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SubjectRe: Semaphore assembly-code bug


Here's a totally untested patch to make the semaphores use "fastcall"
instead of "asmlinkage", and thus pass the argument in %eax instead of on
the stack. Does it work? I have no idea. If it does, it should fix the
particular bug that started this thread..

Linus

---
===== arch/i386/kernel/semaphore.c 1.10 vs edited =====
--- 1.10/arch/i386/kernel/semaphore.c 2004-04-12 10:53:59 -07:00
+++ edited/arch/i386/kernel/semaphore.c 2004-10-29 12:19:22 -07:00
@@ -49,12 +49,12 @@
* we cannot lose wakeup events.
*/

-asmlinkage void __up(struct semaphore *sem)
+fastcall void __up(struct semaphore *sem)
{
wake_up(&sem->wait);
}

-asmlinkage void __sched __down(struct semaphore * sem)
+fastcall void __sched __down(struct semaphore * sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
@@ -91,7 +91,7 @@
tsk->state = TASK_RUNNING;
}

-asmlinkage int __sched __down_interruptible(struct semaphore * sem)
+fastcall int __sched __down_interruptible(struct semaphore * sem)
{
int retval = 0;
struct task_struct *tsk = current;
@@ -154,7 +154,7 @@
* single "cmpxchg" without failure cases,
* but then it wouldn't work on a 386.
*/
-asmlinkage int __down_trylock(struct semaphore * sem)
+fastcall int __down_trylock(struct semaphore * sem)
{
int sleepers;
unsigned long flags;
@@ -183,9 +183,9 @@
* need to convert that sequence back into the C sequence when
* there is contention on the semaphore.
*
- * %ecx contains the semaphore pointer on entry. Save the C-clobbered
- * registers (%eax, %edx and %ecx) except %eax when used as a return
- * value..
+ * %eax contains the semaphore pointer on entry. Save the C-clobbered
+ * registers (%eax, %edx and %ecx) except %eax whish is either a return
+ * value or just clobbered..
*/
asm(
".section .sched.text\n"
@@ -196,13 +196,11 @@
"pushl %ebp\n\t"
"movl %esp,%ebp\n\t"
#endif
- "pushl %eax\n\t"
"pushl %edx\n\t"
"pushl %ecx\n\t"
"call __down\n\t"
"popl %ecx\n\t"
"popl %edx\n\t"
- "popl %eax\n\t"
#if defined(CONFIG_FRAME_POINTER)
"movl %ebp,%esp\n\t"
"popl %ebp\n\t"
@@ -257,13 +255,11 @@
".align 4\n"
".globl __up_wakeup\n"
"__up_wakeup:\n\t"
- "pushl %eax\n\t"
"pushl %edx\n\t"
"pushl %ecx\n\t"
"call __up\n\t"
"popl %ecx\n\t"
"popl %edx\n\t"
- "popl %eax\n\t"
"ret"
);

===== include/asm-i386/linkage.h 1.4 vs edited =====
--- 1.4/include/asm-i386/linkage.h 2004-10-16 18:24:37 -07:00
+++ edited/include/asm-i386/linkage.h 2004-10-29 11:32:18 -07:00
@@ -1,7 +1,7 @@
#ifndef __ASM_LINKAGE_H
#define __ASM_LINKAGE_H

-#define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
+#define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(3)))
#define FASTCALL(x) x __attribute__((regparm(3)))
#define fastcall __attribute__((regparm(3)))

===== include/asm-i386/semaphore.h 1.9 vs edited =====
--- 1.9/include/asm-i386/semaphore.h 2004-08-27 00:02:38 -07:00
+++ edited/include/asm-i386/semaphore.h 2004-10-29 12:06:48 -07:00
@@ -87,15 +87,15 @@
sema_init(sem, 0);
}

-asmlinkage void __down_failed(void /* special register calling convention */);
-asmlinkage int __down_failed_interruptible(void /* params in registers */);
-asmlinkage int __down_failed_trylock(void /* params in registers */);
-asmlinkage void __up_wakeup(void /* special register calling convention */);
-
-asmlinkage void __down(struct semaphore * sem);
-asmlinkage int __down_interruptible(struct semaphore * sem);
-asmlinkage int __down_trylock(struct semaphore * sem);
-asmlinkage void __up(struct semaphore * sem);
+fastcall void __down_failed(void /* special register calling convention */);
+fastcall int __down_failed_interruptible(void /* params in registers */);
+fastcall int __down_failed_trylock(void /* params in registers */);
+fastcall void __up_wakeup(void /* special register calling convention */);
+
+fastcall void __down(struct semaphore * sem);
+fastcall int __down_interruptible(struct semaphore * sem);
+fastcall int __down_trylock(struct semaphore * sem);
+fastcall void __up(struct semaphore * sem);

/*
* This is ugly, but we want the default case to fall through.
@@ -111,12 +111,13 @@
"js 2f\n"
"1:\n"
LOCK_SECTION_START("")
- "2:\tcall __down_failed\n\t"
+ "2:\tlea %0,%%eax\n\t"
+ "call __down_failed\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=m" (sem->count)
- :"c" (sem)
- :"memory");
+ :
+ :"memory","ax");
}

/*
@@ -135,11 +136,12 @@
"xorl %0,%0\n"
"1:\n"
LOCK_SECTION_START("")
- "2:\tcall __down_failed_interruptible\n\t"
+ "2:\tlea %1,%%eax\n\t"
+ "call __down_failed_interruptible\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=a" (result), "=m" (sem->count)
- :"c" (sem)
+ :
:"memory");
return result;
}
@@ -159,11 +161,12 @@
"xorl %0,%0\n"
"1:\n"
LOCK_SECTION_START("")
- "2:\tcall __down_failed_trylock\n\t"
+ "2:\tlea %1,%%eax\n\t"
+ "call __down_failed_trylock\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=a" (result), "=m" (sem->count)
- :"c" (sem)
+ :
:"memory");
return result;
}
@@ -182,13 +185,14 @@
"jle 2f\n"
"1:\n"
LOCK_SECTION_START("")
- "2:\tcall __up_wakeup\n\t"
+ "2:\tlea %0,%%eax\n\t"
+ "call __up_wakeup\n\t"
"jmp 1b\n"
LOCK_SECTION_END
".subsection 0\n"
:"=m" (sem->count)
- :"c" (sem)
- :"memory");
+ :
+ :"memory","ax");
}

#endif
===== include/linux/spinlock.h 1.32 vs edited =====
--- 1.32/include/linux/spinlock.h 2004-10-24 16:24:20 -07:00
+++ edited/include/linux/spinlock.h 2004-10-29 12:08:14 -07:00
@@ -27,7 +27,7 @@
extra \
".ifndef " LOCK_SECTION_NAME "\n\t" \
LOCK_SECTION_NAME ":\n\t" \
- ".endif\n\t"
+ ".endif\n"

#define LOCK_SECTION_END \
".previous\n\t"
-
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