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Re: [PATCH] i386: Update -mfunction-return= for return with pop
On Mon, Feb 26, 2018 at 7:06 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> On Mon, Feb 26, 2018 at 2:58 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> >> On Mon, Feb 26, 2018 at 2:05 AM, Martin Liška <mliska@suse.cz> wrote:
>> >> > On 02/25/2018 02:37 AM, H.J. Lu wrote:
>> >> >> PR target/r84530
>> >> >
>> >> > Just a nit I've noticed:
>> >> >
>> >> > s/r84530/84530
>> >>
>> >> Fixed.
>> >>
>> >> --
>> >> H.J.
>> >
>> >> From f08b8721ed038cefcee5a0bb1329b90a2d322269 Mon Sep 17 00:00:00 2001
>> >> From: "H.J. Lu" <hjl.tools@gmail.com>
>> >> Date: Sat, 24 Feb 2018 05:05:49 -0800
>> >> Subject: [PATCH] i386: Update -mfunction-return= for return with pop
>> >>
>> >> When -mfunction-return= is used, simple_return_pop_internal should pop
>> >> return address into ECX register, adjust stack by bytes to pop from stack
>> >> and jump to the return thunk via ECX register.
>> >>
>> >> Tested on i686 and x86-64.
>> >>
>> >> PR target/84530
>> >> * config/i386/i386-protos.h (ix86_output_indirect_jmp): Remove
>> >> the bool argument.
>> >> (ix86_output_indirect_function_return): New prototype.
>> >> (ix86_split_simple_return_pop_internal): Likewise.
>> >> * config/i386/i386.c (indirect_return_via_cx): New.
>> >> (indirect_return_via_cx_bnd): Likewise.
>> >> (indirect_thunk_name): Handle return va CX_REG.
>> >> (output_indirect_thunk_function): Create alias for
>> >> __x86_return_thunk_[re]cx and __x86_return_thunk_[re]cx_bnd.
>> >> (ix86_output_indirect_jmp): Remove the bool argument.
>> >> (ix86_output_indirect_function_return): New function.
>> >> (ix86_split_simple_return_pop_internal): Likewise.
>> >> * config/i386/i386.md (*indirect_jump): Don't pass false
>> >> to ix86_output_indirect_jmp.
>> >> (*tablejump_1): Likewise.
>> >> (simple_return_pop_internal): Change it to define_insn_and_split.
>> >> Call ix86_split_simple_return_pop_internal to split it for
>> >> -mfunction-return=.
>> >> (simple_return_indirect_internal): Call
>> >> ix86_output_indirect_function_return instead of
>> >> ix86_output_indirect_jmp.
>> >
>> > It seems to make sense. Since LLVM has picked up our thunk names now,
>> > I wonder if they have same bug or someohow already assigned a name
>> > to this thunk. In the second case we probably ought to match it. Do
>> > you know what LLVM uses?
>> >
>>
>> I don't think LLVM has implemented -mfunction-return=. I disclosed
>> my -mindirect-branch= approach to LLVM last year. At the time, they
>> wanted freedom in their implementation and didn't want to be compatible
>> with mine. Later they added GCC compatibility so that LLVM may be
>> used to compile Linux kernel. I believe it will be the same case if this
>> option is used to compile Linux kernel.
>
> Patch is OK then, thanks!
>
Checked into trunk. OK for backport to GCC 7 branch after a few days?
--
H.J.