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

[Palmer Dabbelt]

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!

>
> 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)
>>
>> --