On Fri, Sep 28, 2012 at 4:20 PM, Daniel Santos <[email protected]> wrote:
> Negative sized arrays wont create a compile-time error in some cases
> starting with gcc 4.4 (e.g., inlined functions), but gcc 4.3 introduced
> the error function attribute that will. This patch modifies
> BUILD_BUG_ON to behave like BUILD_BUG already does, using the error
> function attribute so that you don't have to build the entire kernel to
> discover that you have a problem, and then enjoy trying to track it down
> from a link-time error.
Few other alternatives I've seen used in other projects (from memory,
so I may have gotten the details wrong):
1) if (condition) { __asm__(".error \"Some error message\""); }
2) switch (0) {
case 0: break;
case !condition: break;
}
(fails to compile if !condition evaluates to 0)
If you can get the first suggestion to work it'd be nice, as you could
get some descriptive error message (you can add the line number there
too).
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
On 10/01/2012 07:48 PM, Michel Lespinasse wrote:
> On Fri, Sep 28, 2012 at 4:20 PM, Daniel Santos <[email protected]> wrote:
>> Negative sized arrays wont create a compile-time error in some cases
>> starting with gcc 4.4 (e.g., inlined functions), but gcc 4.3 introduced
>> the error function attribute that will. This patch modifies
>> BUILD_BUG_ON to behave like BUILD_BUG already does, using the error
>> function attribute so that you don't have to build the entire kernel to
>> discover that you have a problem, and then enjoy trying to track it down
>> from a link-time error.
> Few other alternatives I've seen used in other projects (from memory,
> so I may have gotten the details wrong):
>
> 1) if (condition) { __asm__(".error \"Some error message\""); }
> 2) switch (0) {
> case 0: break;
> case !condition: break;
> }
> (fails to compile if !condition evaluates to 0)
>
> If you can get the first suggestion to work it'd be nice, as you could
> get some descriptive error message (you can add the line number there
> too).
Thanks for this info. I'm still pretty noob-ish in modern assembly, but
is the .error directive available on all supported assemblers? It
appears to have been added to GNU binutils in version 2.16 from what I
can tell (http://sourceware.org/binutils/docs-2.16/as/Error.html). If
it is supported, I would definitely prefer that one as a fallback option.
I did a search on sources for the regex \.error\s+\\?" and didn't turn
up anything outside of arch/, so I'm guessing this may not be completely
portable. Note also that these BUILD_BUG* macros do emit an error
message on gcc 4.3+ using __attribute__((error("msg"))).
Daniel