[PATCH 1/3] RISC-V: build: Pass `-mattr` to `lld`

[twd2]

Hi,

I think we even don't need this option after the issue I filed is fixed.

Thanks!
Wende


On 2021/8/6 4:18, Fāng-ruì Sòng wrote:
> On Thu, Aug 5, 2021 at 1:12 PM twd2 <twd2.me at gmail.com> wrote:
>> Sure. I'll send a v2 after the LLVM issue is resolved.
>>
>> Thanks!
>> Wende
>>
>>
>> On 2021/8/5 4:59, Palmer Dabbelt wrote:
>>> On Mon, 19 Jul 2021 14:14:59 PDT (-0700), ndesaulniers at google.com wrote:
>>>> On Mon, Jul 19, 2021 at 1:53 PM Wende Tan <twd2.me at gmail.com> wrote:
>>>>> Pass `-mattr` to `lld` so that it can generate proper machine code.
>>>>> By the way, it seems that `-march` does not work well now.
>>>>>
>>>>> Signed-off-by: Wende Tan <twd2.me at gmail.com>
>>>>> ---
>>>>>  arch/riscv/Makefile | 7 +++++++
>>>>>  1 file changed, 7 insertions(+)
>>>>>
>>>>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>>>>> index bc74afdbf31e..bbc186a3ab45 100644
>>>>> --- a/arch/riscv/Makefile
>>>>> +++ b/arch/riscv/Makefile
>>>>> @@ -52,9 +52,16 @@ riscv-march-$(CONFIG_ARCH_RV32I)     := rv32ima
>>>>>  riscv-march-$(CONFIG_ARCH_RV64I)       := rv64ima
>>>>>  riscv-march-$(CONFIG_FPU)              := $(riscv-march-y)fd
>>>>>  riscv-march-$(CONFIG_RISCV_ISA_C)      := $(riscv-march-y)c
>>>>> +riscv-mattr-y                          := +m,+a
>>>>> +riscv-mattr-$(CONFIG_FPU)              := $(riscv-mattr-y),+f,+d
>>>>> +riscv-mattr-$(CONFIG_RISCV_ISA_C)      := $(riscv-mattr-y),+c
>>>>>  KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
>>>>>  KBUILD_AFLAGS += -march=$(riscv-march-y)
>>>>>
>>>>> +ifeq ($(CONFIG_LD_IS_LLD),y)
>>>>> +       KBUILD_LDFLAGS += -mllvm -mattr=$(riscv-mattr-y)
>>>> We should prevent the proliferation of the compiler internal `-mllvm`
>>>> flags from Kbuild Makefiles; these are indicative of LLVM IR specific
>>>> issues with regards to LTO.  Can you please file a bug against LLVM
>>>> that `-mattr` should be encoded in the IR for LTO's sake?
>>> Works for me.  I'll hold off on taking this until the LLVM bug gets sorted out and expect a v2 (ideally with the other textual changes Nick suggested).
>>>
>>> Thanks!
> For GNU ld compatibility: -mllvm -mattr=xxx => -plugin-opt=-mattr=xxx
>
> Which can allow us to drop the CONFIG_LD_IS_LLD condition.
> (gold doesn't support RISC-V yet.)
>
> Note: LLVM LTO + GNU ld support is experimental and has very little testing.
> To actually make GNU ld work, we probably also need to teach GNU nm
> and ar to specify --plugin LLVMgold.so
> https://llvm.org/docs/GoldPlugin.html
>
>
>>>> See also:
>>>> commit 0236526d76b8 ("Makefile: lto: Pass -warn-stack-size only on LLD
>>>> < 13.0.0")
>>>> commit 2398ce80152a ("x86, lto: Pass -stack-alignment only on LLD < 13.0.0")
>>>>
>>>>> +endif
>>>>> +
>>>>>  KBUILD_CFLAGS += -mno-save-restore
>>>>>  KBUILD_CFLAGS += -DCONFIG_PAGE_OFFSET=$(CONFIG_PAGE_OFFSET)
>>>>>
>>>>> --
>> --
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>