On Tue, Jan 9, 2018 at 10:55 AM, Jeff Law <l...@redhat.com> wrote:
> On 01/08/2018 03:10 AM, Martin Liška wrote:
>> On 01/07/2018 11:59 PM, H.J. Lu wrote:
>>> +static void
>>> +output_indirect_thunk_function (bool need_bnd_p, int regno)
>>> +{
>>> + char name[32];
>>> + tree decl;
>>> +
>>> + /* Create __x86_indirect_thunk/__x86_indirect_thunk_bnd. */
>>> + indirect_thunk_name (name, regno, need_bnd_p);
>>> + decl = build_decl (BUILTINS_LOCATION, FUNCTION_DECL,
>>> + get_identifier (name),
>>> + build_function_type_list (void_type_node, NULL_TREE));
>>> + DECL_RESULT (decl) = build_decl (BUILTINS_LOCATION, RESULT_DECL,
>>> + NULL_TREE, void_type_node);
>>> + TREE_PUBLIC (decl) = 1;
>>> + TREE_STATIC (decl) = 1;
>>> + DECL_IGNORED_P (decl) = 1;
>>> +
>>> +#if TARGET_MACHO
>>> + if (TARGET_MACHO)
>>> + {
>>> + switch_to_section (darwin_sections[picbase_thunk_section]);
>>> + fputs ("\t.weak_definition\t", asm_out_file);
>>> + assemble_name (asm_out_file, name);
>>> + fputs ("\n\t.private_extern\t", asm_out_file);
>>> + assemble_name (asm_out_file, name);
>>> + putc ('\n', asm_out_file);
>>> + ASM_OUTPUT_LABEL (asm_out_file, name);
>>> + DECL_WEAK (decl) = 1;
>>> + }
>>> + else
>>> +#endif
>>> + if (USE_HIDDEN_LINKONCE)
>>> + {
>>> + cgraph_node::create (decl)->set_comdat_group (DECL_ASSEMBLER_NAME
>>> (decl));
>>> +
>>> + targetm.asm_out.unique_section (decl, 0);
>>> + switch_to_section (get_named_section (decl, NULL, 0));
>>> +
>>> + targetm.asm_out.globalize_label (asm_out_file, name);
>>> + fputs ("\t.hidden\t", asm_out_file);
>>> + assemble_name (asm_out_file, name);
>>> + putc ('\n', asm_out_file);
>>> + ASM_DECLARE_FUNCTION_NAME (asm_out_file, name, decl);
>>> + }
>>> + else
>>> + {
>>> + switch_to_section (text_section);
>>> + ASM_OUTPUT_LABEL (asm_out_file, name);
>>> + }
>>> +
>>> + DECL_INITIAL (decl) = make_node (BLOCK);
>>> + current_function_decl = decl;
>>> + allocate_struct_function (decl, false);
>>> + init_function_start (decl);
>>> + /* We're about to hide the function body from callees of final_* by
>>> + emitting it directly; tell them we're a thunk, if they care. */
>>> + cfun->is_thunk = true;
>>> + first_function_block_is_cold = false;
>>> + /* Make sure unwind info is emitted for the thunk if needed. */
>>> + final_start_function (emit_barrier (), asm_out_file, 1);
>>> +
>>> + output_indirect_thunk (need_bnd_p, regno);
>>> +
>>> + final_end_function ();
>>> + init_insn_lengths ();
>>> + free_after_compilation (cfun);
>>> + set_cfun (NULL);
>>> + current_function_decl = NULL;
>>> +}
>>> +
>>
>> I'm wondering whether thunk creation can be a good target-independent
>> generalization? I guess
>> we can emit the function declaration without direct writes to asm_out_file?
>> And the emission
>> of function body can be potentially a target hook?
>>
>> What about emitting body of the function with RTL instructions instead of
>> direct assembly write?
>> My knowledge of RTL is quite small, but maybe it can bring some
>> generalization and reusability
>> for other targets?
> That's the key point I'm trying to make. We should be looking at
> generalizing this stuff where it makes sense.
>
Thunks are x86 specific and they are created the same way as 32-bit PIC thunks.
I don't see how a target hook is used.
--
H.J.
