Re: Trouble with alloca.h

On 18/02/19 03:31, Eli Zaretskii wrote:
>> it should simply, and unilaterally, override the endemic
>> brain damage in packages such as Gnulib, and just #undef any 
>> pre-existing, conflicting macro definition.
>
> That should also work, but it might mean part of the offending package
> is compiled with "the other" definition of alloca, which could cause
> some subtle problem?

That should make no difference whatsoever; in either case the same
compiler intrinsic should be expanded in-line, yielding identically the
same object code for both.  The problem with the pre-emptive definition
of alloca as a macro:

  #define alloca __builtin_alloca

means the the subsequent in-line function definition would become:

  __CRT_ALIAS void *__builtin_alloca( size_t __n )
  { return __builtin_alloc( __n ); }

which, if it were allowed, would recurse ad-infinitum, at the point of
expansion.  Of course, it isn't allowed, because recursive functions are
not capable of in-line expansion, and __builtin_alloca() *must* be so
expanded.  Even if this disallowed expansion weren't sufficient to
prevent successful compilation, it is also questionable whether the
redefinition of the compiler intrinsic would be permitted.

-- 
Regards,
Keith.

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