On Sun, Oct 07, 2012 at 07:49:25AM -0500, Ed Cashin wrote:
> On Oct 6, 2012, at 10:39 PM, Josh Triplett wrote:
>
> > On Sat, Oct 06, 2012 at 08:56:57PM -0500, Ed Cashin wrote:
> ...
> >> OK. From the sparse man page section on context, along with
> >> include/linux/compiler.h, it sounds like the way to do exactly that
> >> would be something unusual:
> >>
> >> int demofn(void) __attribute__((context(&lk,1,1)))
> >>
> >> ... but using that in demo.c causes sparse to warn me that it's
> >> ignoring that attribute, so I doubt that can be what you mean.
> >
> > I did mean precisely that; I don't know why Sparse complains about that
> > syntax.
>
> Maybe there's a header I need. Searching with cscope and ctags for definitions of "context" doesn't seem to be the right kind of searching.
>
> The complaint looks like:
>
> CC [M] drivers/block/aoe/demo.o
> drivers/block/aoe/demo.c:9: warning: `context' attribute directive ignored
> drivers/block/aoe/demo.c:9: error: expected `,' or `;' before `{' token
> make[1]: *** [drivers/block/aoe/demo.o] Error 1
> make: *** [drivers/block/aoe/aoe.ko] Error 2
Oh, that complaint doesn't come from Sparse; that comes from GCC, since
GCC doesn't understand the context attribute. Look at
include/linux/compiler.h; it has wrapper macros for the various Sparse
attributes, and defines them to nothing when not compiling with Sparse.
If you want to use the context attribute to denote a lock held through a
function, you need a patch like this:
>From 0b862fc1a131a874d157420e9443f16a714596ef Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Date: Sun, 7 Oct 2012 12:41:13 -0700
Subject: [PATCH] linux/compiler.h: Add __must_hold macro for functions called with a lock held
linux/compiler.h has macros to denote functions that acquire or release
locks, but not to denote functions called with a lock held that return
with the lock still held. Add a __must_hold macro to cover this case.
Signed-off-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
---
include/linux/compiler.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index f430e41..b121554 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -10,6 +10,7 @@
# define __force __attribute__((force))
# define __nocast __attribute__((nocast))
# define __iomem __attribute__((noderef, address_space(2)))
+# define __must_hold(x) __attribute__((context(x,1,1)))
# define __acquires(x) __attribute__((context(x,0,1)))
# define __releases(x) __attribute__((context(x,1,0)))
# define __acquire(x) __context__(x,1)
@@ -33,6 +34,7 @@ extern void __chk_io_ptr(const volatile void __iomem *);
# define __chk_user_ptr(x) (void)0
# define __chk_io_ptr(x) (void)0
# define __builtin_warning(x, y...) (1)
+# define __must_hold(x)
# define __acquires(x)
# define __releases(x)
# define __acquire(x) (void)0
--
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