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x86: Fix __wcsncmp_avx2 in strcmp-avx2.S [BZ# 28755]

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Fixes [BZ# 28755] for wcsncmp by redirecting length >= 2^56 to
__wcscmp_avx2. For x86_64 this covers the entire address range so any
length larger could not possibly be used to bound `s1` or `s2`.

test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
(cherry picked from commit ddf0992cf5)
This commit is contained in:
Noah Goldstein 2022-01-09 16:02:21 -06:00 committed by H.J. Lu
parent 646ec4ebe5
commit be6fb78a1f
1 changed files with 10 additions and 0 deletions
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10
sysdeps/x86_64/multiarch/strcmp-avx2.S
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@ -83,6 +83,16 @@ ENTRY (STRCMP)
je L(char0)
jb L(zero)
# ifdef USE_AS_WCSCMP
# ifndef __ILP32__
movq %rdx, %rcx
/* Check if length could overflow when multiplied by
sizeof(wchar_t). Checking top 8 bits will cover all potential
overflow cases as well as redirect cases where its impossible to
length to bound a valid memory region. In these cases just use
'wcscmp'. */
shrq $56, %rcx
jnz __wcscmp_avx2
# endif
/* Convert units: from wide to byte char. */
shl $2, %RDX_LP
# endif