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Message-Id: <20230830135726.1939997-4-ammarfaizi2@gnuweeb.org>
Date: Wed, 30 Aug 2023 20:57:24 +0700
From: Ammar Faizi <ammarfaizi2@...weeb.org>
To: Willy Tarreau <w@....eu>,
Thomas Weißschuh <linux@...ssschuh.net>
Cc: Ammar Faizi <ammarfaizi2@...weeb.org>,
Nicholas Rosenberg <inori@...x.org>,
Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
Michael William Jonathan <moe@...weeb.org>,
GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH v1 3/5] tools/nolibc: x86-64: Use `rep cmpsb` for `memcmp()`
Simplify memcmp() on the x86-64 arch.
The x86-64 arch has a 'rep cmpsb' instruction, which can be used to
implement the memcmp() function.
%rdi = source 1
%rsi = source 2
%rcx = length
Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
---
tools/include/nolibc/arch-x86_64.h | 19 +++++++++++++++++++
tools/include/nolibc/string.h | 2 ++
2 files changed, 21 insertions(+)
diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h
index 42f2674ad1ecdd64..6c1b54ba9f774e7b 100644
--- a/tools/include/nolibc/arch-x86_64.h
+++ b/tools/include/nolibc/arch-x86_64.h
@@ -214,4 +214,23 @@ __asm__ (
"retq\n"
);
+#define NOLIBC_ARCH_HAS_MEMCMP
+static int memcmp(const void *s1, const void *s2, size_t n)
+{
+ const unsigned char *p1 = s1;
+ const unsigned char *p2 = s2;
+
+ if (!n)
+ return 0;
+
+ __asm__ volatile (
+ "rep cmpsb"
+ : "+D"(p2), "+S"(p1), "+c"(n)
+ : "m"(*(const unsigned char (*)[n])s1),
+ "m"(*(const unsigned char (*)[n])s2)
+ );
+
+ return p1[-1] - p2[-1];
+}
+
#endif /* _NOLIBC_ARCH_X86_64_H */
diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 1bad6121ef8c4ab5..3c941289d5dd0985 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -15,6 +15,7 @@ static void *malloc(size_t len);
* As much as possible, please keep functions alphabetically sorted.
*/
+#ifndef NOLIBC_ARCH_HAS_MEMCMP
static __attribute__((unused))
int memcmp(const void *s1, const void *s2, size_t n)
{
@@ -26,6 +27,7 @@ int memcmp(const void *s1, const void *s2, size_t n)
}
return c1;
}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMCMP */
static __attribute__((unused))
void *_nolibc_memcpy_up(void *dst, const void *src, size_t len)
--
Ammar Faizi
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