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

From: twd2 <twd2.me@gmail.com>
To: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	aou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
	clang-built-linux@googlegroups.com, masahiroy@kernel.org,
	keescook@chromium.org, Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH 1/3] RISC-V: build: Pass `-mattr` to `lld`
Date: Fri, 6 Aug 2021 04:12:41 +0800	[thread overview]
Message-ID: <a6615b69-d99f-220b-d980-1f5f40ee2999@gmail.com> (raw)
In-Reply-To: <mhng-4af8be52-7620-478b-bf69-73306a2ffc3b@palmerdabbelt-glaptop>

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@google.com wrote:
>> On Mon, Jul 19, 2021 at 1:53 PM Wende Tan <twd2.me@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@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!
>
>>
>> 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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