[PATCH RFC v2 riscv/for-next 5/5] riscv: align arch_static_branch function

[Guo Ren]

On Sun, Sep 18, 2022 at 2:39 AM <guoren at kernel.org> wrote:
>
> From: Guo Ren <guoren at linux.alibaba.com>
>
> Reduce size of static branch.
>
> Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren at kernel.org>
> ---
>  arch/riscv/include/asm/jump_label.h | 17 ++++++++++-----
>  arch/riscv/kernel/jump_label.c      | 32 +++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+), 5 deletions(-)
>
> diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
> index 38af2ec7b9bf..78f747dfa8a2 100644
> --- a/arch/riscv/include/asm/jump_label.h
> +++ b/arch/riscv/include/asm/jump_label.h
> @@ -12,17 +12,21 @@
>  #include <linux/types.h>
>  #include <asm/asm.h>
>
> +#ifdef CONFIG_RISCV_ISA_C
> +#define JUMP_LABEL_NOP_SIZE 2
> +#else
>  #define JUMP_LABEL_NOP_SIZE 4
> +#endif
>
>  static __always_inline bool arch_static_branch(struct static_key *key,
>                                                bool branch)
>  {
>         asm_volatile_goto(
> -               "       .option push                            \n\t"
> -               "       .option norelax                         \n\t"
> -               "       .option norvc                           \n\t"
> +#ifdef CONFIG_RISCV_ISA_C
> +               "1:     c.nop                                   \n\t"
> +#else
>                 "1:     nop                                     \n\t"
> -               "       .option pop                             \n\t"
> +#endif
>                 "       .pushsection    __jump_table, \"aw\"    \n\t"
>                 "       .align          " RISCV_LGPTR "         \n\t"
>                 "       .long           1b - ., %l[label] - .   \n\t"
We should check the range during compile time, here. Run-time checking
is the last and most painful method to prevent some errors.

> @@ -39,11 +43,14 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key,
>                                                     bool branch)
>  {
>         asm_volatile_goto(
> +#ifdef CONFIG_RISCV_ISA_C
> +               "1:     c.j             %l[label]               \n\t"
> +#else
>                 "       .option push                            \n\t"
>                 "       .option norelax                         \n\t"
> -               "       .option norvc                           \n\t"
>                 "1:     jal             zero, %l[label]         \n\t"
>                 "       .option pop                             \n\t"
> +#endif
>                 "       .pushsection    __jump_table, \"aw\"    \n\t"
>                 "       .align          " RISCV_LGPTR "         \n\t"
>                 "       .long           1b - ., %l[label] - .   \n\t"
> diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
> index e6694759dbd0..64a4e5df093d 100644
> --- a/arch/riscv/kernel/jump_label.c
> +++ b/arch/riscv/kernel/jump_label.c
> @@ -11,21 +11,52 @@
>  #include <asm/bug.h>
>  #include <asm/patch.h>
>
> +#ifdef CONFIG_RISCV_ISA_C
> +#define RISCV_INSN_C_NOP 0x0001U
> +#define RISCV_INSN_C_JAL 0xa001U
> +#else
>  #define RISCV_INSN_NOP 0x00000013U
>  #define RISCV_INSN_JAL 0x0000006fU
> +#endif
>
>  void arch_jump_label_transform(struct jump_entry *entry,
>                                enum jump_label_type type)
>  {
>         void *addr = (void *)jump_entry_code(entry);
> +#ifdef CONFIG_RISCV_ISA_C
> +       u16 insn;
> +#else
>         u32 insn;
> +#endif
>
>         if (type == JUMP_LABEL_JMP) {
>                 long offset = jump_entry_target(entry) - jump_entry_code(entry);
> +#ifdef CONFIG_RISCV_ISA_C
> +               if (WARN_ON(offset & 1 || offset < -2048 || offset >= 2048))
> +                       return;
>
> +               /*
> +                * 001 | imm[11|4|9:8|10|6|7|3:1|5] 01 - C.JAL
> +                */
> +               insn = RISCV_INSN_C_JAL |
> +                       (((u16)offset & GENMASK(5, 5)) >> (5 - 2)) |
> +                       (((u16)offset & GENMASK(3, 1)) << (3 - 1)) |
> +                       (((u16)offset & GENMASK(7, 7)) >> (7 - 6)) |
> +                       (((u16)offset & GENMASK(6, 6)) << (7 - 6)) |
> +                       (((u16)offset & GENMASK(10, 10)) >> (10 - 8)) |
> +                       (((u16)offset & GENMASK(9, 8)) << (9 - 8)) |
> +                       (((u16)offset & GENMASK(4, 4)) << (11 - 4)) |
> +                       (((u16)offset & GENMASK(11, 11)) << (12 - 11));
> +       } else {
> +               insn = RISCV_INSN_C_NOP;
> +       }
> +#else
>                 if (WARN_ON(offset & 1 || offset < -524288 || offset >= 524288))
For the unify, it also should be:
                   if (WARN_ON(offset & 1 || offset < -2048 || offset >= 2048))

After some tests, 2048 is enough for the current riscv Linux.

>                         return;
>
> +               /*
> +                * imm[20|10:1|11|19:12] | rd | 1101111 - JAL
> +                */
>                 insn = RISCV_INSN_JAL |
>                         (((u32)offset & GENMASK(19, 12)) << (12 - 12)) |
>                         (((u32)offset & GENMASK(11, 11)) << (20 - 11)) |
> @@ -34,6 +65,7 @@ void arch_jump_label_transform(struct jump_entry *entry,
>         } else {
>                 insn = RISCV_INSN_NOP;
>         }
> +#endif
>
>         mutex_lock(&text_mutex);
>         patch_text_nosync(addr, &insn, sizeof(insn));
> --
> 2.36.1
>


-- 
Best Regards
 Guo Ren