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SubjectRe: [PATCH v3 0/2] Stop some of the abuse of BUG() where compile time checks should be used.
On 11/23/2011 03:57 PM, Linus Torvalds wrote:
> Btw, would it possibly make sense to make the string more useful?
> For example using __FILE__ and __LINE__, or possibly letting the user
> of the BUILD_BUG() give a string ("Using HMASK without

We thought about doing that, but without doing some complex preprocessor
fu, the GCC attribute ((error())) thing doesn't do what we want.

It appears that if more than a single instance of the construct is used
in a compilation unit, the string emitted by the compiler for any of the
violations will be the last string encountered.

So if you did something like:

Line 99: BUILD_BUG("You failed on line 99");
Line 666: BUILD_BUG("You failed on line 666");

The message emitted for a failure at line 99 would be "You failed on
line 666". Which is probably worse than no message at all.

It may be possible to do something like:

#define _LINENAME_CONCAT( _name_, _line_ ) _name_##_line_
#define _LINENAME(_name_, _line_) _LINENAME_CONCAT(_name_,_line_)

do { \
extern void FUBAR (void) \
__linktime_error("BUILD_BUG failed: " MSG); \
FUBAR (); \
} while (0)

#define BUILD_BUG(M,A) _BUILD_BUG(M, _LINENAME(__build_bug_failed,__LINE__))

But it didn't seem worth it.

> Whatever. It's bikeshedding - what would probably be more important
> would be to get this into linux-next so that we find out whether there
> are any compile issues with it on other platforms or compiler
> versions.
> Linus

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