Re: [Nasm-devel] Incorrect bss section sizes in COFF output

[Josef D. <jo...@ge...>]

Frank Kotler wrote:
> Josef Drexler wrote:
> 
>>  > nasm -f coff -o cofftest.o cofftest.asm
>>  > objdump -h cofftest.o
>>
>> cofftest.o:     file format pe-i386
> 
> 
> Whoa! "-f coff" shouldn't be creating "pe" files, should it?

Well, PE and COFF are two variations on a theme.  The structure is very 
similar, anyway.

> ...
> 
>> (made by GNU ld)
> 
> Which GNU ld, exactly?

i686-pc-mingw-ld version 2.15.94 20041229 (running on Linux).

> If it's Mingw/Cygwin, try "-f win32" and see if 
> that solves the problem. If it's djgpp's ld, "-f coff" should be right, 
> but I'm not sure where the "pe" is coming from...

That part of outcoff.c is the same for win32/coff.  I did find out 
eventually that I needed to use "-f win32" to get the relocations right, 
though, but for the section metadata it makes no difference other than 
the section flags.

> You may have discovered something, and we certainly appreciate the 
> proposed fix(!!!), but I'm confused about "which COFF" you're using. 
> There's another potential issue... earlier versions of Mingw's ld did it 
> like MS documented it, which is not the way they *did* it! This was 
> blamed on a Nasm bug, but ld changed its handling of the "virtual size", 
> and now Nasm's okay :) (I forget version numbers - November of 2003, I 
> think???) If you've got an older version of (Mingw/Cygwin) ld, a newer 
> version might make a difference.

I'll try that.

> If either of these things turned out to be the problem, it would be even 
> easier than applying your fix! :)

After some experimenting with GNU as, I found that it always sets vsize=0:

gcc/as:

NAME	VSIZE	VADDR	DSIZE	OFS	RELOFS	LINEOFS	NREL	NLINE	FLAGS
.text	0	0	20h	8Ch	1ECh	0	2	0	60000020
.data	0	0	140h	ACh	0	0	0	0	C0000040
.bss	0	0	30h	0	0	0	0	0	C0000080

nasm/coff:

NAME	VSIZE	VADDR	DSIZE	OFS	RELOFS	LINEOFS	NREL	NLINE	FLAGS
.text	0	0	12h	8Ch	9Eh	0	2	0	00000020
.data	12h	0	140h	B2h	1F2h	0	0	0	00000040
.bss	152h	0	28h	0	0	0	0	0	00000080

nasm/win32:
NAME	VSIZE	VADDR	DSIZE	OFS	RELOFS	LINEOFS	NREL	NLINE	FLAGS
.text	0	0	12h	8Ch	9Eh	0	2	0	60500020
.data	12h	0	140h	B2h	1F2h	0	0	0	C0300040
.bss	152h	0	28h	0	0	0	0	0	C0300080

So as far as section headers are concerned, coff and win32 differ only 
in the flags, which seem to be correct for both.

According to http://www.xaff.org/GI/COFF/coff.html, the vsize should be 
zero for all object files, and is only set for actual linked 
executables.  When I change outcoff.c to always set vsize=0, the linked 
exectuables are fine too.

I'm not sure however whether there are people who need the old vsize 
behaviour.  The text at the beginning of outcoff.c makes it clear that 
it was intentional, so it might not be the best idea to just change it 
like that without better understanding of the reasoning behind it.

Perhaps this calls for a third coff output type?

-- 
Josef Drexler