[PATCH,SPU] Add new relocation, R_SPU_ADD_PIC

[Trevor_Smigiel@playstation.sony.com]

Forgot the patch, here it is.

Trevor

* Trevor Smigiel <Trevor_Smigiel@playstation.sony.com> [2009-07-16 15:04]:
> Hi,
> 
> When generating position independent code for Cell SPU, we generate the
> following instruction sequence to compute the address of "symbol":
> 
>     # Compute the base PIC offset
>     ila $2,.+8
>     brsl $3,.+4
>     sf   $126,$2,$3
> 
>     # Add base PIC offset to absolute symbol address
>     ila  $5,symbol
>     a    $5,$5,$126
>     
> When "symbol" is weak and undefined, we want a final value of 0, but the
> above sequence would generate the base PIC offset.
> 
> Also, if DLL's were supported on SPU, we could not simply patch
> relocations at run time and get the correct result.  The DLL loader
> could try subtracting the base PIC offset from symbols when patching,
> but would sometimes end up with a negative number which can not be
> loaded by 1 instruction (that would replace the ila).
> 
> To address both of these issues, we mark the "a" instruction with a
> relocation to indicate that it is adding the base PIC offset to "symbol.
> 
>     # Add base PIC offset to absolute symbol address
>     ila  $5,symbol
>     .reloc .,SPU_ADD_PIC,symbol
>     a    $5,$5,$126
> 
> When the linker see the SPU_ADD_PIC relocation, it checks if "symbol" is
> weak and undefined, or will be dynamically resolved.  If yes, it will
> change the "a" instruction so it becomes a copy instruction.  Thus, the
> value computed in the 'ila' instruction will be correct.  For example,
> change the above "a" to:
> 
>     ai    $5,$5,0  # Add immediate 0
> 
> For this to work the ABI must also specify that it is the third register
> in the 'a' instruction that contains the base PIC offset.
> 
> Currently, binutils does nothing to address these issues.  It just
> generates incorrect values.
> 
> I used an old patch from Alan Modra which had a similar relocation
> called SPU_PIC as a reference and modified his test cases to suit this
> new relocation.
> 
> The attached patch has been tested on SPU and x86 with no new failures.
> 
> Ok?
> 
> Trevor
> 
> 2009-07-10  Trevor Smigiel  <Trevor_Smigiel@playstation.sony.com>
>             Alan Modra  <amodra@bigpond.net.au>
> 
> include/elf/
> 	* spu.h (R_SPU_ADD_PIC): New.
> bfd/
> 	* reloc.c (BFD_RELOC_SPU_ADD_PIC): Define.
> 	* bfd-in2.h: Regenerate.
> 	* libbfd.h: Regenerate.
> 	* elf32-spu.c (elf_howto_table): Add entries SPU_ADD_PIC.
> 	(spu_elf_bfd_to_reloc_type): Handle SPU_ADD_PIC.
> 	(spu_elf_relocate_section): Patch instructions marked by SPU_ADD_PIC.
> gas/
> 	* config/tc-spu.c (md_apply_fix): Handle SPU_ADD_PIC.
> 	* config/tc-spu.h (tc_fix_adjustable): Don't adjust for SPU_ADD_PIC.
> 	(TC_FORCE_RELOCATION): Emit relocs for SPU_ADD_PIC.
> ld/testsuite/
> 	* ld-spu/pic.d: New.
> 	* ld-spu/pic.s: New.
> 	* ld-spu/picdef.s: New.
> 
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