Re: [PATCH v2 07/16] riscv: Use generated instruction headers for misaligned loads/stores

[Jesse T]

On Mon, Jun 22, 2026 at 12:08 AM Charlie Jenkins via B4 Relay
<devnull+thecharlesjenkins.gmail.com@xxxxxxxxxx> wrote:
>
> From: Charlie Jenkins <thecharlesjenkins@xxxxxxxxx>
>
> Migrate the misaligned loads/store code to use the generated instruction
> headers instead of the hand-written instruction composition functions.
>
> Signed-off-by: Charlie Jenkins <thecharlesjenkins@xxxxxxxxx>
>
> ---
>
> Similar to the other patches of this series, I extracted out the logic
> of this function and brute forced all possible inputs to validate that
> the outputs are the same. To verify this change in the kernel, I booted
> on Spike and used the misaligned access checker which does some
> misaligned accesses.
> ---
>  arch/riscv/kernel/traps_misaligned.c | 183 ++++++++++++++++-------------------
>  1 file changed, 83 insertions(+), 100 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index 81b7682e6c6d..4d2a2432e0c4 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -22,15 +22,11 @@
>
>  #ifdef CONFIG_FPU
>
> -#define FP_GET_RD(insn)                (insn >> 7 & 0x1F)
> -
>  extern void put_f32_reg(unsigned long fp_reg, unsigned long value);
>
> -static int set_f32_rd(unsigned long insn, struct pt_regs *regs,
> +static int set_f32_rd(unsigned long fp_reg, struct pt_regs *regs,
>                       unsigned long val)
>  {
> -       unsigned long fp_reg = FP_GET_RD(insn);
> -
>         put_f32_reg(fp_reg, val);
>         regs->status |= SR_FS_DIRTY;
>
> @@ -39,9 +35,8 @@ static int set_f32_rd(unsigned long insn, struct pt_regs *regs,
>
>  extern void put_f64_reg(unsigned long fp_reg, unsigned long value);
>
> -static int set_f64_rd(unsigned long insn, struct pt_regs *regs, u64 val)
> +static int set_f64_rd(unsigned long fp_reg, struct pt_regs *regs, u64 val)
>  {
> -       unsigned long fp_reg = FP_GET_RD(insn);
>         unsigned long value;
>
>  #if __riscv_xlen == 32
> @@ -58,10 +53,8 @@ static int set_f64_rd(unsigned long insn, struct pt_regs *regs, u64 val)
>  #if __riscv_xlen == 32
>  extern void get_f64_reg(unsigned long fp_reg, u64 *value);
>
> -static u64 get_f64_rs(unsigned long insn, u8 fp_reg_offset,
> -                     struct pt_regs *regs)
> +static u64 get_f64_rs(unsigned long fp_reg, struct pt_regs *regs)
>  {
> -       unsigned long fp_reg = (insn >> fp_reg_offset) & 0x1F;
>         u64 val;
>
>         get_f64_reg(fp_reg, &val);
> @@ -73,10 +66,8 @@ static u64 get_f64_rs(unsigned long insn, u8 fp_reg_offset,
>
>  extern unsigned long get_f64_reg(unsigned long fp_reg);
>
> -static unsigned long get_f64_rs(unsigned long insn, u8 fp_reg_offset,
> -                               struct pt_regs *regs)
> +static unsigned long get_f64_rs(unsigned long fp_reg, struct pt_regs *regs)
>  {
> -       unsigned long fp_reg = (insn >> fp_reg_offset) & 0x1F;
>         unsigned long val;
>
>         val = get_f64_reg(fp_reg);
> @@ -89,10 +80,8 @@ static unsigned long get_f64_rs(unsigned long insn, u8 fp_reg_offset,
>
>  extern unsigned long get_f32_reg(unsigned long fp_reg);
>
> -static unsigned long get_f32_rs(unsigned long insn, u8 fp_reg_offset,
> -                               struct pt_regs *regs)
> +static unsigned long get_f32_rs(unsigned long fp_reg, struct pt_regs *regs)
>  {
> -       unsigned long fp_reg = (insn >> fp_reg_offset) & 0x1F;
>         unsigned long val;
>
>         val = get_f32_reg(fp_reg);
> @@ -107,28 +96,18 @@ static void set_f32_rd(unsigned long insn, struct pt_regs *regs,
>
>  static void set_f64_rd(unsigned long insn, struct pt_regs *regs, u64 val) {}
>
> -static unsigned long get_f64_rs(unsigned long insn, u8 fp_reg_offset,
> -                               struct pt_regs *regs)
> +static unsigned long get_f64_rs(unsigned long fp_reg, struct pt_regs *regs)
>  {
>         return 0;
>  }
>
> -static unsigned long get_f32_rs(unsigned long insn, u8 fp_reg_offset,
> -                               struct pt_regs *regs)
> +static unsigned long get_f32_rs(unsigned long fp_reg, struct pt_regs *regs)
>  {
>         return 0;
>  }
>
>  #endif
>
> -#define GET_F64_RS2(insn, regs) (get_f64_rs(insn, 20, regs))
> -#define GET_F64_RS2C(insn, regs) (get_f64_rs(insn, 2, regs))
