On Fri, Jan 12, 2018 at 9:55 AM, Jan Hubicka <hubi...@ucw.cz> wrote:
>> Add -mfunction-return= option to convert function return to call and
>> return thunks. The default is 'keep', which keeps function return
>> unmodified. 'thunk' converts function return to call and return thunk.
>> 'thunk-inline' converts function return to inlined call and return thunk.
>> 'thunk-extern' converts function return to external call and return
>> thunk provided in a separate object file. You can control this behavior
>> for a specific function by using the function attribute function_return.
>>
>> Function return thunk is the same as memory thunk for -mindirect-branch=
>> where the return address is at the top of the stack:
>>
>> __x86_return_thunk:
>> call L2
>> L1:
>> pause
>> jmp L1
>> L2:
>> lea 8(%rsp), %rsp|lea 4(%esp), %esp
>> ret
>>
>> and function return becomes
>>
>> jmp __x86_return_thunk
>>
>> -mindirect-branch= tests are updated with -mfunction-return=keep to
>> avoid false test failures when -mfunction-return=thunk is added to
>> RUNTESTFLAGS for "make check".
>>
>> gcc/
>>
>> * config/i386/i386-protos.h (ix86_output_function_return): New.
>> * config/i386/i386.c (ix86_set_indirect_branch_type): Also
>> set function_return_type.
>> (indirect_thunk_name): Add ret_p to indicate thunk for function
>> return.
>> (output_indirect_thunk_function): Pass false to
>> indirect_thunk_name.
>> (ix86_output_indirect_branch): Likewise.
>> (output_indirect_thunk_function): Create alias for function
>> return thunk if regno < 0.
>> (ix86_output_function_return): New function.
>> (ix86_handle_fndecl_attribute): Handle function_return.
>> (ix86_attribute_table): Add function_return.
>> * config/i386/i386.h (machine_function): Add
>> function_return_type.
>> * config/i386/i386.md (simple_return_internal): Use
>> ix86_output_function_return.
>> (simple_return_internal_long): Likewise.
>> * config/i386/i386.opt (mfunction-return=): New option.
>> (indirect_branch): Mention -mfunction-return=.
>> * doc/extend.texi: Document function_return function attribute.
>> * doc/invoke.texi: Document -mfunction-return= option.
>>
>> gcc/testsuite/
>>
>> * gcc.target/i386/indirect-thunk-1.c (dg-options): Add
>> -mfunction-return=keep.
>> * gcc.target/i386/indirect-thunk-2.c: Likewise.
>> * gcc.target/i386/indirect-thunk-3.c: Likewise.
>> * gcc.target/i386/indirect-thunk-4.c: Likewise.
>> * gcc.target/i386/indirect-thunk-5.c: Likewise.
>> * gcc.target/i386/indirect-thunk-6.c: Likewise.
>> * gcc.target/i386/indirect-thunk-7.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-1.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-2.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-3.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-4.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-5.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-6.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-7.c: Likewise.
>> * gcc.target/i386/indirect-thunk-attr-8.c: Likewise.
>> * gcc.target/i386/indirect-thunk-bnd-1.c: Likewise.
>> * gcc.target/i386/indirect-thunk-bnd-2.c: Likewise.
>> * gcc.target/i386/indirect-thunk-bnd-3.c: Likewise.
>> * gcc.target/i386/indirect-thunk-bnd-4.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-1.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-2.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-3.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-4.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-5.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-6.c: Likewise.
>> * gcc.target/i386/indirect-thunk-extern-7.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-1.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-2.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-3.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-4.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-5.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-6.c: Likewise.
>> * gcc.target/i386/indirect-thunk-inline-7.c: Likewise.
>> * gcc.target/i386/ret-thunk-1.c: New test.
>> * gcc.target/i386/ret-thunk-10.c: Likewise.
>> * gcc.target/i386/ret-thunk-11.c: Likewise.
>> * gcc.target/i386/ret-thunk-12.c: Likewise.
