Re: [PATCH 1/1] LoongArch: adjust copy/clear_user exception handler behavior

[WANG Rui]

Hello weihao,

On Wed, Aug 30, 2023 at 9:04 AM liweihao <liweihao@xxxxxxxxxxx> wrote:
>
> The copy/clear_user function should returns number of bytes that could
> not be copied/cleared. So, try to copy/clear byte by byte when ld.d/w/h
> and st.d/w/h trapped into an exception.
>
> Signed-off-by: liweihao <liweihao@xxxxxxxxxxx>
> ---
>  arch/loongarch/lib/clear_user.S |  87 ++++++++---------
>  arch/loongarch/lib/copy_user.S  | 161 ++++++++++++++++----------------
>  2 files changed, 127 insertions(+), 121 deletions(-)
>
> diff --git a/arch/loongarch/lib/clear_user.S b/arch/loongarch/lib/clear_user.S
> index 0790eadce166..9b6eef569f89 100644
> --- a/arch/loongarch/lib/clear_user.S
> +++ b/arch/loongarch/lib/clear_user.S
> @@ -11,19 +11,6 @@
>  #include <asm/cpu.h>
>  #include <asm/regdef.h>
>
> -.irp to, 0, 1, 2, 3, 4, 5, 6, 7
> -.L_fixup_handle_\to\():
> -       sub.d   a0, a2, a0
> -       addi.d  a0, a0, (\to) * (-8)
> -       jr      ra
> -.endr
> -
> -.irp to, 0, 2, 4
> -.L_fixup_handle_s\to\():
> -       addi.d  a0, a1, -\to
> -       jr      ra
> -.endr
> -
>  SYM_FUNC_START(__clear_user)
>         /*
>          * Some CPUs support hardware unaligned access
> @@ -51,7 +38,7 @@ SYM_FUNC_START(__clear_user_generic)
>  2:     move    a0, a1
>         jr      ra
>
> -       _asm_extable 1b, .L_fixup_handle_s0
> +       _asm_extable 1b, 2b
>  SYM_FUNC_END(__clear_user_generic)
>
>  /*
> @@ -173,33 +160,47 @@ SYM_FUNC_START(__clear_user_fast)
>         jr      ra
>
>         /* fixup and ex_table */
> -       _asm_extable 0b, .L_fixup_handle_0
> -       _asm_extable 1b, .L_fixup_handle_0
> -       _asm_extable 2b, .L_fixup_handle_1
> -       _asm_extable 3b, .L_fixup_handle_2
> -       _asm_extable 4b, .L_fixup_handle_3
> -       _asm_extable 5b, .L_fixup_handle_4
> -       _asm_extable 6b, .L_fixup_handle_5
> -       _asm_extable 7b, .L_fixup_handle_6
> -       _asm_extable 8b, .L_fixup_handle_7
> -       _asm_extable 9b, .L_fixup_handle_0
> -       _asm_extable 10b, .L_fixup_handle_1
> -       _asm_extable 11b, .L_fixup_handle_2
> -       _asm_extable 12b, .L_fixup_handle_3
> -       _asm_extable 13b, .L_fixup_handle_0
> -       _asm_extable 14b, .L_fixup_handle_1
> -       _asm_extable 15b, .L_fixup_handle_0
> -       _asm_extable 16b, .L_fixup_handle_0
> -       _asm_extable 17b, .L_fixup_handle_s0
> -       _asm_extable 18b, .L_fixup_handle_s0
> -       _asm_extable 19b, .L_fixup_handle_s0
> -       _asm_extable 20b, .L_fixup_handle_s2
> -       _asm_extable 21b, .L_fixup_handle_s0
> -       _asm_extable 22b, .L_fixup_handle_s0
> -       _asm_extable 23b, .L_fixup_handle_s4
> -       _asm_extable 24b, .L_fixup_handle_s0
> -       _asm_extable 25b, .L_fixup_handle_s4
> -       _asm_extable 26b, .L_fixup_handle_s0
> -       _asm_extable 27b, .L_fixup_handle_s4
> -       _asm_extable 28b, .L_fixup_handle_s0
> +.Llarge_fixup:
> +       sub.d   a1, a2, a0
> +
> +.Lsmall_fixup:
> +29:    st.b    zero, a0, 0
> +       addi.d  a0, a0, 1
> +       addi.d  a1, a1, -1
> +       bgt     a1, zero, 1b

I'm sure the jump target here is 29b.

-- 
WANG Rui