PATCH: Fix gas/mips

["H. J. Lu" <hjl at lucon dot org>]

On Sun, Sep 29, 2002 at 01:13:57PM -0700, H. J. Lu wrote:
> On Sun, Sep 29, 2002 at 08:48:08AM -0700, H. J. Lu wrote:
> > On Sun, Sep 29, 2002 at 08:20:21AM -0700, H. J. Lu wrote:
> > > On Sat, Sep 28, 2002 at 07:16:53PM -0700, H. J. Lu wrote:
> > > > On Sat, Sep 28, 2002 at 10:13:17PM -0400, Daniel Jacobowitz wrote:
> > > > > On Sat, Sep 28, 2002 at 04:17:04PM -0700, H. J. Lu wrote:
> > > > > > I recompiled my mipsel kernel with binutils in CVS as of 20020928. The
> > > > > >  resulting kernel doesn't work. I got
> > > > > > 
> > > > > > Unhandled kernel unaligned access in unaligned.c::emulate_load_store_insn,
> > > > > > line:
> > > > > > $0 : 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000    
> > > > > > $8 : 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000    
> > > > > > $16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000    
> > > > > > $24: 00000000 00000000                   00000000 00000000 00000000 00000000    
> > > > > > Hi : 00000000                                                                   
> > > > > > Lo : 00000000                                                                   
> > > > > > epc  : 00000000    Not tainted                                                  
> > > > > > Status: 00000000                                                                
> > > > > > Cause : 00000000                                                                
> > > > > > Process sleep (pid: 16, stackpage=87e8c000)                                     
> > > > > 
> > > > > Could you try with the 2.13.1-branch - I believe it should be fine but
> > > > > I haven't tested MIPS in a few merges.
> > > > > 
> > > > 
> > > > I don't have resources to try 2.13.1. The Linux binutils 2.13.90.0.4
> > > > based on 20020814 CVS is ok. I will try to fix CVS.
> > > > 
> > > 
> > > Linker seems ok. It is as which is broken.
> > > 
> > > 
> > > H.J.
> > 
> > Here is the diff. The code looks like
> > 
> > LEAF(mips_atomic_set)
> >         andi    v0, a1, 3               # must be word aligned
> >         bnez    v0, bad_alignment
> > ....
> > LEAF(sys_sysmips)
> >         beq     a0, MIPS_ATOMIC_SET, mips_atomic_set
> >         j       _sys_sysmips
> > END(sys_sysmips)
> > 
> > It is assembled with
> > 
> > # mipsel-linux-gcc -D__ASSEMBLY__ -D__KERNEL__ -I/export/linux/src/kernel/mips/mipsel/include -I /export/linux/src/kernel/mips/mipsel/include/asm/gcc -G 0 -mno-abicalls -fno-pic -pipe -mtune=r4600 -mips2 -Wa,--trap   -c -o scall_o32.o scall_o32.S
> > 
> > My patch:
> > 
> > http://sources.redhat.com/ml/binutils/2002-09/msg00421.html
> > 
> > fixes the Linux kernel. Eric, could you please find a way to fix it?
> > 
> > Thanks.
> > 
> > 
> > H.J.
> > ---
> > 1 2 differ: char 9127, line 328
> > ./arch/mips/kernel/scall_o32.o
> > --- 1	Sun Sep 29 08:28:08 2002
> > +++ 2	Sun Sep 29 08:28:08 2002
> > @@ -325,7 +325,8 @@ Disassembly of section .text:
> >  
> >  0000042c <sys_sysmips>:
> >   42c:	240107d1 	li	at,2001
> > - 430:	1081ffd8 	beq	a0,at,394 <mips_atomic_set>
> > + 430:	10810390 	beq	a0,at,1274 <out+0xd7c>
> > +			430: R_MIPS_PC16	mips_atomic_set
> >   434:	00000000 	nop
> >   438:	08000000 	j	0 <handle_sys>
> >  			438: R_MIPS_26	_sys_sysmips
> > 1 2 differ: char 239806, line 7177
> 
> Alan, I believe your patch
> 
> http://sources.redhat.com/ml/binutils/2002-08/msg00611.html
> 
> doesn't work too well. The problem is the gas relocation is very
> fragile. Any changes to the gas relocation will potentially break
> things. It has been discussed many times before. There are even
> documented in bfd:
> 
> The assembler used @samp{bfd_perform_relocation} for a while.  This
> turned out to be the wrong thing to do, since
> @samp{bfd_perform_relocation} was written to handle relocations on an
> existing object file, while the assembler needed to create relocations
> in a new object file.  The assembler was changed to use the new function
> @samp{bfd_install_relocation} instead, and @samp{bfd_install_relocation}
> was created as a copy of @samp{bfd_perform_relocation}.
> 
> Unfortunately, the work did not progress any farther, so
> @samp{bfd_install_relocation} remains a simple copy of 
> @samp{bfd_perform_relocation}, with all the odd special cases and
> confusing code.  This again is difficult to change, because again any
> change can affect any assembler target, and so is difficult to test.
> 
> In the case of mips, the addend for this file is wrong:
> 
> ---branch-misc-2.s---
> 	.globl g1 .text
> 	.text
> 	.space 20 # <----- Take it out, addend will be fine.
> g1:
> 	.space 20
> x:
> 	bal	g1
> ---
> 
> when compiled with
> 
> # ./as-new -g0 -v -KPIC -o branch-misc-2.o branch-misc-2.s
> 
> If I remembered right, it has something to do with addend added twice.
> Several years ago, I had the pleasure to fix a COFF relocation bug.
> It was ugly. I am afraid your patch may have broken other targets in
> some very strange ways. Could you please look into it?
> 

This patch seems to work for me. I can get a working kernel now. Could
someone please verify it?

Thanks.


H.J.

Attachment: gas-mips.patch
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