>> * gcc.target/i386/ret-thunk-13.c: Likewise.
>> * gcc.target/i386/ret-thunk-14.c: Likewise.
>> * gcc.target/i386/ret-thunk-15.c: Likewise.
>> * gcc.target/i386/ret-thunk-16.c: Likewise.
>> * gcc.target/i386/ret-thunk-2.c: Likewise.
>> * gcc.target/i386/ret-thunk-3.c: Likewise.
>> * gcc.target/i386/ret-thunk-4.c: Likewise.
>> * gcc.target/i386/ret-thunk-5.c: Likewise.
>> * gcc.target/i386/ret-thunk-6.c: Likewise.
>> * gcc.target/i386/ret-thunk-7.c: Likewise.
>> * gcc.target/i386/ret-thunk-8.c: Likewise.
>> * gcc.target/i386/ret-thunk-9.c: Likewise.
>>
>> @@ -10846,6 +10888,35 @@ output_indirect_thunk_function (bool need_bnd_p,
>> int regno)
>> ASM_OUTPUT_LABEL (asm_out_file, name);
>> }
>>
>> + if (regno < 0)
>> + {
>> + /* Create alias for __x86.return_thunk/__x86.return_thunk_bnd. */
>> + char alias[32];
>> +
>> + indirect_thunk_name (alias, regno, need_bnd_p, true);
>> + ASM_OUTPUT_DEF (asm_out_file, alias, name);
>> +#if TARGET_MACHO
>> + if (TARGET_MACHO)
>> + {
>> + fputs ("\t.weak_definition\t", asm_out_file);
>> + assemble_name (asm_out_file, alias);
>> + fputs ("\n\t.private_extern\t", asm_out_file);
>> + assemble_name (asm_out_file, alias);
>> + putc ('\n', asm_out_file);
>> + }
>> +#else
>> + if (USE_HIDDEN_LINKONCE)
>> + {
>> + fputs ("\t.globl\t", asm_out_file);
>> + assemble_name (asm_out_file, alias);
>> + putc ('\n', asm_out_file);
>> + fputs ("\t.hidden\t", asm_out_file);
>> + assemble_name (asm_out_file, alias);
>> + putc ('\n', asm_out_file);
>> + }
>> +#endif
>
> Again, I would hope that using generic function output machinery will avoid
> dependency on used assembler here.
I copied it from PIC thunk. We can clean them up for GCC 9.
>> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
>> index 59e5cc8e7e4..7b17773592b 100644
>> --- a/gcc/config/i386/i386.opt
>> +++ b/gcc/config/i386/i386.opt
>> @@ -1026,9 +1026,13 @@ mindirect-branch=
>> Target Report RejectNegative Joined Enum(indirect_branch)
>> Var(ix86_indirect_branch) Init(indirect_branch_keep)
>> Convert indirect call and jump to call and return thunks.
>>
>> +mfunction-return=
>> +Target Report RejectNegative Joined Enum(indirect_branch)
>> Var(ix86_function_return) Init(indirect_branch_keep)
>> +Convert function return to call and return thunk.
>
> I suppose you also want ix86_can_inline_p to check that caller&callee agree
> about thunk usage
> for calls/indirect jumps. For returns we do not care as optimized out return
> is safe?
Thunk usage should be opaque to the rest of compiler.
>>
>> +@item function_return("@var{choice}")
>> +@cindex @code{function_return} function attribute, x86
>> +On x86 targets, the @code{function_return} attribute causes the compiler
>> +to convert function return with @var{choice}. @samp{keep} keeps function
>> +return unmodified. @samp{thunk} converts function return to call and
>> +return thunk. @samp{thunk-inline} converts function return to inlined
>> +call and return thunk. @samp{thunk-extern} converts function return to
>> +external call and return thunk provided in a separate object file.
>
> Again please extend both documentation hunks so it is clear what is purpose
> of this hack.
David, can you help here?
--
H.J.
