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Make memcmp() and memchr() go fast again

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Readahead within the specified size is legal, even if it overlaps a page
boundary; it's the fault of the caller if that causes a segfault.
This commit is contained in:
Justine Tunney 2023-11-29 05:17:21 -08:00
parent 70155df7a9
commit ff955aaa01
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GPG key ID: BE714B4575D6E328
4 changed files with 137 additions and 49 deletions
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15
test/libc/intrin/memcmp_test.c
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@ -113,21 +113,6 @@ TEST(memcmp, fuzz) {
}
}
TEST(memcmp, pageOverlapTorture) {
long pagesz = sysconf(_SC_PAGESIZE);
char *map = mmap(0, pagesz * 2, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
char *map2 = mmap(0, pagesz * 2, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
ASSERT_SYS(0, 0, mprotect(map + pagesz, pagesz, PROT_NONE));
ASSERT_SYS(0, 0, mprotect(map2 + pagesz, pagesz, PROT_NONE));
strcpy(map + pagesz - 9, "12345678");
strcpy(map2 + pagesz - 9, "12345679");
EXPECT_LT(memcmp(map + pagesz - 9, map2 + pagesz - 9, 79), 0);
EXPECT_SYS(0, 0, munmap(map2, pagesz * 2));
EXPECT_SYS(0, 0, munmap(map, pagesz * 2));
}
int buncmp(const void *, const void *, size_t) asm("bcmp");
int funcmp(const void *, const void *, size_t) asm("memcmp");