Date: Thu, 28 Dec 2023 17:20:15 GMT From: Robert Clausecker <fuz@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: cec0236976cd - stable/14 - lib/libc/amd64/string/strcspn.S: always return earliest match in 17--32 char case Message-ID: <202312281720.3BSHKFE6080732@gitrepo.freebsd.org>
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The branch stable/14 has been updated by fuz: URL: https://cgit.FreeBSD.org/src/commit/?id=cec0236976cd0cce0c7c05b1031b7f4215ce9178 commit cec0236976cd0cce0c7c05b1031b7f4215ce9178 Author: Robert Clausecker <fuz@FreeBSD.org> AuthorDate: 2023-12-19 17:28:57 +0000 Commit: Robert Clausecker <fuz@FreeBSD.org> CommitDate: 2023-12-28 17:02:41 +0000 lib/libc/amd64/string/strcspn.S: always return earliest match in 17--32 char case When matching against a set of 17--32 characters, strcspn() uses two invocations of PCMPISTRI to match against the first 16 characters of the set and then the remaining characters. If a match was found in the first half of the set, the code originally immediately returned that match. However, it is possible for a match in the second half of the set to occur earlier in the vector, leading to that match being overlooked. Fix the code by checking if there is a match in the second half of the set and taking the earlier of the two matches. The correctness of the function has been verified with extended unit tests and test runs against the glibc test suite. Approved by: mjg (implicit, via IRC) MFC after: 1 week MFC to: stable/14 (cherry picked from commit c91cd7d03a9dee649ba3a1b9b4014df9de111bb8) --- lib/libc/amd64/string/strcspn.S | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) diff --git a/lib/libc/amd64/string/strcspn.S b/lib/libc/amd64/string/strcspn.S index 53100eeea9a5..648635529e5b 100644 --- a/lib/libc/amd64/string/strcspn.S +++ b/lib/libc/amd64/string/strcspn.S @@ -255,19 +255,28 @@ ARCHENTRY(strcspn, x86_64_v2) leave ret + /* match in first set half during head */ +.Lheadmatchv2first: + mov %ecx, %eax + pcmpistri $0, %xmm0, %xmm3 # match in second set half? + cmp %ecx, %eax # before the first half match? + cmova %ecx, %eax # use the earlier match + leave + ret + .Lgt16v2: movdqu 48(%rsp, %rcx, 1), %xmm3 # second part of set /* set is 17--32 bytes in size */ pcmpistri $0, %xmm0, %xmm2 # match in first set half? - jb .Lheadmatchv2 + jb .Lheadmatchv2first pcmpistri $0, %xmm0, %xmm3 # match in second set half or end of string? jbe .Lheadmatchv2 ALIGN_TEXT 0: movdqa (%rax), %xmm0 pcmpistri $0, %xmm0, %xmm2 - jb 2f # match in first set half? + jb 4f # match in first set half? pcmpistri $0, %xmm0, %xmm3 jbe 1f # match in second set half or end of string? movdqa 16(%rax), %xmm0 @@ -277,7 +286,8 @@ ARCHENTRY(strcspn, x86_64_v2) pcmpistri $0, %xmm0, %xmm3 ja 0b # neither match in 2nd half nor string end? -3: lea -16(%rax), %rax # go back to second half + /* match in second half or NUL */ + lea -16(%rax), %rax # go back to second half 1: jc 2f # jump if match found pxor %xmm1, %xmm1 pcmpeqb %xmm1, %xmm0 # where is the NUL byte? @@ -288,6 +298,17 @@ ARCHENTRY(strcspn, x86_64_v2) leave ret + /* match in first half */ +3: sub $16, %rax # go back to second half +4: sub %rdi, %rax # offset of %xmm0 from beginning of string + mov %ecx, %edx + pcmpistri $0, %xmm0, %xmm3 # match in second set half? + cmp %ecx, %edx # before the first half match? + cmova %ecx, %edx # use the earlier match + add %rdx, %rax # return full ofset + leave + ret + /* set is empty, degrades to strlen */ .Lstrlenv2: leave
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