2006-08-28 09:20:26

by Gerd Hoffmann

[permalink] [raw]

Subject: [patch] fix up smp alternatives on x86-64

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Subject: fix up smp alternatives on x86-64

Don't use alternative_smp() in for __raw_spin_lock. gcc
sometimes generates rip-relative addressing, so we can't
simply copy the instruction to another place.

Replace some leftover "lock;" with LOCK_PREFIX.

Fillup space with 0x90 (nop) instead of 0x42, so
"objdump -d -j .smp_altinstr_replacement vmlinux" gives more
readable results.

Signed-off-by: Gerd Hoffmann <[email protected]>
Index: linux-2.6.17/include/asm-i386/alternative.h
===================================================================
--- linux-2.6.17.orig/include/asm-i386/alternative.h 2006-08-28 10:21:18.000000000 +0200
+++ linux-2.6.17/include/asm-i386/alternative.h 2006-08-28 10:22:59.000000000 +0200
@@ -122,7 +122,7 @@ static inline void alternatives_smp_swit
".previous\n" \
".section .smp_altinstr_replacement,\"awx\"\n" \
"663:\n\t" upinstr "\n" /* replacement */ \
- "664:\n\t.fill 662b-661b,1,0x42\n" /* space for original */ \
+ "664:\n\t.fill 662b-661b,1,0x90\n" /* space for original */ \
".previous" : args)

#define LOCK_PREFIX \
Index: linux-2.6.17/include/asm-x86_64/alternative.h
===================================================================
--- linux-2.6.17.orig/include/asm-x86_64/alternative.h 2006-08-28 10:21:21.000000000 +0200
+++ linux-2.6.17/include/asm-x86_64/alternative.h 2006-08-28 10:23:13.000000000 +0200
@@ -136,7 +136,7 @@ static inline void alternatives_smp_swit
".previous\n" \
".section .smp_altinstr_replacement,\"awx\"\n" \
"663:\n\t" upinstr "\n" /* replacement */ \
- "664:\n\t.fill 662b-661b,1,0x42\n" /* space for original */ \
+ "664:\n\t.fill 662b-661b,1,0x90\n" /* space for original */ \
".previous" : args)

#define LOCK_PREFIX \
Index: linux-2.6.17/include/asm-x86_64/spinlock.h
===================================================================
--- linux-2.6.17.orig/include/asm-x86_64/spinlock.h 2006-08-28 10:21:21.000000000 +0200
+++ linux-2.6.17/include/asm-x86_64/spinlock.h 2006-08-28 11:07:14.000000000 +0200
@@ -21,7 +21,7 @@

#define __raw_spin_lock_string \
"\n1:\t" \
- "lock ; decl %0\n\t" \
+ LOCK_PREFIX "decl %0\n\t" \
"js 2f\n" \
LOCK_SECTION_START("") \
"2:\t" \
@@ -40,10 +40,18 @@

static inline void __raw_spin_lock(raw_spinlock_t *lock)
{
+#if 0
+ /* gcc sometimes uses %(rip) addressing, so we can't
+ * simply move around instructions ... */
alternative_smp(
__raw_spin_lock_string,
__raw_spin_lock_string_up,
"=m" (lock->slock) : : "memory");
+#else
+ __asm__ __volatile__(
+ __raw_spin_lock_string
+ : "=m" (lock->slock) : : "memory");
+#endif
}

#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
@@ -125,12 +133,12 @@ static inline int __raw_write_trylock(ra

static inline void __raw_read_unlock(raw_rwlock_t *rw)
{
- asm volatile("lock ; incl %0" :"=m" (rw->lock) : : "memory");
+ asm volatile(LOCK_PREFIX "incl %0" :"=m" (rw->lock) : : "memory");
}

static inline void __raw_write_unlock(raw_rwlock_t *rw)
{
- asm volatile("lock ; addl $" RW_LOCK_BIAS_STR ",%0"
+ asm volatile(LOCK_PREFIX "lock ; addl $" RW_LOCK_BIAS_STR ",%0"
: "=m" (rw->lock) : : "memory");
}

---

Attachments:

smpalt-fixup (3.17 kB)

2006-08-28 09:22:45

by Andi Kleen

[permalink] [raw]

Subject: Re: [patch] fix up smp alternatives on x86-64

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On Monday 28 August 2006 11:20, Gerd Hoffmann wrote:
> Don't use alternative_smp() in for __raw_spin_lock. gcc
> sometimes generates rip-relative addressing, so we can't
> simply copy the instruction to another place.
>
> Replace some leftover "lock;" with LOCK_PREFIX.
>
> Fillup space with 0x90 (nop) instead of 0x42, so
> "objdump -d -j .smp_altinstr_replacement vmlinux" gives more
> readable results.

I already fixed it myself.

ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/remove-alternative-smp
ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/i386-remove-alternative-smp

And all the left over lock prefixes are also gone in that tree.

-Andi