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Re: GAS m68k-aout relocation bug ?

From: Vincent Rivière
Subject: Re: GAS m68k-aout relocation bug ?
Date: Tue, 18 Nov 2003 09:16:49 +0100

> > - If the resulting address is still 16-bit wide, the constant is
> > silently relocated. In my example, the constant is 3. When I load
> > the resulting program, after the bogus-relocation, the constant
> > changes to 0x7f1f (so the value of the constant is invalid, and
> > depends on where the program is located in memory).
> OK, that answers the question of whether the linker generates > correct
> output.  It does not.  That means that this is a real bug.
> I would say that it is an assembler bug, as you suggested initially.
> However, I don't have any particular suggestions as to where to look
> to fix it.  For a BFD_ASSEMBLER gas, the routine fixup_segment() in
> gas/write.c should avoid emitting a reloc for a reference to a symbol
> which is defined.  I think fixup_segment() is also called for the
> m68k-aout target; I don't know why it isn't skipping this reloc.


For now, this bug isn't blocking thanks to the define-before-use workaround. 
When I have time, I'll take a closer look to the  GAS m68k-aout relocating 
routines and "=" operator. If I find how to fix the bug, I'll post the patch 

The only real problem is that this bug may be present in all m68k-aout targets. 
If so, bogus relocations will be generated on the test-case described here, and 
invalid constants may be silently emitted by the linker. Note that it is the 
case in GCC m68k fpu-emulation routines...

Thank you for your help.


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