From: NoEmailAds AT execpc DOT com (Chris Giese)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Still a few questions about relocating COFF symbols (dynamic loading)
Date: Wed, 24 Jul 2002 02:29:00 GMT
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dshnv AT www DOT com (dshnv) wrote:

{some code}

>int global_bss;

If you use GNU C, non-initialized non-static non-extern globals are
actually "common" variables. The linker allocates space for these,
not the compiler.

Turbo C, Microsoft C, etc. don't support common variables.

>int main()
>{
>     int foo, bar;

Auto (non-static local) variables are stored on the stack. They
don't need relocation, so they don't appear in the symbol table
used for relocation. They may appear in one of the _debug_
sections, depending on the debug format used.

>Is it right that I can just leave these _foo and _bar variables alone,
>that I don't have to perform any kind of relocation, but just ignore
>them?

Correct.

>If not, how am I to figure the real size of the .bss if the
>section header sais the .bss is 0 bytes in size.

Your relocation code must support common variables. If not, the
relocatable code can be linked into a new relocatable file
using the "-r" and "-d" options to ld:
	ld -d -r -o new_object_file.o object_file.o

>I already know that global_bss does not appear in the .bss but is
>defined as member of the [common] section.

The linker command above combines [common] into .bss for relocatable
files. From the 'ld' info page:

`-d'	`-dc'	`-dp'
     These three options are equivalent; multiple forms are supported
     for compatibility with other linkers.  They assign space to common
     symbols even if a relocatable output file is specified (with
     `-r').  The script command `FORCE_COMMON_ALLOCATION' has the same
     effect.  *Note Miscellaneous Commands::.

And here's a program that loads and runs a relocatable version
of Tetris:
	http://www.execpc.com/~geezer/osd/exec/runreloc.zip
It also works with ELF and Win32 PE COFF.

-- 
geezer@    | http://www.execpc.com/~geezer
execpc.com | http://www.execpc.com/~geezer/osd