Re: .align problem with i[34]86-*-coff

[Rotter Klaus <Klaus dot Rotter at erl9 dot siemens dot de>]

Hello,

first sorry for mixing up my message with Andreas Jaegers one.

> For debugging reasons I have tried to set up a clean enviroment compiling both binutils 
> and
> gcc for i386-unkown-aout (2.95.1). Compiling works, but it turned out that the is a bug
> with structures. My RTOS didn't allow padding bytes in structures, so I use the flag 
> -fpack-struct. This worked fine with i586-pc-cygwin, but with i386-unkown-aout gcc aligns
> 32-bit ints in structures to a longword boundary (even with -fpack-struct). 

I digged a little deeper into this problem. I have two compilers, one configured 
with i386-pc-cygwin32 (build on my own) and the other i586-pc-cygwin (the original
cygwin update by Mumit Khan). Then I have compiled the following program:

typedef struct {
    char    *ptr;
    short   s1;
    char    *ptr2;
    short   s2;
    int     flags;
} ST;
ST st = { "Hello", 1, "You", 2, 123456 };

(Well, not really a programm, just a structure)

Compiling with "i586-pc-cygwin32-gcc -S -fpack-struct struct.c" (2.95) gives me:

	.file	"struct.c"
gcc2_compiled.:
___gnu_compiled_c:
.globl _st
.data
_st:
	.long LC0
	.word 1
	.long LC1
	.word 2
	.long 123456
.text
LC1:
	.ascii "You\0"
LC0:
	.ascii "Hello\0"

Compiling with "i386-pc-cygwin32-gcc -S -fpack-struct struct.c" (2.95.1) gives me:

	.file	"struct.c"
gcc2_compiled.:
___gnu_compiled_c:
.globl _st
.data
	.align 4
_st:
	.long LC0
	.word 1
	.space 2
	.long LC1
	.word 2
	.space 2
	.long 123456
.text
LC1:
	.ascii "You\0"
LC0:
	.ascii "Hello\0"

So, either there is a new bug introduced between 2.95 and 2.95.1 (I don't believe 
that), or alignment inside structures depends on the processor you choose without
regarding a -fpack-struct option. This is bad, I think it is a bug, because the 
the longword alignment is _not_ needed on a i386 or i486, it is only faster (on a 
i486, I think). 

Unfortunatly, I wasn't able to compare two releases (eg. 2.95.1 compiled for 
i386-pc-cygwin and i586-pc-cygwin) because my eviroment is so slow. A gcc build
"make LANGUAGES=c" takes about 2h ;-(. I am still waiting to get it ready...

-- 
 Klaus Rotter, Siemens AG,  ATD TD 6 EPG, Postfach 3249, 91020 Erlangen
 Tel.: +49 9131 18-84637, Fax: +49 9131 18-84648 
 mailto:Klaus.Rotter@erl9.siemens.de