linux-kernel - Re: [PATCH v2 3/4] LoongArch: Stop using undocumented assembler options

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Message-ID: <CAAhV-H5nuP2xYREtZuJnq3Sr+JpVbOzLDw+N1ep5yFSUd1+nFQ@mail.gmail.com>
Date:   Thu, 28 Jul 2022 20:25:08 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Xi Ruoyao <xry111@...111.site>
Cc:     loongarch@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Youling Tang <tangyouling@...ngson.cn>,
        Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH v2 3/4] LoongArch: Stop using undocumented assembler options

Hi, Ruoyao,

On Thu, Jul 28, 2022 at 8:03 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> Now we can handle GOT and GOT-based relocations properly, remove the
> undocumented `-Wa,-mla-{global,local}-with-{pcrel,abs}` assembler hacks.
I think "-Wa,-mla-{global,local}-with-{pcrel,abs}" may be regular
options rather than "hacks". If I'm right, the title and commit
message should be updated. And we can send patches to binutils to make
them "documented".

Huacai
>
> And, -fplt is the default of all supported compilers (GCC, and maybe
> Clang in the future), so it can be removed as well.
>
> Adjust assembly code to explicitly use "la.pcrel" where necessary.
>
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> ---
>  arch/loongarch/Makefile      |  4 ----
>  arch/loongarch/kernel/head.S | 10 +++++-----
>  2 files changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 039dcc4fe1f3..800349ea9310 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -40,10 +40,6 @@ endif
>
>  cflags-y                       += -G0 -pipe -msoft-float
>  LDFLAGS_vmlinux                        += -G0 -static -n -nostdlib
> -KBUILD_AFLAGS_KERNEL           += -Wa,-mla-global-with-pcrel
> -KBUILD_CFLAGS_KERNEL           += -Wa,-mla-global-with-pcrel
> -KBUILD_AFLAGS_MODULE           += -Wa,-mla-global-with-abs
> -KBUILD_CFLAGS_MODULE           += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
>
>  cflags-y += -ffreestanding
>  cflags-y += $(call cc-option, -mno-check-zero-division)
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index 74ea7bf6c8d6..193329ed6e8c 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -60,17 +60,17 @@ SYM_CODE_START(kernel_entry)                        # kernel entry point
>         la.abs          t0, 0f
>         jirl            zero, t0, 0
>  0:
> -       la              t0, __bss_start         # clear .bss
> +       la.pcrel        t0, __bss_start         # clear .bss
>         st.d            zero, t0, 0
> -       la              t1, __bss_stop - LONGSIZE
> +       la.pcrel        t1, __bss_stop - LONGSIZE
>  1:
>         addi.d          t0, t0, LONGSIZE
>         st.d            zero, t0, 0
>         bne             t0, t1, 1b
>
> -       la              t0, fw_arg0
> +       la.pcrel        t0, fw_arg0
>         st.d            a0, t0, 0               # firmware arguments
> -       la              t0, fw_arg1
> +       la.pcrel        t0, fw_arg1
>         st.d            a1, t0, 0
>
>         /* KSave3 used for percpu base, initialized as 0 */
> @@ -78,7 +78,7 @@ SYM_CODE_START(kernel_entry)                  # kernel entry point
>         /* GPR21 used for percpu base (runtime), initialized as 0 */
>         or              u0, zero, zero
>
> -       la              tp, init_thread_union
> +       la.pcrel        tp, init_thread_union
>         /* Set the SP after an empty pt_regs.  */
>         PTR_LI          sp, (_THREAD_SIZE - 32 - PT_SIZE)
>         PTR_ADD         sp, sp, tp
> --
> 2.37.0
>
>
>