Re: uml and -regparm=3

Miklos Szeredi
2008-01-10T09:06:37Z

> * Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> > FASTCALL is defined empty in -mm, but UML is not compiled with
> > -mregparm=3 and so this breaks things (I noticed problems with
> > rwsem_down_write_failed).
> >
> > Tried recompiling UML with -mregparm=3, but that resulted in a strange
> > failure immediately after startup:
> >
> > |^[%Gï¿½^[%@: Invalid argument
> >
> > What's up?
>
> Miklos, could you try the fix below?
>
> In general most FASTCALL/fastcall uses are bogus, except for code where
> a function that takes parameters is implemented in assembly with a
> regparm calling convention. The fix is to introduce the "asmregparm"
> attribute to mark such function prototypes with regparm(3). This is the
> opposite of asmlinkage. [asmlinkage forced regparm(0)]

Thanks. Patch works, but needed to add asmregparm to the definitions
as well, plus added default define into <linux/linkage.h> (updated
patch below).

Miklos
----

Subject: x86: fix UML calling convention
From: Ingo Molnar <mingo@elte.hu>

introduce the "asmregparm" calling convention: for functions
implemented in assembly with a fixed regparm input parameters
calling convention.

mark the semaphore and rwsem slowpath functions with that.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/include/asm-x86/linkage.h
===================================================================
--- linux.orig/include/asm-x86/linkage.h 2008-01-09 21:16:29.000000000 +0100
+++ linux/include/asm-x86/linkage.h 2008-01-10 09:38:17.000000000 +0100
@@ -9,6 +9,11 @@
#ifdef CONFIG_X86_32
#define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
#define prevent_tail_call(ret) __asm__ ("" : "=r" (ret) : "0" (ret))
+/*
+ * For 32-bit UML - mark functions implemented in assembly that use
+ * regparm input parameters:
+ */
+#define asmregparm __attribute__((regparm(3)))
#endif

#ifdef CONFIG_X86_ALIGNMENT_16
Index: linux/include/asm-x86/rwsem.h
===================================================================
--- linux.orig/include/asm-x86/rwsem.h 2008-01-09 21:16:29.000000000 +0100
+++ linux/include/asm-x86/rwsem.h 2008-01-10 09:55:07.000000000 +0100
@@ -44,10 +44,14 @@

struct rwsem_waiter;

-extern struct rw_semaphore *FASTCALL(rwsem_down_read_failed(struct rw_semaphore *sem));
-extern struct rw_semaphore *FASTCALL(rwsem_down_write_failed(struct rw_semaphore *sem));
-extern struct rw_semaphore *FASTCALL(rwsem_wake(struct rw_semaphore *));
-extern struct rw_semaphore *FASTCALL(rwsem_downgrade_wake(struct rw_semaphore *sem));
+extern asmregparm struct rw_semaphore *
+ rwsem_down_read_failed(struct rw_semaphore *sem);
+extern asmregparm struct rw_semaphore *
+ rwsem_down_write_failed(struct rw_semaphore *sem);
+extern asmregparm struct rw_semaphore *
+ rwsem_wake(struct rw_semaphore *);
+extern asmregparm struct rw_semaphore *
+ rwsem_downgrade_wake(struct rw_semaphore *sem);

/*
* the semaphore definition
Index: linux/include/asm-x86/semaphore_32.h
===================================================================
--- linux.orig/include/asm-x86/semaphore_32.h 2008-01-09 21:16:29.000000000 +0100
+++ linux/include/asm-x86/semaphore_32.h 2008-01-10 09:38:17.000000000 +0100
@@ -83,10 +83,10 @@ static inline void init_MUTEX_LOCKED (st
sema_init(sem, 0);
}

-void __down_failed(void /* special register calling convention */);
-int __down_failed_interruptible(void /* params in registers */);
-int __down_failed_trylock(void /* params in registers */);
-void __up_wakeup(void /* special register calling convention */);
+extern asmregparm void __down_failed(atomic_t *count_ptr);
+extern asmregparm int __down_failed_interruptible(atomic_t *count_ptr);
+extern asmregparm int __down_failed_trylock(atomic_t *count_ptr);
+extern asmregparm void __up_wakeup(atomic_t *count_ptr);

/*
* This is ugly, but we want the default case to fall through.
Index: linux/lib/rwsem.c
===================================================================
--- linux.orig/lib/rwsem.c 2008-01-09 21:16:30.000000000 +0100
+++ linux/lib/rwsem.c 2008-01-10 09:55:55.000000000 +0100
@@ -187,7 +187,7 @@ rwsem_down_failed_common(struct rw_semap
/*
* wait for the read lock to be granted
*/
-struct rw_semaphore __sched *
+asmregparm struct rw_semaphore __sched *
rwsem_down_read_failed(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
@@ -201,7 +201,7 @@ rwsem_down_read_failed(struct rw_semapho
/*
* wait for the write lock to be granted
*/
-struct rw_semaphore __sched *
+asmregparm struct rw_semaphore __sched *
rwsem_down_write_failed(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
@@ -216,7 +216,7 @@ rwsem_down_write_failed(struct rw_semaph
* handle waking up a waiter on the semaphore
* - up_read/up_write has decremented the active part of count if we come here
*/
-struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
+asmregparm struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
{
unsigned long flags;

@@ -236,7 +236,7 @@ struct rw_semaphore *rwsem_wake(struct r
* - caller incremented waiting part of count and discovered it still negative
* - just wake up any readers at the front of the queue
*/
-struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
+asmregparm struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
{
unsigned long flags;

Index: linux/include/linux/linkage.h
===================================================================
--- linux.orig/include/linux/linkage.h 2008-01-09 21:16:04.000000000 +0100
+++ linux/include/linux/linkage.h 2008-01-10 10:01:52.000000000 +0100
@@ -13,6 +13,10 @@
#define asmlinkage CPP_ASMLINKAGE
#endif

+#ifndef asmregparm
+#define asmregparm
+#endif
+
#ifndef prevent_tail_call
# define prevent_tail_call(ret) do { } while (0)
#endif