Re: fopen64 and friends as aliases

["writeonce@midipix.org" <writeonce@midipix.org>]

On 04/15/2014 03:15 PM, Rich Felker wrote:
> 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
>
>
Thanks for the explanation, these are indeed great reasons to stick with 
#define for all of the "64" functions.

As far as llvm goes, and for what it's worth: my own patch of 
llvm/Target/TargetLibraryInfo.h simply #undefines fopen64, etc., which 
allows keeping all of the header's original code intact.  With llvm-3.4 
and using a native musl compiler (gcc-4.8.2), that was the only patch 
required (tweaking excluded) for the entire thing to compile and build 
(so no need to further patch TargetLibraryInfo.cpp, etc.)

zg