[PATCH] x86: Add .nop directive to assembler
Mon Feb 12 19:38:00 GMT 2018
On Mon, Feb 12, 2018 at 7:48 AM, Maciej W. Rozycki <email@example.com> wrote:
> On Mon, 12 Feb 2018, H.J. Lu wrote:
>> My implementation uses the existing relaxation frame work.
>> When we are processing .nop, we don't know exactly how big the
>> the NOP size will be. We allocate a frag with the maximum size
>> and set the exact size after relaxation. After relaxation is done,
>> all frags are converted to rs_fill. We can add rs_fill_nop to
>> support arbitrary .nop directive size. But I don't know if it is
> Right, so this is needed for argument expressions using forward
> references. Understood and accepted. Thank your for patience.
Implement the '.nop SIZE[, LIMIT]' directive for x86 assembler. This
directive emits SIZE bytes filled with 'NOP' instructions. SIZE is
absolute expression, which must be between 0 and 512. LIMIT specifies
the size limit of a single 'NOP' instruction. If the comma and LIMIT
are omitted, LIMIT is assumed to the maximum supported size of a single
'NOP' instruction. The valid values of LIMIT are between 1 and 8 for
16-bit mode, between 1 and 10 for 32-bit mode, between 1 and 11 for
64-bit mode. This directive is only allowed in text sections.
This is implemented by adding a relax state, rs_space_nop, to enum
_relax_state, which is similar to rs_space, but it fills with NOPs,
instead of a single byte. A pseudo relocation, BFD_RELOC_NOP_DIRECTIVE,
is added to fix up frag data with the proper number of NOPs. The new
rs_space_nop state is processed only when TARGET_USE_NOP_DIRECTIVE is
defined. To enable .nop directive, a target backend should
1. Define TARGET_USE_NOP_DIRECTIVE.
2. Create a rs_space_nop frag for .nop directive.
3. Update md_convert_frag to create a fixup with BFD_RELOC_NOP_DIRECTIVE
for rs_space_nop frag.
4. Update md_apply_fix to process fixup with BFD_RELOC_NOP_DIRECTIVE.
OK for master?
Andrew, please test my current users/hjl/nop branch.
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