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

[Nick Desaulniers]

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?

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)
>
> --


--
Thanks,
~Nick Desaulniers