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From: "hjl.tools at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug string/25933] Off by one error in __strncmp_avx2 when
 length=VEC_SIZE*4 and strings are at page boundaries can cause a segfault
Date: Sun, 07 Jun 2020 18:30:45 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25933

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Sunil Pandey from comment #4)
> Created attachment 12601 [details]
> strncmp_avx2 patch for pr25933
>=20
> Tested attached patch on
>=20
> https://gitlab.com/x86-glibc/glibc/-/commits/users/hjl/pr25933/master

Looks good.  Please try this

diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S
b/sysdeps/x86_64/multiarch/strcmp-avx2.S
index 48d03a9f46..dabc3e7590 100644
--- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
+++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
@@ -256,6 +256,11 @@ L(next_3_vectors):
   vpmovmskb %ymm0, %ecx
   testl %ecx, %ecx
   jne   L(return_3_vec_size)
+# ifdef USE_AS_STRNCMP
+  /* Check if VEC_SIZE * 4 already exceeded max compare count %r11 */
+  cmpq  $(VEC_SIZE * 4), %r11
+  jbe   L(zero)
+# endif
 L(main_loop_header):
   leaq  (VEC_SIZE * 4)(%rdi), %rdx
   movl  $PAGE_SIZE, %ecx

--=20
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