Sender: rich AT phekda DOT freeserve DOT co DOT uk
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Date: Tue, 20 Jun 2000 22:04:52 +0100
From: Richard Dawe <rich AT phekda DOT freeserve DOT co DOT uk>
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To: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
CC: djgpp AT delorie DOT com, rich AT phekda DOT freeserve DOT co DOT uk
Subject: Re: Inline asm: lcall & various binutils versions
References: <39060495 DOT 8CA597B0 AT bigfoot DOT com> <39069F55 DOT 639FE192 AT is DOT elta DOT co DOT il> <39341DE2 DOT 20CA1843 AT bigfoot DOT com> <200005302109 DOT AAA27505 AT alpha DOT netvision DOT net DOT il> <394E733C DOT FE5BAB89 AT phekda DOT freeserve DOT co DOT uk> <200006201739 DOT UAA28575 AT mailgw1 DOT netvision DOT net DOT il>
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Reply-To: djgpp AT delorie DOT com

Hello.

Eli Zaretskii wrote:
> Thanks for looking into this.

No worries - sorry it took a while. ;) It's a problem that affects quite a
few things I think - DJGPP (as discussed on djgpp-workers), libsocket,
libwin, probably others.

> > The answer seems to be that there is no easy way.
> 
> Gosh, I _hate_ incompatible changes that don't leave any escapes like
> a command-line option to get the old behavior!

Yes, it's a big PITA. =(

> > 3. Detect which version of binutils is being used and adjust the code
> > appropriately. Perhaps the most likely, but ugly in terms of code. :(
> 
> This sounds like the lesser-evil solution.

Yep, I left the best solution until last. 8)

> Here's a starting point for Makefile magic to do that:
> 
>   BNU_VERSION := $(shell as --version | sed -n 's/^GNU assembler //p')
> 
> (This is only a starting point, since you will need to define
> BNU_MAJOR, BNU_MINOR and such likes, given BNU_VERSION.)
> 
> Then use "gcc -DBNU_MINOR=..." to get this info into the
> preprocessor.

How about this:

---Start Makefile---
#
# Makefile for bnuver
#

SHELL = /bin/sh

GAS_VERSION    := $(shell as --version | sed -n 's/^GNU assembler //p')
GAS_MAJOR      := $(shell   echo $(GAS_VERSION) \
                          | sed -n 's/^\([0-9]*\).*/\1/p')
GAS_MINOR      := $(shell   echo $(GAS_VERSION) \
                          | sed -n 's/^[0-9]*\.\([0-9]*\).*/\1/p')
GAS_MINORMINOR := $(shell   echo $(GAS_VERSION) \
                          | sed -n 's/^[0-9]*\.[0-9]*\.\([0-9]*\).*/\1/p')

CFLAGS += -save-temps
CFLAGS += -DGAS_MAJOR=$(GAS_MAJOR)
CFLAGS += -DGAS_MINOR=$(GAS_MINOR)
CFLAGS += -DGAS_MINORMINOR=$(GAS_MINORMINOR)

default:	display-flags asmifdef

display-flags:
	@echo gas version $(GAS_VERSION) '->' \
	      $(GAS_MAJOR) $(GAS_MINOR) $(GAS_MINORMINOR)
	@echo 'CFLAGS =' $(CFLAGS)
---End Makefile---

---Start asmifdef---
int main (int argc, char *argv[])
{
	__asm__ ("nop	\r\n"
#if GAS_MAJOR >= 2 && GAS_MINOR > 8
		 "nop	\r\n"
#endif	/* IFDEFTEST */
		 "nop	\r\n");
}
---End asmifdef---

I tested this with binutils 2.9.5.0.22 with sed 3.02 on Linux (where as
says '2.9.5' as the version) and it appears to work.

I used GAS_* here, because it could be different to the version of
binutils, plus it's the thing we're actually concerned with. I think
there's enough granularity in version number to go round there. ;) Is this
satisfactory? My sed knowledge is limited (*), but this seems to do the
trick.

(*) I always try to use Perl regexps and it fails. :(

I'll use this to fix up libsocket, libwin with this sometime.

It took me a while to work out how to put #ifdefs in inline assembly. Eli,
you probably knew this already, but: You have to rely on C's string
concatenation.

[ If you put '#ifdef' in the inline assembly, then it becomes an assembly
comment and does nothing. ;) I couldn't see a way to propagate -DSOMETHING
into the assembly so that '.ifdef SOMETHING' could be used. ]

This feels like less of a hack than relying on gas to generate the right
code in spite of a warning.

Bye,

-- 
Richard Dawe
[ mailto:richdawe AT bigfoot DOT com | http://www.bigfoot.com/~richdawe/ ]