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Avoid undefined behaviour in ibm128 implementation of llroundl (BZ #29488)

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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)
This commit is contained in:
Aurelien Jarno 2022-10-10 00:39:33 +02:00
parent b357157361
commit 9273b2d0e9
2 changed files with 11 additions and 12 deletions
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2
NEWS
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@ -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

21
sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
View File

@ -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