linux-kernel - Re: [uml-devel] [Patch] uml: fix a link error

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Date:	Tue, 27 Jan 2009 09:23:14 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Shane Hathaway <shane@...hawaymix.org>
Cc:	Daolong Wang <ahlongxp@...il.com>, Jeff Dike <jdike@...toit.com>,
	Rob Landley <rob@...dley.net>,
	user-mode-linux-devel@...ts.sourceforge.net,
	Andrew Morton <akpm@...ux-foundation.org>,
	Am?rico Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [uml-devel] [Patch] uml: fix a link error

On Mon, Jan 19, 2009 at 07:01:07PM -0700, Shane Hathaway wrote:
> The problem is that the name "sigprocmask" is getting renamed to
> "kernel_sigprocmask" by a compiler directive in arch/um/Makefile, then
> that name gets mangled into "sys_kernel_sigprocmask" by the
> SYSCALL_DEFINE3(sigprocmask, ...) macro in kernel/signal.c.
> 
> So, instead of the patch suggested earlier, I added the following line
> to arch/um/sys-i386/sys_call_table.S:
> 
> #define sys_sigprocmask sys_kernel_sigprocmask

Interesting...  Everything else aside, we have difference in e.g.
SYSCALL_DEFINE0 and SYSCALL_DEFINE3 behaviours: SYSCALL_DEFINE0(name)
will *not* do macro expansion in name and SYSCALL_DEFINE3(name, blah, ...)
will.

The reason is that we have name carried through extra layer of macros
in the latter case.  Argument is *NOT* a subject to expansion when it
is used with ##; however, passing it to another macro will expand it
just fine.

Regardless of the kludge with -D used by uml, I'd say that we want consistency
here; keeping the original behaviour would also be nice.

How about
#define SYSCALL_DEFINE1(name,...)    SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
etc.
with
#define SYSCALL_DEFINEx(x, name, ...)                                   \
        asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__))
?

That gives consistent behaviour in all cases and avoids the insane side
effects like this one.
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