linux-kernel - How to trace compat syscalls? [Was Re: [PATCH] MIPS: use 32-bit wrapper for compat_sys

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Date:	Fri, 19 Aug 2011 11:49:50 +0800
From:	Yong Zhang <yong.zhang@...driver.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	David Daney <david.daney@...ium.com>, <linux-mips@...ux-mips.org>,
	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	Yong Zhang <yong.zhang0@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: How to trace compat syscalls? [Was Re: [PATCH] MIPS: use 32-bit
 wrapper for compat_sys_futex]

Cc'ing more people.

On Thu, Aug 18, 2011 at 09:19:11PM +0100, Ralf Baechle wrote:
> > But really I think this patch fixes things at the wrong level.  Each
> > architecture potentially needs a similar patch.  What would happen if
> > we did something like:
> 
> > +++ b/kernel/futex_compat.c
> > @@ -180,9 +180,9 @@ err_unlock:
> >  	return ret;
> >  }
> > 
> > -asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
> > -		struct compat_timespec __user *utime, u32 __user *uaddr2,
> > -		u32 val3)
> > +SYSCALL_DEFINE6(compat_sys_futex, u32 __user *, uaddr, int , op, u32, val,
> > +		struct compat_timespec __user *, utime, u32 __user *, uaddr2,
> > +		u32, val3)
> >  {
> >  	struct timespec ts;
> >  	ktime_t t, *tp = NULL;
> > 
> > Obviously the function name is wrong, but a varient of
> > SYSCALL_DEFINE*() could be created so the proper function names are
> > produced.
> 
> Right now none of the the generic compat_ functions is wrapped in
> SYSCALL_DEFINE* because for some architectures a further wrapper function
> is needed.  It seems some architectures call compat_ calls directly
> without SYSCALL_DEFINE* which with CONFIG_FTRACE_SYSCALLS is a bug ...

Just checked some archs which have HAVE_SYSCALL_TRACEPOINTS=y and could
call compat_* syscalls when run 32bit process on 64bit kernel, I don't
find any special code against FTRACE_SYSCALLS. So that means we could
not trace compat syscalls even if we want to(Am I missing something?).
So I think if we want to trace it, the easy way is just like what we have
done on normal syscalls, IOW, we could SYSCALL_DEFINE all of the compat
syscalls.

Thought?

BTW, I have make a trival patch to introduce COMPAT_SYSCALL_DEFINE, it's just
for calling of inspiration(no test no build, and I leave SYSCALL_METADATA
etc untouched.)

Thanks,
Yong

---
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 8c03b98..e79027f 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -221,26 +221,38 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 		__SC_STR_ADECL##x(__VA_ARGS__)			\
 	};							\
 	SYSCALL_METADATA(sname, x);				\
-	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
+	__SYSCALL_DEFINEx(, x, sname, __VA_ARGS__)
+
+#define COMPAT_SYSCALL_DEFINEx(x, sname, ...)			\
+	static const char *types_compat_##sname[] = {		\
+		__SC_STR_TDECL##x(__VA_ARGS__)			\
+	};							\
+	static const char *args_compat_##sname[] = {		\
+		__SC_STR_ADECL##x(__VA_ARGS__)			\
+	};							\
+	SYSCALL_METADATA(compat, sname, x);			\
+	__SYSCALL_DEFINEx(cmopat_, x, sname, __VA_ARGS__)
 #else
 #define SYSCALL_DEFINEx(x, sname, ...)				\
-	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
+	__SYSCALL_DEFINEx(, x, sname, __VA_ARGS__)
+#define COMPAT_SYSCALL_DEFINEx(x, sname, ...)			\
+	__SYSCALL_DEFINEx(compat_, x, sname, __VA_ARGS__)
 #endif
 
 #ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
 
-#define SYSCALL_DEFINE(name) static inline long SYSC_##name
+#define SYSCALL_DEFINE(compat, name) static inline long compat##SYSC_##name
 
-#define __SYSCALL_DEFINEx(x, name, ...)					\
-	asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__));		\
-	static inline long SYSC##name(__SC_DECL##x(__VA_ARGS__));	\
-	asmlinkage long SyS##name(__SC_LONG##x(__VA_ARGS__))		\
+#define __SYSCALL_DEFINEx(compat, x, name, ...)				\
+	asmlinkage long compat##sys##name(__SC_DECL##x(__VA_ARGS__));	\
+	static inline long compat##SYSC##name(__SC_DECL##x(__VA_ARGS__));\
+	asmlinkage long compat##SyS##name(__SC_LONG##x(__VA_ARGS__))	\
 	{								\
 		__SC_TEST##x(__VA_ARGS__);				\
-		return (long) SYSC##name(__SC_CAST##x(__VA_ARGS__));	\
+		return (long) compat##SYSC##name(__SC_CAST##x(__VA_ARGS__));\
 	}								\
-	SYSCALL_ALIAS(sys##name, SyS##name);				\
-	static inline long SYSC##name(__SC_DECL##x(__VA_ARGS__))
+	SYSCALL_ALIAS(compat##sys##name, compat##SyS##name);		\
+	static inline long compat##SYSC##name(__SC_DECL##x(__VA_ARGS__))
 
 #else /* CONFIG_HAVE_SYSCALL_WRAPPERS */
 
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