Re: [PATCH] riscv: Use -mno-relax when using lld linker - Fāng-ruì Sòng

From: "Fāng-ruì Sòng" <maskray@google.com>
To: Khem Raj <raj.khem@gmail.com>
Cc: linux-riscv@lists.infradead.org,
	 clang-built-linux <clang-built-linux@googlegroups.com>,
	 Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	 Albert Ou <aou@eecs.berkeley.edu>,
	Nathan Chancellor <nathan@kernel.org>,
	 Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH] riscv: Use -mno-relax when using lld linker
Date: Fri, 14 May 2021 14:14:45 -0700	[thread overview]
Message-ID: <CAFP8O3LH3_EdeCDhJ=tmcgcQdThrQTBvpav3cBWP5Tmqa2OkXA@mail.gmail.com> (raw)
In-Reply-To: <20210514205643.383422-1-raj.khem@gmail.com>

On Fri, May 14, 2021 at 1:57 PM Khem Raj <raj.khem@gmail.com> wrote:
>
> lld does not implement the RISCV relaxation optimizations like GNU ld
> therefore disable it when building with LLVM=1, Also pass it to
> assembler when using external GNU assembler ( LLVM_IAS != 1 ), this
> ensures that relevant assembler option is also enabled along. if these
> options are not used then we see following relocations in objects
>
> 0000000000000000 R_RISCV_ALIGN     *ABS*+0x0000000000000002
>
> These are then rejected by lld
> ld.lld: error: capability.c:(.fixup+0x0): relocation R_RISCV_ALIGN requires unimplemented linker relaxation; recompile with -mno-relax but the .o is already compiled with -mno-relax

This means -mno-relax should emit .option norelax in the assembly.
I'll try fixing this in Clang 13.

> Signed-off-by: Khem Raj <raj.khem@gmail.com>
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> ---
>  arch/riscv/Makefile | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 3eb9590a0775..519f133e0d53 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -38,6 +38,15 @@ else
>         KBUILD_LDFLAGS += -melf32lriscv
>  endif
>
> +ifeq ($(LLVM),1)
> +       KBUILD_CFLAGS += -mno-relax
> +       KBUILD_AFLAGS += -mno-relax
> +ifneq ($(LLVM_IAS),1)
> +       KBUILD_CFLAGS += -Wa,-mno-relax
> +       KBUILD_AFLAGS += -Wa,-mno-relax
> +endif
> +endif
> +
>  # ISA string setting
>  riscv-march-$(CONFIG_ARCH_RV32I)       := rv32ima
>  riscv-march-$(CONFIG_ARCH_RV64I)       := rv64ima
> --
> 2.31.1
>
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-- 
宋方睿

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