Re: fopen64 and friends as aliases

[Rich Felker <dalias@aerifal.cx>]

On Tue, Apr 15, 2014 at 03:03:54PM -0400, writeonce@midipix.org wrote:
> On 04/15/2014 10:21 AM, Rich Felker wrote:
> >On Tue, Apr 15, 2014 at 06:59:46AM -0700, writeonce@midipix.org wrote:
> >>    Greetings,
> >>    I could not find in the archives any discussion of the above topic, and
> >>    was therefore wondering: would it be possible to have fopen64 and friends
> >>    (fseeko64, ftello64, tmpfile64) as aliases of the non-prefixed functions,
> >>    rather than having them #define'd as synonyms?  This will make most of the
> >>    musl-llvm patch unnecessary, and could probably help with other packages
> >>    as well.
> >>    Kind regards,
> >>    zg
> >For some of them like stat64, the #define is necessary anyway since
> >there is a struct that also needs to be mapped. So it's not so simple.
> >In any case, the aliases already exist for binary compatibility, but
> >some of them would be masked by these defines even if we declared them
> >in the public headers.
> >
> >Really what you're asking for is just a workaround of a nonsensical
> >bug in llvm, which should just be fixed. There is no excuse for the
> >hack they're doing with namespaces; instead the names should just be
> >properly prefixed to avoid clashing.
> 
> I understand. In that case, and for those functions that do not
> require an extra structure mapping, what is the advantage of
> 
> 	#define fopen64 fopen
> 
> over
> 
> 	FILE *fopen64 (const char *__restrict, const char *__restrict);
> 
> If the weak alias is already there anyway, then using the latter
> should only "penalize" (by adding a reference to the extra symbol)
> those apps/libs that use fopen64 in the first place. Is that
> correct?

There are three main advantages in my mind:

1. Lack of an extra set of prototypes that might need to be correct
   and which might not get tested well.

2. Avoiding putting references to the nonsense "64" symbols in the
   resulting binaries, so that the "64" symbols remain part of the
   ABI-compat layer (which could, in theory, be optional at build time
   somewhere in the future) rather than part of the public libc API.

3. Consistency: due to the need for #define stat64 stat (and perhaps
   others like this), using separate prototypes for the "64 functions
   would result in inconsistency in the binaries using them; some
   symbols would be referenced in the "64" version and others
   wouldn't. (And likewise, the "llvm bug" would manifest for some of
   them but not others.)

Rich