> Date: Sat, 24 Dec 2016 00:08:35 +0100 (CET)
> From: Mark Kettenis <[email protected]>
>
> We already do this on some architectures, but not on amd64 for
> example. The main reason is that this disables memcpy() optimizations
> that have a measurable impact on the network stack performance.
>
> We can get those optimizations back by doing:
>
> #define memcpy(d, s, n) __builtin_memcpy((d), (s), (n))
>
> I verified that gcc still does proper bounds checking on
> __builtin_memcpy(), so we don't lose that.
>
> The nice thing about this solution is that we can choose explicitly
> which optimizations we want. And as you can see the kernel makefile
> gets simpler ;).
>
> Of course the real reason why I'm looking into this is that clang
> makes it really hard to build kernels without -ffreestanding.
>
> The diff below implements this strategy, and enabled the optimizations
> for memcpy() and memset(). We can add others if we think there is a
> benefit. I've tested the diff on amd64. We may need to put an #undef
> memcpy somewhere for platforms that use the generic C code for memcpy.
>
> Thoughts?
So those #undefs are necessary. New diff below. Tested on armv7,
hppa and sparc64 now as well.
Index: sys/systm.h
===================================================================
RCS file: /cvs/src/sys/sys/systm.h,v
retrieving revision 1.119
diff -u -p -r1.119 systm.h
--- sys/systm.h 24 Sep 2016 18:35:52 -0000 1.119
+++ sys/systm.h 24 Dec 2016 16:05:48 -0000
@@ -306,6 +306,9 @@ extern int (*mountroot)(void);
#include <lib/libkern/libkern.h>
+#define memcpy(d, s, n) __builtin_memcpy((d), (s), (n))
+#define memset(b, c, n) __builtin_memset((b), (c), (n))
+
#if defined(DDB) || defined(KGDB)
/* debugger entry points */
void Debugger(void); /* in DDB only */
Index: lib/libkern/memcpy.c
===================================================================
RCS file: /cvs/src/sys/lib/libkern/memcpy.c,v
retrieving revision 1.3
diff -u -p -r1.3 memcpy.c
--- lib/libkern/memcpy.c 12 Jun 2013 16:44:22 -0000 1.3
+++ lib/libkern/memcpy.c 24 Dec 2016 16:05:48 -0000
@@ -32,6 +32,8 @@
#include <sys/types.h>
#include <sys/systm.h>
+#undef memcpy
+
/*
* This is designed to be small, not fast.
*/
Index: lib/libkern/memset.c
===================================================================
RCS file: /cvs/src/sys/lib/libkern/memset.c,v
retrieving revision 1.7
diff -u -p -r1.7 memset.c
--- lib/libkern/memset.c 10 Jun 2014 04:16:57 -0000 1.7
+++ lib/libkern/memset.c 24 Dec 2016 16:05:48 -0000
@@ -39,6 +39,8 @@
#include <sys/systm.h>
#include <lib/libkern/libkern.h>
+#undef memset
+
#define wsize sizeof(u_int)
#define wmask (wsize - 1)
Index: arch/amd64/conf/Makefile.amd64
===================================================================
RCS file: /cvs/src/sys/arch/amd64/conf/Makefile.amd64,v
retrieving revision 1.74
diff -u -p -r1.74 Makefile.amd64
--- arch/amd64/conf/Makefile.amd64 29 Nov 2016 09:08:34 -0000 1.74
+++ arch/amd64/conf/Makefile.amd64 24 Dec 2016 16:05:49 -0000
@@ -29,9 +29,7 @@ CWARNFLAGS= -Werror -Wall -Wimplicit-fun
CMACHFLAGS= -mcmodel=kernel -mno-red-zone -mno-sse2 -mno-sse -mno-3dnow \
-mno-mmx -msoft-float -fno-omit-frame-pointer
-CMACHFLAGS+= -fno-builtin-printf -fno-builtin-snprintf \
- -fno-builtin-vsnprintf -fno-builtin-log \
- -fno-builtin-log2 -fno-builtin-malloc ${NOPIE_FLAGS}
+CMACHFLAGS+= -ffreestanding ${NOPIE_FLAGS}
.if ${IDENT:M-DNO_PROPOLICE}
CMACHFLAGS+= -fno-stack-protector
.endif
