linux kernel warnings/errors

linux kernel warnings/errors

[Randy Dunlap]

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); }))


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


3.  I don't see the problem here -- maybe it's simple (or maybe it's
related to BUILD_BUG_ON stuff):

drivers/char/ipmi/ipmi_watchdog.c:291:1: error: cannot dereference this type

referring to:

module_param_call(action, set_param_str, get_param_str, action_op, 0644);

which comes from include/linux/moduleparam.h


4.  from include/linux/swab.h:

include/linux/swab.h:51:16: warning: unreplaced symbol 'val'
include/linux/swab.h:51:16: warning: unreplaced symbol 'val'
include/linux/swab.h:51:9: warning: unreplaced symbol 'return'

referring to:

static inline __attribute_const__ __u16 __fswab16(__u16 val)
{
#ifdef __arch_swab16
	return __arch_swab16(val);
#else
	return ___constant_swab16(val);
#endif
}


5.  sparse reports (maybe correctly?):

include/linux/skbuff.h:357:41: error: invalid bitfield specifier for type restricted __be16.

on struct sk_buff, this line:

	__be16			protocol:16;


6.  sparse reports:

drivers/usb/gadget/zero.c:166:9: warning: advancing past deep designator

on

static struct usb_string strings_dev[] = {
	[STRING_MANUFACTURER_IDX].s = manufacturer,
	[STRING_PRODUCT_IDX].s = longname,
	[STRING_SERIAL_IDX].s = serial,
	{  }			/* end of list */
};

Is that an improper initializer?  The sparse warning doesn't mean much to me.



Thanks for listening, insights, etc.

---
~Randy

Re: linux kernel warnings/errors

[Josh Triplett]

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?

> 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*.

- Josh Triplett

Re: linux kernel warnings/errors

[Randy Dunlap]

[-- Attachment #1: Type: text/plain, Size: 1845 bytes --]

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

[-- Attachment #2: build_bug_on.c --]
[-- Type: text/x-csrc, Size: 713 bytes --]

/* 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[])
{
}

Re: linux kernel warnings/errors (#7)

[Randy Dunlap]

On 02/23/10 11:49, 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:

(one addition)


7.  from drivers/gpu/drm/radeon/atombios.h:

#define VESA_OEM_PRODUCT_REV			            '01.00'
#define VESA_MODE_ATTRIBUTE_MODE_SUPPORT	     0xBB	/* refer to VBE spec p.32, no TTY support */


causes sparse to say:

drivers/gpu/drm/radeon/atombios.h:4091:63: error: Bad character constant
drivers/gpu/drm/radeon/atombios.h:4092:1: error: Bad character constant


That second one is a bit confusing.  It's just a remnant of the first one...

-- 
~Randy

Re: linux kernel warnings/errors (#8)

[Randy Dunlap]

[-- Attachment #1: Type: text/plain, Size: 1427 bytes --]

On 02/23/10 11:49, 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:


8.  There are many cases of sparse "error: bad integer constant expression"
that gcc handles without a problem, when the constant expression uses a
macro or static inline function:

a.  drivers/gpu/drm/drm_drv.c:59:9: error: bad integer constant expression

static struct drm_ioctl_desc drm_ioctls[] = {
	DRM_IOCTL_DEF(DRM_IOCTL_VERSION, drm_version, 0),

b.  drivers/media/video/v4l2-ioctl.c:185:10: error: bad integer constant expression

static const char *v4l1_ioctls[] = {
	[_IOC_NR(VIDIOCGCAP)]       = "VIDIOCGCAP",
};

c.  fs/proc/array.c:154:9: error: bad integer constant expression

	BUILD_BUG_ON(1 + ilog2(TASK_STATE_MAX) != ARRAY_SIZE(task_state_array));

d.  sound/pci/hda/hda_proc.c:422:18: error: bad integer constant expression

	static char *names[] = {
		[ilog2(AC_PWRST_D0SUP)]		= "D0",
	};

e.  drivers/gpu/drm/drm_ioc32.c:1017:10: error: bad integer constant expression

drm_ioctl_compat_t *drm_compat_ioctls[] = {
	[DRM_IOCTL_NR(DRM_IOCTL_VERSION32)] = compat_drm_version,
};


I have a test case for "d." above.
(attached)

> sparse  const_sound.c 
const_sound.c:114:18: error: bad integer constant expression



-- 
~Randy

[-- Attachment #2: const_sound.c --]
[-- Type: text/x-csrc, Size: 2798 bytes --]

