On Thu, Jan 11, 2018 at 2:54 PM, Jeff Law <l...@redhat.com> wrote: > On 01/07/2018 03:59 PM, H.J. Lu 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: >> lfence >> 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=lfence 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. > Same high level comments apply here. ie, expecting Uros to chime in and > thus final approval rests with Uros. Is there significant value in > having return thunks in the object file?
To better support -mindirect-branch-loop= if it is ever needed. > Is this something that is currently used or requested by the kernel teams? Yes, it is requested by the kernel teams? >> @@ -28539,6 +28610,43 @@ ix86_output_indirect_jmp (rtx call_op, bool ret_p) >> return "%!jmp\t%A0"; >> } >> >> +const char * >> +ix86_output_function_return (bool long_p) > Needs function comment. Will do. > >> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt >> index f3e43da0aed..2b62363973d 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. >> >> +mfunction-return= >> +Target Report RejectNegative Joined Enum(indirect_branch) >> Var(ix86_function_return) Init(indirect_branch_keep) >> +Convert function return. > Again, reads poorly. > Will update. -- H.J.
