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authorConrad Meyer <cem@FreeBSD.org>2021-07-23 18:04:21 +0000
committerConrad Meyer <cem@FreeBSD.org>2021-07-29 03:59:20 +0000
commit7f8f79a5c444a565a32b0c6578b07f8d496f6c49 (patch)
tree44bb86dccb1247513cf6a668d53564566ed934a5 /lib/libc
parente3707726c168eeb0ba06d13873dd71590b77d604 (diff)
downloadsrc-7f8f79a5c444a565a32b0c6578b07f8d496f6c49.tar.gz
src-7f8f79a5c444a565a32b0c6578b07f8d496f6c49.zip
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
Diffstat (limited to 'lib/libc')
-rw-r--r--lib/libc/stdlib/Makefile.inc2
-rw-r--r--lib/libc/stdlib/qsort.c7
2 files changed, 8 insertions, 1 deletions
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;