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Fix _IOC_TYPECHECK sparse error

PATCH In review Hans Verkuil 2 participants 3 messages May 9, 2014 – May 12, 2014

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Media (V4L/DVB) Generic include/asm header files
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Hans Verkuil

author
#0 lore raw

PATCH 1/1 Fix _IOC_TYPECHECK sparse error

Andrew, can you merge this for 3.15 or 3.16 (you decide)? While it fixes a sparse error for the media subsystem, it is not really appropriate to go through our media tree.

Thanks,

Hans

When running sparse over drivers/media/v4l2-core/v4l2-ioctl.c I get these errors:

drivers/media/v4l2-core/v4l2-ioctl.c:2043:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2044:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2045:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2046:9: error: bad integer constant expression

etc.

The root cause of that turns out to be in include/asm-generic/ioctl.h:

#include <uapi/asm-generic/ioctl.h>

/* provoke compile error for invalid uses of size argument */ extern unsigned int __invalid_size_argument_for_IOC;

#define _IOC_TYPECHECK(t) \
        ((sizeof(t) == sizeof(t[1]) && \
          sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
          sizeof(t) : __invalid_size_argument_for_IOC)

If it is defined as this (as is already done if __KERNEL__ is not defined):

#define _IOC_TYPECHECK(t) (sizeof(t))

then all is well with the world.

This patch allows sparse to work correctly.

Signed-off-by Hans Verkuil <[email protected]>
Reviewed-by Josh Triplett <[email protected]>
---
 include/asm-generic/ioctl.h | 5 +++++
 1 file changed, 5 insertions(+)
include/asm-generic/ioctl.h +5 -0
index d17295b..297fb0d 100644
@@ -3,10 +3,15 @@
 
 #include <uapi/asm-generic/ioctl.h>
 
+#ifdef __CHECKER__
+#define _IOC_TYPECHECK(t) (sizeof(t))
+#else
 /* provoke compile error for invalid uses of size argument */
 extern unsigned int __invalid_size_argument_for_IOC;
 #define _IOC_TYPECHECK(t) \
 	((sizeof(t) == sizeof(t[1]) && \
 	  sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
 	  sizeof(t) : __invalid_size_argument_for_IOC)
+#endif
+
 #endif /* _ASM_GENERIC_IOCTL_H */
Signature · 1 line
2.0.0.rc0
#1 lore raw
Quoted 45 lines · On Fri, 09 May 2014 09:43:58 +0200 Hans Verkuil <[email protected]> wrote:

Andrew, can you merge this for 3.15 or 3.16 (you decide)? While it fixes a sparse error for the media subsystem, it is not really appropriate to go through our media tree.

Thanks,

Hans

When running sparse over drivers/media/v4l2-core/v4l2-ioctl.c I get these errors:

drivers/media/v4l2-core/v4l2-ioctl.c:2043:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2044:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2045:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2046:9: error: bad integer constant expression

etc.

The root cause of that turns out to be in include/asm-generic/ioctl.h:

#include <uapi/asm-generic/ioctl.h>

/* provoke compile error for invalid uses of size argument */ extern unsigned int __invalid_size_argument_for_IOC;

#define _IOC_TYPECHECK(t) \
        ((sizeof(t) == sizeof(t[1]) && \
          sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
          sizeof(t) : __invalid_size_argument_for_IOC)

If it is defined as this (as is already done if __KERNEL__ is not defined):

#define _IOC_TYPECHECK(t) (sizeof(t))

then all is well with the world.

