The following commit has been merged into the x86/asm branch of tip:
Commit-ID: 4c9a93800121e90484cd07c8e5bde70e31cdb996
Gitweb: https://git.kernel.org/tip/4c9a93800121e90484cd07c8e5bde70e31cdb996
Author: Alexey Dobriyan <adobriyan@xxxxxxxxx>
AuthorDate: Thu, 14 Mar 2024 19:57:15 +03:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 22 Mar 2024 11:47:34 +01:00
x86/asm/64: Clean up memset16(), memset32(), memset64() assembly constraints in <asm/string_64.h>
- Use "+" constraint modifier,
simplify inputs and output lists,
delete dummy variables with meaningless names,
"&" only makes sense in complex assembly creating constraints on
intermediate registers. But 1 instruction assemblies don't have
inner body so to speak.
- Write "rep stos*" on one line:
Rep prefix is integral part of x86 instruction. I'm not sure why
people separate "rep" with newline.
Uros Bizjak adds context: "some archaic assemblers rejected 'rep
insn' on one line. I have checked that the minimum required
binutils-2.25 assembles this without problems."
- Use __auto_type for maximum copy pasta experience,
- Reformat a bit to make everything looks nicer.
Note that "memory" clobber is too much if "n" is known at compile time.
However,
"=m" (*(T(*)[n])s)
doesn't work because -Wvla even if "n" is compile time constant:
if (BCP(n)) {
rep stos
: "=m" (*(T(*)[n])s)
} else {
rep stosw
: "memory"
}
The above doesn't work.
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Link: https://lore.kernel.org/r/20240314165715.31831-1-adobriyan@xxxxxxxxx
---
arch/x86/include/asm/string_64.h | 45 ++++++++++++++++---------------
1 file changed, 24 insertions(+), 21 deletions(-)
diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 857d364..9d0b324 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -30,37 +30,40 @@ void *__memset(void *s, int c, size_t n);
#define __HAVE_ARCH_MEMSET16
static inline void *memset16(uint16_t *s, uint16_t v, size_t n)
{
- long d0, d1;
- asm volatile("rep\n\t"
- "stosw"
- : "=&c" (d0), "=&D" (d1)
- : "a" (v), "1" (s), "0" (n)
- : "memory");
- return s;
+ const __auto_type s0 = s;
+ asm volatile (
+ "rep stosw"
+ : "+D" (s), "+c" (n)
+ : "a" (v)
+ : "memory"
+ );
+ return s0;
}
#define __HAVE_ARCH_MEMSET32
static inline void *memset32(uint32_t *s, uint32_t v, size_t n)
{
- long d0, d1;
- asm volatile("rep\n\t"
- "stosl"
- : "=&c" (d0), "=&D" (d1)
- : "a" (v), "1" (s), "0" (n)
- : "memory");
- return s;
+ const __auto_type s0 = s;
+ asm volatile (
+ "rep stosl"
+ : "+D" (s), "+c" (n)
+ : "a" (v)
+ : "memory"
+ );
+ return s0;
}
#define __HAVE_ARCH_MEMSET64
static inline void *memset64(uint64_t *s, uint64_t v, size_t n)
{
- long d0, d1;
- asm volatile("rep\n\t"
- "stosq"
- : "=&c" (d0), "=&D" (d1)
- : "a" (v), "1" (s), "0" (n)
- : "memory");
- return s;
+ const __auto_type s0 = s;
+ asm volatile (
+ "rep stosq"
+ : "+D" (s), "+c" (n)
+ : "a" (v)
+ : "memory"
+ );
+ return s0;
}
#endif
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