Re: [PATCH] compiler.h: fix error in BUILD_BUG_ON() reporting

[Daniel Santos <daniel.santos@pobox.com>]

On 3/31/20 2:08 PM, Vegard Nossum wrote:
>
> __LINE__ is only used currently for creating a unique identifier, as far
> as I can tell.
>
> The way it works is that it creates a function declaration with the
> attribute __attribute__((error(message))), which makes gcc throw an
> error if the function is ever used (i.e. calls are not compiled out).

Back before __attribute__((error())), these macros used to just declare
a function that isn't defined and you only got an error at link-time --
the line number did matter then.  Then there was the negative array
index thing.

>
> The number does appear in the output, but it's not even really obvious
> that it's a line number. And the compiler's diagnostics are pretty good
> at showing the whole "stack trace" of where the call came from
> (including the proper line numbers).
>
>
> Vegard

And the stack trace used to be useless without -g or -g3, but I believe
gcc gives the macro expansion back trace without it now.  But imo, the
macro expansion back trace is a lot of noise that we can eliminate with
a direct gcc mechanism to break the build on some __builtin_constant_p()
expression.

Daniel