Re: PATCH: Check invalid x32 relocations.

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Jan 17, 2011 at 6:01 AM, Jan Beulich <JBeulich@novell.com> wrote:
>>>> On 17.01.11 at 13:42, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>> On Mon, Jan 17, 2011 at 1:49 AM, Jan Beulich <JBeulich@novell.com> wrote:
>>>>>> On 15.01.11 at 16:50, "H.J. Lu" <hongjiu.lu@intel.com> wrote:
>>>> --- a/bfd/elf64-x86-64.c
>>>> +++ b/bfd/elf64-x86-64.c
>>>> @@ -1179,6 +1179,39 @@ elf_x86_64_check_relocs (bfd *abfd, struct
>>>> bfd_link_info *info,
>>>> ? ? ? ? ? h = (struct elf_link_hash_entry *) h->root.u.i.link;
>>>> ? ? ? }
>>>>
>>>> + ? ? ?/* Check invalid x32 relocations. ?*/
>>>> + ? ? ?if (!ABI_64_P (abfd))
>>>> + ? ? switch (r_type)
>>>> + ? ? ? {
>>>> + ? ? ? default:
>>>> + ? ? ? ? break;
>>>> +
>>>> + ? ? ? case R_X86_64_64:
>>>
>>> While I buy that all the below ones are meaningless, excluding
>>> the one above seems questionable (and exposes one further
>>> reason why tying the ABI to object file format is bogus). An
>>> obvious use case is to initialize a 64-bit variable with a constant
>>> defined in another object.
>>>
>>
>> Show me how to initialize a 64-bit variable with a constant
>> defined in another object in x32 format in assembly code.
>> I will check it as a testcase.
>
> Source1:
> ? ? ? ?.text
> ? ? ? ?.global _start
> _start:
> ? ? ? ?ret
>
> ? ? ? ?.data
> var: ? ?.quad ? cnst

[hjl@gnu-4 tmp]$ cat x.s
Source1:
       .text
       .global _start
_start:
       ret

       .data
var:    .quad   cnst
[hjl@gnu-4 tmp]$ as --x32 -o x.o x.s
x.s: Assembler messages:
x.s:8: Error: cannot represent relocation type BFD_RELOC_64 in x32 mode
[hjl@gnu-4 tmp]$

> Source2:
> ? ? ? ?.global cnst
> .equ ? ?cnst, 0x12345678

[hjl@gnu-4 tmp]$ cat y.s
       .global cnst
.equ    cnst, 0x123456789abce
[hjl@gnu-4 tmp]$ as --x32 -o y.o y.s
[hjl@gnu-4 tmp]$ nm y.o
6789abce A cnst
[hjl@gnu-4 tmp]$

The problem is cnst can only be 32bit. ".quad cnst" isn't needed.  You can use

     .long cnst
     .long 0

if you really want 64bit value for a 32bit addres.


-- 
H.J.