* [COMMITTED 2.36] Avoid undefined behaviour in ibm128 implementation of llroundl (BZ #29488)
@ 2022-10-24 18:58 Aurelien Jarno
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From: Aurelien Jarno @ 2022-10-24 18:58 UTC (permalink / raw)
To: libc-stable; +Cc: Aurelien Jarno, Tulio Magno Quites Machado Filho
Detecting an overflow edge case depended on signed overflow of a long
long. Replace the additions and the overflow checks by
__builtin_add_overflow().
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
(cherry picked from commit 2b5478569e72ee4820a6e163d306690c9c0eaf5e)
---
NEWS | 2 ++
sysdeps/ieee754/ldbl-128ibm/s_llroundl.c | 21 +++++++++------------
2 files changed, 11 insertions(+), 12 deletions(-)
diff --git a/NEWS b/NEWS
index a6da588c85..8c60d3dc8d 100644
--- a/NEWS
+++ b/NEWS
@@ -33,6 +33,8 @@ The following bugs are resolved with this release:
[29485] Linux: Terminate subprocess on late failure in tst-pidfd
[29490] alpha: New __brk_call implementation is broken
[29463] math/test-float128-y1 fails on x86_64
+ [29488] test-ibm128-llround fails on ppc64el when built with gcc-12 and -O2
+ or higher
[29528] elf: Call __libc_early_init for reused namespaces
[29537] libc: [2.34 regression]: Alignment issue on m68k when using
[29539] libc: LD_TRACE_LOADED_OBJECTS changed how vDSO library are
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c b/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
index d85154e73a..d8c0de1faf 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
@@ -66,38 +66,35 @@ __llroundl (long double x)
/* Peg at max/min values, assuming that the above conversions do so.
Strictly speaking, we can return anything for values that overflow,
but this is more useful. */
- res = hi + lo;
-
- /* This is just sign(hi) == sign(lo) && sign(res) != sign(hi). */
- if (__glibc_unlikely (((~(hi ^ lo) & (res ^ hi)) < 0)))
+ if (__glibc_unlikely (__builtin_add_overflow (hi, lo, &res)))
goto overflow;
xh -= lo;
ldbl_canonicalize (&xh, &xl);
- hi = res;
if (xh > 0.5)
{
- res += 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, 1, &res)))
+ goto overflow;
}
else if (xh == 0.5)
{
if (xl > 0.0 || (xl == 0.0 && res >= 0))
- res += 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, 1, &res)))
+ goto overflow;
}
else if (-xh > 0.5)
{
- res -= 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, -1, &res)))
+ goto overflow;
}
else if (-xh == 0.5)
{
if (xl < 0.0 || (xl == 0.0 && res <= 0))
- res -= 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, -1, &res)))
+ goto overflow;
}
- if (__glibc_unlikely (((~(hi ^ (res - hi)) & (res ^ hi)) < 0)))
- goto overflow;
-
return res;
}
else
--
2.35.1
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