#include <asm-generic/ioctl.h>


static inline __attribute__((const))
int fls(unsigned int n)
{
	return 0;
}

static inline __attribute__((const))
int fls64(unsigned int n)
{
	return 63;
}

static inline __attribute__((const))
int __ilog2_u32(unsigned int n)
{
	return fls(n) - 1;
}

static inline __attribute__((const))
int __ilog2_u64(unsigned long n)
{
	return fls64(n) - 1;
}

static inline __attribute__((const))
int ____ilog2_NaN(void)
{
	return -1;
}

#define ilog2(n)				\
(						\
	__builtin_constant_p(n) ? (		\
		(n) < 1 ? ____ilog2_NaN() :	\
		(n) & (1ULL << 63) ? 63 :	\
		(n) & (1ULL << 62) ? 62 :	\
		(n) & (1ULL << 61) ? 61 :	\
		(n) & (1ULL << 60) ? 60 :	\
		(n) & (1ULL << 59) ? 59 :	\
		(n) & (1ULL << 58) ? 58 :	\
		(n) & (1ULL << 57) ? 57 :	\
		(n) & (1ULL << 56) ? 56 :	\
		(n) & (1ULL << 55) ? 55 :	\
		(n) & (1ULL << 54) ? 54 :	\
		(n) & (1ULL << 53) ? 53 :	\
		(n) & (1ULL << 52) ? 52 :	\
		(n) & (1ULL << 51) ? 51 :	\
		(n) & (1ULL << 50) ? 50 :	\
		(n) & (1ULL << 49) ? 49 :	\
		(n) & (1ULL << 48) ? 48 :	\
		(n) & (1ULL << 47) ? 47 :	\
		(n) & (1ULL << 46) ? 46 :	\
		(n) & (1ULL << 45) ? 45 :	\
		(n) & (1ULL << 44) ? 44 :	\
		(n) & (1ULL << 43) ? 43 :	\
		(n) & (1ULL << 42) ? 42 :	\
		(n) & (1ULL << 41) ? 41 :	\
		(n) & (1ULL << 40) ? 40 :	\
		(n) & (1ULL << 39) ? 39 :	\
		(n) & (1ULL << 38) ? 38 :	\
		(n) & (1ULL << 37) ? 37 :	\
		(n) & (1ULL << 36) ? 36 :	\
		(n) & (1ULL << 35) ? 35 :	\
		(n) & (1ULL << 34) ? 34 :	\
		(n) & (1ULL << 33) ? 33 :	\
		(n) & (1ULL << 32) ? 32 :	\
		(n) & (1ULL << 31) ? 31 :	\
		(n) & (1ULL << 30) ? 30 :	\
		(n) & (1ULL << 29) ? 29 :	\
		(n) & (1ULL << 28) ? 28 :	\
		(n) & (1ULL << 27) ? 27 :	\
		(n) & (1ULL << 26) ? 26 :	\
		(n) & (1ULL << 25) ? 25 :	\
		(n) & (1ULL << 24) ? 24 :	\
		(n) & (1ULL << 23) ? 23 :	\
		(n) & (1ULL << 22) ? 22 :	\
		(n) & (1ULL << 21) ? 21 :	\
		(n) & (1ULL << 20) ? 20 :	\
		(n) & (1ULL << 19) ? 19 :	\
		(n) & (1ULL << 18) ? 18 :	\
		(n) & (1ULL << 17) ? 17 :	\
		(n) & (1ULL << 16) ? 16 :	\
		(n) & (1ULL << 15) ? 15 :	\
		(n) & (1ULL << 14) ? 14 :	\
		(n) & (1ULL << 13) ? 13 :	\
		(n) & (1ULL << 12) ? 12 :	\
		(n) & (1ULL << 11) ? 11 :	\
		(n) & (1ULL << 10) ? 10 :	\
		(n) & (1ULL <<  9) ?  9 :	\
		(n) & (1ULL <<  8) ?  8 :	\
		(n) & (1ULL <<  7) ?  7 :	\
		(n) & (1ULL <<  6) ?  6 :	\
		(n) & (1ULL <<  5) ?  5 :	\
		(n) & (1ULL <<  4) ?  4 :	\
		(n) & (1ULL <<  3) ?  3 :	\
		(n) & (1ULL <<  2) ?  2 :	\
		(n) & (1ULL <<  1) ?  1 :	\
		(n) & (1ULL <<  0) ?  0 :	\
		____ilog2_NaN()			\
				   ) :		\
	(sizeof(n) <= 4) ?			\
	__ilog2_u32(n) :			\
	__ilog2_u64(n)				\
 )

// d.  sound/pci/hda/hda_proc.c:422:18: error: bad integer constant expression

#define AC_PWRST_D0SUP			(1<<0)

	static char *names[] = {
		[ilog2(AC_PWRST_D0SUP)]		= "D0",
	};


int main(int argc, char *argv[])
{
}