This patch allows sparse to work correctly.

include/asm-generic/ioctl.h +2 -0
@@ -3,10 +3,15 @@
 
 #include <uapi/asm-generic/ioctl.h>
 
+#ifdef __CHECKER__
+#define _IOC_TYPECHECK(t) (sizeof(t))

include/asm-generic/ioctl.h line 17

Quoted 10 lines
include/asm-generic/ioctl.h +3 -0
+#else
 /* provoke compile error for invalid uses of size argument */
 extern unsigned int __invalid_size_argument_for_IOC;
 #define _IOC_TYPECHECK(t) \
 	((sizeof(t) == sizeof(t[1]) && \
 	  sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
 	  sizeof(t) : __invalid_size_argument_for_IOC)
+#endif
+
 #endif /* _ASM_GENERIC_IOCTL_H */

Can't we use BUILD_BUG_ON() here? That's neater, more standard and BUILD_BUG_ON() already has sparse handling.

author
#2 lore raw
Quoted 45 lines · Andrew Morton
Quoted 43 lines · On Fri, 09 May 2014 09:43:58 +0200 Hans Verkuil <[email protected]> wrote:

Andrew, can you merge this for 3.15 or 3.16 (you decide)? While it fixes a sparse error for the media subsystem, it is not really appropriate to go through our media tree.

Thanks,

Hans

When running sparse over drivers/media/v4l2-core/v4l2-ioctl.c I get these errors:

drivers/media/v4l2-core/v4l2-ioctl.c:2043:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2044:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2045:9: error: bad integer constant expression drivers/media/v4l2-core/v4l2-ioctl.c:2046:9: error: bad integer constant expression

etc.

The root cause of that turns out to be in include/asm-generic/ioctl.h:

#include <uapi/asm-generic/ioctl.h>

/* provoke compile error for invalid uses of size argument */ extern unsigned int __invalid_size_argument_for_IOC;

#define _IOC_TYPECHECK(t) \
        ((sizeof(t) == sizeof(t[1]) && \
          sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
          sizeof(t) : __invalid_size_argument_for_IOC)

If it is defined as this (as is already done if __KERNEL__ is not defined):

#define _IOC_TYPECHECK(t) (sizeof(t))

then all is well with the world.

This patch allows sparse to work correctly.

include/asm-generic/ioctl.h +0 -0
@@ -3,10 +3,15 @@
 
 #include <uapi/asm-generic/ioctl.h>
Quoted 15 lines

include/asm-generic/ioctl.h line 17

Quoted 12 lines
include/asm-generic/ioctl.h +5 -0
+#ifdef __CHECKER__
+#define _IOC_TYPECHECK(t) (sizeof(t))
+#else
 /* provoke compile error for invalid uses of size argument */
 extern unsigned int __invalid_size_argument_for_IOC;
 #define _IOC_TYPECHECK(t) \
 	((sizeof(t) == sizeof(t[1]) && \
 	  sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
 	  sizeof(t) : __invalid_size_argument_for_IOC)
+#endif
+
 #endif /* _ASM_GENERIC_IOCTL_H */

Can't we use BUILD_BUG_ON() here? That's neater, more standard and BUILD_BUG_ON() already has sparse handling.

I don't think so. BUILD_BUG_ON is not meant to be used in an expression, whereas _IOC_TYPECHECK(t) is (it should return sizeof(t)).

This looked promising at first sight:

#define _IOC_TYPECHECK(t) \
        ({BUILD_BUG_ON(sizeof(t) == sizeof(t[1]) && sizeof(t) < (1 << _IOC_SIZEBITS)); \
         sizeof(t);})

But it leads to 'case label does not reduce to an integer constant' compile errors.

And a typical ioctl define expands to this horror:

case (((2U) << (((0 +8)+8)+14)) | ((('M')) << (0 +8)) | (((1)) << 0) | (((({do { bool __cond = !(!(sizeof(int) == sizeof(int[1]) && sizeof(int) < (1 << 14))); extern void __compiletime_assert_1909(void) __attribute__((error("BUILD_BUG_ON failed: " "sizeof(int) == sizeof(int[1]) && sizeof(int) < (1 << _IOC_SIZEBITS)"))); if (__cond) __compiletime_assert_1909(); do { } while (0); } while (0); sizeof(int);}))) << ((0 +8)+8))):

which also explains the errors: case labels with function calls in them won't compile.

So I think my proposed patch is the best approach.

Regards,

Hans