[LTP] reason of pwritev01_64 failure on 32-bit arm

[Jan Stancek]

----- Original Message -----
> From: "Nikita Yushchenko" <nyushchenko@dev.rtsoft.ru>
> To: ltp@lists.linux.it
> Cc: "arusalin" <arusalin@dev.rtsoft.ru>
> Sent: Friday, 2 September, 2016 5:58:51 PM
> Subject: [LTP] reason of pwritev01_64 failure on 32-bit arm
> 
> Hi,
> 
> I've reproduced and analyzed failure of pwritev01_64 described at [1]
> 
> [1] http://lists.linux.it/pipermail/ltp/2016-March/001201.html
> 
> 
> pwritev01_64 fail is an LTP issue
> 
> pwrite01 and pwrite01_64 are built from the same source, pwrite01.c
> 64-bit version is built with additional define, -D_FILE_OFFSET_BITS=64,
> which causes 'off_t' type defined by glibc to become 64-bit.
> 
> Problem is that both pwrite01.o and pwrite01_64.o link against the same
> utility library, libltp
> From this library, a routine called safe_pread() is used.
> One of arguments of this routine has type off_t.
> This means that ABI for this routine is different when built with
> -D_FILE_OFFSET_BITS=64 and without it.
> Library is built without -D_FILE_OFFSET_BITS=64, thus on 32-bit platform
> safe_pread() inside library expects ABI with 32-bit 'off_t'. And
> pwrite01_64.o, built with -D_FILE_OFFSET_BITS=64, uses different ABI.
> 
> If a copy of safe_pread() is injected inside pwrite01.c (and compile
> issue is resolved), test passes.
> 
> In general, it is not safe to link together object files built with and
> without -D_FILE_OFFSET_BITS=64, since that code is not always
> binary-compatible.
> 
> 
> On 64-bit platform, sizeof(off_t) is 8 both with and without
> -D_FILE_OFFSET_BITS=64, this issue does not show.

Hi,

Thanks for following up on this. Looks like we should do same thing for
pread/pwrite as we already do for lseek, that is to move these
from lib to headers as inline functions:

$ grep -B2 off_t -r lib/*.c
lib/safe_macros.c-ssize_t safe_pread(const char *file, const int lineno, void (*cleanup_fn)(void),
lib/safe_macros.c-                 char len_strict, int fildes, void *buf, size_t nbyte,
lib/safe_macros.c:                 off_t offset)
--
lib/safe_macros.c-ssize_t safe_pwrite(const char *file, const int lineno,
lib/safe_macros.c-                  void (cleanup_fn) (void), char len_strict, int fildes,
lib/safe_macros.c:                  const void *buf, size_t nbyte, off_t offset)

Are you planning to submit a patch?

Regards,
Jan

> 
> WBR,
> Nikita Yushchenko
> 
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