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List: linux-sparse
Subject: Re: linux kernel warnings/errors
From: Randy Dunlap <rdunlap () xenotime ! net>
Date: 2010-02-23 22:20:49
Message-ID: 4B8454C1.6010402 () xenotime ! net
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On 02/23/10 12:59, Josh Triplett wrote:
> On Tue, Feb 23, 2010 at 11:49:06AM -0800, Randy Dunlap wrote:
>> Hi,
>>
>> You probably know that sparse produces a ton of errors & warnings when
>> run on the Linux kernel tree (a little over 1 MB in my latest 'make C=1'
>> on x86_64 arch.).
>>
>> I'm wondering if all of these are valid.
>>
>> Examples:
>>
>>
>> 1. Use of the BUILD_BUG_ON() macro causes this error from sparse:
>>
>> arch/x86/kernel/paravirt.c:101:9: error: invalid bitfield width, -1.
>>
>> include/linux/kernel.h:
>>
>> /* Force a compilation error if condition is true */
>> #define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition))
>>
>> /* Force a compilation error if condition is true, but also produce a
>> result (of value 0 and type size_t), so the expression can be used
>> e.g. in a structure initializer (or where-ever else comma expressions
>> aren't permitted). */
>> #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
>
> In theory that should only happen if the BUILD_BUG_ON_ZERO actually
> triggers, and thus sparse fails to build just as GCC would. If sparse
> has this problem and GCC doesn't, could you please provide a minimal
> test case?
Sure, attached.
>> 2. drivers/block/drbd/drbd_int.h uses __protected_by(var);
>> this seems to be unknown to sparse.
>>
>> #ifdef __CHECKER__
>> # define __protected_by(x) __attribute__((require_context(x,1,999,"rdwr")))
>>
>> sparse says many times:
>>
>> drivers/block/drbd/drbd_int.h:887:39: error: attribute 'require_context': unknown attribute
>
> That looks broken. A few patches went around for new Sparse
> context-tracking features, one of which got reverted before the 0.4.2
> release, but I don't think any of them would have allowed *that*.
Yeah, I recall seeing some of the context patches.
Thanks.
--
~Randy
["build_bug_on.c" (text/x-csrc)]
/* Force a compilation error if condition is true */
#define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition))
/* Force a compilation error if condition is true, but also produce a
result (of value 0 and type size_t), so the expression can be used
e.g. in a structure initializer (or where-ever else comma expressions
aren't permitted). */
#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
struct branch {
unsigned char opcode;
int delta;
} __attribute__((packed));
unsigned paravirt_patch_call(void *insnbuf)
{
struct branch *b = insnbuf;
b->opcode = 0xe8; /* call */
b->delta = 0x1234;
BUILD_BUG_ON(sizeof(*b) != 5);
return 5;
}
int main(int argc, char *argv[])
{
}
--
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