Re: uml and -regparm=3

Ingo Molnar
2008-01-10T07:32:54Z

* 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)]

Ingo

------------>
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.

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/asm-x86/linkage.h | 5 +++++
include/asm-x86/rwsem.h | 12 ++++++++----
include/asm-x86/semaphore_32.h | 8 ++++----
3 files changed, 17 insertions(+), 8 deletions(-)

Index: linux-x86.q/include/asm-x86/linkage.h
===================================================================
--- linux-x86.q.orig/include/asm-x86/linkage.h
+++ linux-x86.q/include/asm-x86/linkage.h
@@ -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-x86.q/include/asm-x86/rwsem.h
===================================================================
--- linux-x86.q.orig/include/asm-x86/rwsem.h
+++ linux-x86.q/include/asm-x86/rwsem.h
@@ -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-x86.q/include/asm-x86/semaphore_32.h
===================================================================
--- linux-x86.q.orig/include/asm-x86/semaphore_32.h
+++ linux-x86.q/include/asm-x86/semaphore_32.h
@@ -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.