Artsize still not quite right in CURRENT
qralston+ml.inn-workers at andrew.cmu.edu
Thu Apr 19 04:47:36 UTC 2001
On 18 Apr 2001, Alex Kiernan wrote:
> I found a RedHat 7 box to play on here, and whilst it needs a
> #include <stdint.h> to get the uint32_t type, when run it gives:
> pread broken - wrote badc0de, read deadbeef
> [BTW someone who knows Linux better than me - should this build line
> do the right thing:
> gcc -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 checkpread.c]
Close, but not quite. You're getting bitten because without at least
"-D_XOPEN_SOURCE=500" (as per the pread man page), the definitions of
the pread/pwrite functions are essentially commented out of unistd.h.
You can see what's happening if you turn on warnings:
$ gcc -Wall -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 checkpread.c
checkpread.c: In function `main':
checkpread.c:38: warning: implicit declaration of function `pread'
Because pread isn't declared, the -D_FILE_OFFSET_BITS=64 doesn't have
a chance to apply to it, so when you link you wind up with the 32-bit
version of pread.
Since defining _XOPEN_SOURCE to 500 or greater automatically triggers
_LARGEFILE_SOURCE, this is the compilation command you want:
$ gcc -Wall -D_XOPEN_SOURCE=500 -D_FILE_OFFSET_BITS=64 checkpread.c
I compiled checkpread.c on a Red Hat 7.1 system using the above
compilation command, and when run it does the correct thing (that is,
it produces no output).
Really, I don't see any reason why INN shouldn't be compiled with the
_GNU_SOURCE feature test macro on any system where the GNU C Library
is detected. This is what glibc recommends. To quote glibc:
- Macro: _GNU_SOURCE
If you define this macro, everything is included: ISO C89,
ISO C99, POSIX.1, POSIX.2, BSD, SVID, X/Open, LFS, and GNU
extensions. In the cases where POSIX.1 conflicts with BSD,
the POSIX definitions take precedence.
We recommend you use `_GNU_SOURCE' in new programs. If you
don't specify the `-ansi' option to GCC and don't define any of
these macros explicitly, the effect is the same as defining
`_POSIX_C_SOURCE' to 2 and `_POSIX_SOURCE', `_SVID_SOURCE', and
`_BSD_SOURCE' to 1.
You'll still need -D_FILE_OFFSET_BITS=64, though; _GNU_SOURCE doesn't
automatically trigger that.
James Ralston, Information Technology
Software Engineering Institute
Carnegie Mellon University, Pittsburgh, PA, USA
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