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Re: bal instruction in gcc 3.x

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: bal instruction in gcc 3.x
From: Kishore K <hellokishore@gmail.com>
Date: Tue, 19 Jul 2005 22:49:48 +0530
Cc: linux-mips@linux-mips.org
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Reply-to: Kishore K <hellokishore@gmail.com>
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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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