From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: [PATCH 3/7] x86: re-work memset()
Date: Tue, 27 Apr 2021 14:54:24 +0200 [thread overview]
Message-ID: <f976337c-5dec-ddc3-19e8-a0ee4273cd36@suse.com> (raw)
In-Reply-To: <6d6da76c-ccc8-afa2-bd06-5ae132c354f2@suse.com>
Move the function to its own assembly file. Having it in C just for the
entire body to be an asm() isn't really helpful. Then have two flavors:
A "basic" version using qword steps for the bulk of the operation, and an
ERMS version for modern hardware, to be substituted in via alternatives
patching.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
We may want to consider branching over the REP STOSQ as well, if the
number of qwords turns out to be zero.
We may also want to consider using non-REP STOS{L,W,B} for the tail.
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -43,6 +43,7 @@ obj-$(CONFIG_INDIRECT_THUNK) += indirect
obj-y += ioport_emulate.o
obj-y += irq.o
obj-$(CONFIG_KEXEC) += machine_kexec.o
+obj-y += memset.o
obj-y += mm.o x86_64/mm.o
obj-$(CONFIG_HVM) += monitor.o
obj-y += mpparse.o
--- /dev/null
+++ b/xen/arch/x86/memset.S
@@ -0,0 +1,31 @@
+#include <asm/asm_defns.h>
+
+.macro memset
+ and $7, %edx
+ shr $3, %rcx
+ movzbl %sil, %esi
+ mov $0x0101010101010101, %rax
+ imul %rsi, %rax
+ mov %rdi, %rsi
+ rep stosq
+ or %edx, %ecx
+ jz 0f
+ rep stosb
+0:
+ mov %rsi, %rax
+ ret
+.endm
+
+.macro memset_erms
+ mov %esi, %eax
+ mov %rdi, %rsi
+ rep stosb
+ mov %rsi, %rax
+ ret
+.endm
+
+ENTRY(memset)
+ mov %rdx, %rcx
+ ALTERNATIVE memset, memset_erms, X86_FEATURE_ERMS
+ .type memset, @function
+ .size memset, . - memset
--- a/xen/arch/x86/string.c
+++ b/xen/arch/x86/string.c
@@ -22,19 +22,6 @@ void *(memcpy)(void *dest, const void *s
return dest;
}
-void *(memset)(void *s, int c, size_t n)
-{
- long d0, d1;
-
- asm volatile (
- "rep stosb"
- : "=&c" (d0), "=&D" (d1)
- : "a" (c), "1" (s), "0" (n)
- : "memory");
-
- return s;
-}
-
void *(memmove)(void *dest, const void *src, size_t n)
{
long d0, d1, d2;
next prev parent reply other threads:[~2021-04-27 12:54 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 12:51 [PATCH 0/7] x86: memcpy() / memset() (non-)ERMS flavors plus fallout Jan Beulich
2021-04-27 12:53 ` [PATCH 1/7] x86: correct comment about alternatives ordering Jan Beulich
2021-04-27 13:19 ` Andrew Cooper
2021-04-27 12:54 ` [PATCH 2/7] x86: introduce ioremap_wc() Jan Beulich
2021-04-27 17:13 ` Andrew Cooper
2021-04-28 9:41 ` Jan Beulich
2021-04-27 12:54 ` Jan Beulich [this message]
2021-04-27 12:54 ` [PATCH 4/7] x86: re-work memcpy() Jan Beulich
2021-04-27 12:55 ` [PATCH 5/7] video/vesa: unmap frame buffer when relinquishing console Jan Beulich
2021-04-27 12:56 ` [PATCH 6/7] video/vesa: drop "vesa-mtrr" command line option Jan Beulich
2021-04-27 13:20 ` Andrew Cooper
2021-04-27 12:56 ` [PATCH 7/7] video/vesa: adjust (not just) command line option handling Jan Beulich
2021-04-27 13:49 ` Andrew Cooper
2021-04-27 14:04 ` Jan Beulich
2021-05-27 11:47 ` Jan Beulich
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