[Mingw-notify] [ mingw-Bugs-614067 ] need pack/alignment attribute in stat.h

[<no...@so...>]

Bugs item #614067, was opened at 2002-09-24 22:52
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=102435&aid=614067&group_id=2435

Category: MinGW
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Dave Spring (dspring)
Assigned to: Earnie Boyd (earnie)
Summary: need pack/alignment attribute in stat.h

Initial Comment:
MingGW 2.0.0
using gcc -fpack-struct breaks stuff.
My particular problem is sts/stat.h the alignment
for st_rdev gets overriden.
MSVCRT clearly uses quadbyte alignment for stat.

The fix is somewhere around lines 113,129
- change to:

	short	st_gid ;		/* Group: 
Ditto */
  
	_dev_t	st_rdev __attribute__ ((aligned 
(4)));	/* Seems useless (not even filled in) */
	_off_t	st_size;	/* File size in bytes */

twice for stat and _stat

It might be worth scheduling a review for other 
structures.

test program/demonstration attached.

Oh yes - the symptom is that file sizes are gibberish,
since mingw thinks that st_size starts 2 bytes earlier
due to the pack-struct.

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>Comment By: Dave Spring (dspring)
Date: 2002-09-25 10:19

Message:
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I have read the doc.
I'm trying to port libdvdread to win32. So have to match 
legacy binary files. Hence I don't want to adorn someone 
else's header files with GCC/Mingw specific #pragma or 
__attribute__. In a new program I would workaround it by
compiling the packed stuff separately and making sure
it doesn't invoke any libraries.
Anyway, the point is that the mingw header files don't 
accurately describe the interface to the lib files (including
 the alignment) which is their sole purpose. 
I you disagree. Fine. Please at least put an entry in the FAQ
with the symptom to help others.

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Comment By: Danny Smith (dannysmith)
Date: 2002-09-25 00:30

Message:
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Have you read the doc's for -fpack-struct?

-fpack-struct 
Pack all structure members together without holes. 
Usually you would not want to use this option, since it 
makes the code suboptimal, and the offsets of structure 
members won't agree with system libraries. 

in new gcc, the warning is slightly different:

[from invoke.texi]
@strong{Warning:} the @option{-fpack-struct} switch 
causes GCC to generate
code that is not binary compatible with code generated 
without that switch.
Additionally, it makes the code suboptimial.
Use it to conform to a non-default application binary 
interface.

Danny



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