[Bug libc/29399] Wrong definition of setjmp

["fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29399

--- Comment #8 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Zack Weinberg from comment #6)
> I don't think the standard is ambiguous at all.  Its wording could be
> improved, but there's only one interpretation that makes sense.
> 
> Since at least C11, section 7.1.3p2 reads in part
> 
> > If the program declares or defines an identifier in a context in which it is reserved (other than as allowed by 7.1.4), **or defines a reserved identifier as a macro name**, the behavior is undefined.
> 
> The clause set off by double asterisks doesn't make any sense unless "a
> reserved identifier" is understood broadly: if the program defines an
> identifier that is reserved *in any context* as macro name, the behavior is
> undefined.

On the other hand, 6.2.1p1 refuses to define scope for macro names and macro
parameters, so it's hard to see how the an “identifier with file scope” could
refer to a macro name.

I think 7.1.3 leaves something to be desired anyway because it makes it pretty
clear that this is valid:

#define tm_sec puts ("Hello, world!")
#include <time.h>

int
main (void)
{
  tm_sec;
  return 0;
}

But to implement that, we would have to use non-standard preprocessor features
(#pragma push_macro, #pragma pop_macro).

(Historically, structure fields had file scope (similar to some ML flavors),
but that hasn't been true for a long, long time.)

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