Re: Trouble with alloca.h

On 17/02/19 17:17, Eli Zaretskii wrote:
> The new header alloca.h defines 'alloca' unconditionally as (AFAIU) an
> inline function:
> 
>   __CRT_ALIAS void *alloca( size_t __n )
>   { return __builtin_alloca( __n ); }

Yes, that's an inline function, which is *always* expanded in-line;
according to GCC's info, this makes it equivalent to a macro, in terms
of both speed, and code size.  However, it also has advantages over a
macro, in terms of type safety, (maybe not so important in this case,
because __builtin_alloca() should be type safe anyway), but rather more
importantly here, it also supports C++ namespace qualification, (which a
macro does not), should any user wish to so qualify it.

> This caused me trouble while building a GNU package, because Gnulib's
> alloca.h makes 'alloca' a macro:
> 
>   #ifndef alloca
>   # ifdef __GNUC__
>   #  define alloca __builtin_alloca

So, yet another endemic Gnulib bug.

> I'm not yet sure why Gnulib decides that it needs to use its own
> alloca.h,

It should not do so; it should defer to the host platform's own
implementation, when one is provided.

> but I know that many packages do the above regardless, when
> the compiler is GCC.

And such packages are similarly broken.

> Should MinGW's alloca.h perhaps be more defensive,

It could be, but...

> and only define its
> own version if 'alloca' is not already defined as a macro?

this isn't the way; it should simply, and unilaterally, override the
endemic brain damage in packages such as Gnulib, and just #undef any
pre-existing, conflicting macro definition.

-- 
Regards,
Keith.

Public key available from keys.gnupg.net
Key fingerprint: C19E C018 1547 DE50 E1D4 8F53 C0AD 36C6 347E 5A3F

_______________________________________________
MinGW-Users mailing list
[email protected]

This list observes the Etiquette found at
http://www.mingw.org/Mailing_Lists.
We ask that you be polite and do the same.  Disregard for the list etiquette may cause your account to be moderated.

_______________________________________________
You may change your MinGW Account Options or unsubscribe at:
https://lists.osdn.me/mailman/listinfo/mingw-users
Also: mailto:[email protected]?subject=unsubscribe

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.20 (GNU/Linux)
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=o5mz
-----END PGP SIGNATURE-----