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Re: bal instruction in gcc 3.x

To: Kishore K <hellokishore@gmail.com>
Subject: Re: bal instruction in gcc 3.x
From: Pete Popov <ppopov@embeddedalley.com>
Date: Tue, 19 Jul 2005 12:53:06 -0700
Cc: Ralf Baechle <ralf@linux-mips.org>, "'linux-mips@linux-mips.org'" <linux-mips@linux-mips.org>
In-reply-to: <f07e6e05071910194bab9b16@mail.gmail.com>
Organization: Embedded Alley Solutions, Inc
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <f07e6e05071909301c212ab4@mail.gmail.com> <20050719164427.GB8758@linux-mips.org> <f07e6e05071910194bab9b16@mail.gmail.com>
Reply-to: ppopov@embeddedalley.com
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Try the attached patch instead.

Pete

On Tue, 2005-07-19 at 22:49 +0530, Kishore K wrote:
> On 7/19/05, Ralf Baechle <ralf@linux-mips.org> wrote:
> > On Tue, Jul 19, 2005 at 10:00:20PM +0530, Kishore K wrote:
> > 
> > > We are facing a problem when U-boot is compiled with gcc 3.x
> > >
> > > U-boot  uses the following instruction in one of the files.
> > >
> > > bal jump_to_symbol
> > >
> > > This code gets compiled without any problem with gcc2. However, if I
> > > compile the code
> > > with gcc3, it exits with the error "Cannot branch to unknown symbol".
> > >
> > > What should we do to circumvent this problem ?
> > >
> > > I replaced
> > >
> > > bal jump_to_symbol
> > >
> > > by
> > >
> > > la t9, jump_to_symbol
> > > jalr t9
> > >
> > > Then code gets compiled properly without any problem. Please let me
> > > know, whether this
> > > is correct way of fixing the problem. I am newbie to MIPS assembly
> > > language. Why this
> > > change is required with gcc 3.x compiler ?
> > 
> > FIrst of all, gcc doesn't care at all about your assembler code, that's
> > the assembler which you must have changed along with that.
> > 
> > There used to be no relocation type to represent a branch to an external
> > symbol in an ELF file which is why gas is throwing an error message, so
> > gas is throwing an error message.  Latest gas fixed that shortcoming.
> > I think there was a bug in somewhat older gas which resulted in such
> > invalid code actually being accepted even though it shouldn't have been.
> > 
> >   Ralf
> 
> Thank you very much for the reply.
> 
> First of all code got compiled only after removing the option
> -mips-allow-branch-to-undefined from Makefile. If this option is
> included, compilation fails saying that option is invalid. I am using
> binutils-2.14.90.06.
> Same problem is observed even with binutils 2.15.94.0.2.2. 
> 
> Do you mean to say that no change is required in the code snippet 
> 
> bal jump_to_symbol
> 
> and code should get compiled with the latest assembler without any
> problem. Please clearify.
> 
> TIA,
> --kishore
> 

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