Re: Why does mips define elf_backend_sign_extend_vma to true?

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

On Tue, Aug 07, 2001 at 08:26:20PM -0700, David B Anderson wrote:
> 
> 
> Andrew Cagney wrote
> |> > Several ABI's have implied sign extension of addresses.  MIPS is one.
> 
>  H . J . Lu wrote
> |> Show me where it is documemnted in the 32bit SVR4 MIPS ABI.
> 
> You have to know where to look :-)
> It's not in the ABI, it's in the hardware.
> When running MIPSIII or MIPSIV.
> The hardware, on loading a 32bit integer value into a 
> 64 bit integer register, sign-extends to 64 bits.
> (for example, with a lw instruction: any 32bit integer
> load does this extension)
> 
> gdb is simply reflecting the hardware action.
> 

What does that have anything to do with ELF files for MIPS I/II? We get
different values on the same 32bit mips ELF file for MIPS I/II:

ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           MIPS R3000
  Version:                           0x1
  Entry point address:               0x8010074c
  Start of program headers:          52 (bytes into file)
  Start of section headers:          2178004 (bytes into file)
  Flags:                             0x10000001, noreorder, mips2 UNKNOWN
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         3
  Size of section headers:           40 (bytes)
  Number of section headers:         18
  Section header string table index: 15

from 32bit bfd and 64bit bfd. I propose this patch to at least fix the
SRV4 ABI. I think the better fix is to check the EF_MIPS field to only
do sign extension for MIPS III/IV. But we don't support such encoding.
I think it is the time to reconsider

http://gcc.gnu.org/ml/gcc-patches/2000-08/msg00418.html

I am willing to provide a patch for that.


H.J.
----
2001-08-07  H.J. Lu  <hjl@gnu.org>

	* elf32-mips.c (elf_backend_sign_extend_vma): Undefine for the
	SVR4 ABI.

Index: elf32-mips.c
===================================================================
RCS file: /work/cvs/gnu/binutils/bfd/elf32-mips.c,v
retrieving revision 1.33
diff -u -p -r1.33 elf32-mips.c
--- elf32-mips.c	2001/07/04 07:34:35	1.33
+++ elf32-mips.c	2001/08/08 04:44:51
@@ -9511,6 +9511,8 @@ static const struct ecoff_debug_swap mip
 
 #define INCLUDED_TARGET_FILE            /* More a type of flag */
 
+#undef elf_backend_sign_extend_vma
+
 #undef TARGET_LITTLE_SYM
 #undef TARGET_LITTLE_NAME
 #undef TARGET_BIG_SYM