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Re: PATCH: Check invalid x32 relocations.
>>> On 17.01.11 at 15:13, "H.J. Lu" <hjl.tools@gmail.com> wrote:
> 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
That is what I was complaining about,
> [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
..., while that is because you force use of 32-bit ELF. And it
certainly seems bogus that there's not even a warning.
> [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.
If I control the directive, I could do so. If, however, the directive
gets produced by a compiler, I can't (and depend on either the
compiler doing the conversion for me, or a suitable relocation to
be available).
Jan