[PATCH 03/15] MIPS/GAS: Fix relaxed dword loads/stores

[PATCH 03/15] MIPS/GAS: Fix relaxed dword loads/stores

[Maciej W. Rozycki]

Hi,

 This is a fix for the original issue that made me prepare this series of 
patches.  We have a problem with some doubleword memory access macros such 
as LD.  

 Considering the following program:

$ cat ld.s
	ld	$4,foo+4096

we get the following output:

$ mips-linux-as -32 -o ld.o ld.s
$ mips-linux-objdump -dr ld.o

ld.o:     file format elf32-tradbigmips


Disassembly of section .text:

00000000 <.text>:
   0:	3c010000 	lui	at,0x0
   4:	8c24fffc 	lw	a0,-4(at)
   8:	8c250000 	lw	a1,0(at)
   c:	00000000 	nop

Oops!

 This is fixed by the following change.  It looks like a piece of leftover 
code from old relaxation support has stayed and triggers when a forward 
reference turns out to require absolute addressing.  It also shows how our 
test coverage for these macros is insufficient.  Improving the coverage 
will be the point of the following patches.

2010-10-03  Maciej W. Rozycki  <macro@linux-mips.org>

	gas/
	* config/tc-mips.c (macro)[ldd_std]: Fix the relaxation variant 
	for absolute addressing.

 OK to apply?

  Maciej

binutils-2.20.51-20100925-mips-l-d-reloc.patch
Index: binutils-2.20.51/gas/config/tc-mips.c
===================================================================
--- binutils-2.20.51.orig/gas/config/tc-mips.c
+++ binutils-2.20.51/gas/config/tc-mips.c
@@ -7200,26 +7200,7 @@ macro (struct mips_cl_insn *ip)
 
 	      relax_switch ();
 
-	      /* We just generated two relocs.  When tc_gen_reloc
-		 handles this case, it will skip the first reloc and
-		 handle the second.  The second reloc already has an
-		 extra addend of 4, which we added above.  We must
-		 subtract it out, and then subtract another 4 to make
-		 the first reloc come out right.  The second reloc
-		 will come out right because we are going to add 4 to
-		 offset_expr when we build its instruction below.
-
-		 If we have a symbol, then we don't want to include
-		 the offset, because it will wind up being included
-		 when we generate the reloc.  */
-
-	      if (offset_expr.X_op == O_constant)
-		offset_expr.X_add_number -= 8;
-	      else
-		{
-		  offset_expr.X_add_number = -4;
-		  offset_expr.X_op = O_constant;
-		}
+	      offset_expr.X_add_number -= 4;
 	    }
 	  used_at = 1;
 	  macro_build_lui (&offset_expr, AT);

Re: [PATCH 03/15] MIPS/GAS: Fix relaxed dword loads/stores

[Richard Sandiford]

"Maciej W. Rozycki" <macro@linux-mips.org> writes:
> 2010-10-03  Maciej W. Rozycki  <macro@linux-mips.org>
>
> 	gas/
> 	* config/tc-mips.c (macro)[ldd_std]: Fix the relaxation variant 
> 	for absolute addressing.

OK, thanks.

Richard

Re: [PATCH 03/15] MIPS/GAS: Fix relaxed dword loads/stores

[Maciej W. Rozycki]

On Mon, 4 Oct 2010, Richard Sandiford wrote:

> OK, thanks.

 Committed now, thanks.

  Maciej