c atol.c atoll.c \ strtol.c strtold.c strtoll.c strtoq.c strtoul.c strtonum.c strtoull.c \ strtoumax.c strtouq.c system.c tdelete.c tfind.c tsearch.c twalk.c +CFLAGS.qsort.c+= -Wsign-compare + # Work around an issue on case-insensitive file systems. # libc has both _Exit.c and _exit.s and they both yield # _exit.o (case insensitively speaking). diff --git a/lib/libc/stdlib/qsort.c b/lib/libc/stdlib/qsort.c index cfd2d99025f0..5016fff7895f 100644 --- a/lib/libc/stdlib/qsort.c +++ b/lib/libc/stdlib/qsort.c @@ -171,7 +171,12 @@ loop: pn = (char *)a + n * es; d1 = MIN(pa - (char *)a, pb - pa); vecswap(a, pb - d1, d1); - d1 = MIN(pd - pc, pn - pd - es); + /* + * Cast es to preserve signedness of right-hand side of MIN() + * expression, to avoid sign ambiguity in the implied comparison. es + * is safely within [0, SSIZE_MAX]. + */ + d1 = MIN(pd - pc, pn - pd - (ssize_t)es); vecswap(pb, pn - d1, d1); d1 = pb - pa;
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