linux-kernel - Re: uml and -regparm=3

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Date:	Thu, 10 Jan 2008 08:32:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jdike@...toit.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: uml and -regparm=3


* Miklos Szeredi <miklos@...redi.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@...e.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@...redi.hu>
Signed-off-by: Ingo Molnar <mingo@...e.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.

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