> -#define GET_F64_RS2S(insn, regs) (get_f64_rs(RVC_RS2S(insn), 0, regs))
> -
> -#define GET_F32_RS2(insn, regs) (get_f32_rs(insn, 20, regs))
> -#define GET_F32_RS2C(insn, regs) (get_f32_rs(insn, 2, regs))
> -#define GET_F32_RS2S(insn, regs) (get_f32_rs(RVC_RS2S(insn), 0, regs))
> -
>  #define __read_insn(regs, insn, insn_addr, type)       \
>  ({                                                     \
>         int __ret;                                      \
> @@ -217,13 +196,13 @@ static int handle_vector_misaligned_load(struct pt_regs *regs)
>  }
>  #endif
>
> -static int handle_scalar_misaligned_load(struct pt_regs *regs)
> +static noinline int handle_scalar_misaligned_load(struct pt_regs *regs)
>  {
>         union reg_data val;
>         unsigned long epc = regs->epc;
>         unsigned long insn;
>         unsigned long addr = regs->badaddr;
> -       int fp = 0, shift = 0, len = 0;
> +       int fp = 0, shift = 0, len = 0, rd = 0;
>
>         perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
>
> @@ -240,68 +219,71 @@ static int handle_scalar_misaligned_load(struct pt_regs *regs)
>
>         regs->epc = 0;
>
> -       if ((insn & INSN_MASK_LW) == INSN_MATCH_LW) {
> +       if (riscv_insn_is_lw(insn)) {
>                 len = 4;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -#if defined(CONFIG_64BIT)
> -       } else if ((insn & INSN_MASK_LD) == INSN_MATCH_LD) {
> +               rd = riscv_insn_lw_extract_xd(insn);
> +       } else if (riscv_insn_is_ld(insn)) {
>                 len = 8;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -       } else if ((insn & INSN_MASK_LWU) == INSN_MATCH_LWU) {
> +               rd = riscv_insn_ld_extract_xd(insn);
> +       } else if (riscv_insn_is_lwu(insn)) {
>                 len = 4;
> -#endif
> -       } else if ((insn & INSN_MASK_FLD) == INSN_MATCH_FLD) {
> +               rd = riscv_insn_lwu_extract_xd(insn);
> +       } else if (riscv_insn_is_fld(insn)) {
>                 fp = 1;
>                 len = 8;
> -       } else if ((insn & INSN_MASK_FLW) == INSN_MATCH_FLW) {
> +               rd = riscv_insn_fld_extract_fd(insn);
> +       } else if (riscv_insn_is_flw(insn)) {
>                 fp = 1;
>                 len = 4;
> -       } else if ((insn & INSN_MASK_LH) == INSN_MATCH_LH) {
> +               rd = riscv_insn_flw_extract_fd(insn);
> +       } else if (riscv_insn_is_lh(insn)) {
>                 len = 2;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -       } else if ((insn & INSN_MASK_LHU) == INSN_MATCH_LHU) {
> +               rd = riscv_insn_lh_extract_xd(insn);
> +       } else if (riscv_insn_is_lhu(insn)) {
>                 len = 2;
> -#if defined(CONFIG_64BIT)
> -       } else if ((insn & INSN_MASK_C_LD) == INSN_MATCH_C_LD) {
> +               rd = riscv_insn_lhu_extract_xd(insn);
> +       } else if (riscv_insn_is_c_ld(insn)) {
>                 len = 8;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -               insn = RVC_RS2S(insn) << SH_RD;
> -       } else if ((insn & INSN_MASK_C_LDSP) == INSN_MATCH_C_LDSP &&
> -                  ((insn >> SH_RD) & 0x1f)) {
> +               rd = (8 + riscv_insn_c_ld_extract_xd(insn));
> +       } else if (riscv_insn_is_c_ldsp(insn)) {
>                 len = 8;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -#endif
> -       } else if ((insn & INSN_MASK_C_LW) == INSN_MATCH_C_LW) {
> +               rd = riscv_insn_c_ldsp_extract_xd(insn);
> +       } else if (riscv_insn_is_c_lw(insn)) {
>                 len = 4;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -               insn = RVC_RS2S(insn) << SH_RD;
> -       } else if ((insn & INSN_MASK_C_LWSP) == INSN_MATCH_C_LWSP &&
> -                  ((insn >> SH_RD) & 0x1f)) {
> +               rd = (8 + riscv_insn_c_lw_extract_xd(insn));
> +       } else if (riscv_insn_is_c_lwsp(insn)) {
>                 len = 4;
>                 shift = 8 * (sizeof(unsigned long) - len);
> -       } else if ((insn & INSN_MASK_C_FLD) == INSN_MATCH_C_FLD) {
> +               rd = riscv_insn_c_lwsp_extract_xd(insn);
> +       } else if (riscv_insn_is_c_fld(insn)) {
>                 fp = 1;
>                 len = 8;
> -               insn = RVC_RS2S(insn) << SH_RD;
> -       } else if ((insn & INSN_MASK_C_FLDSP) == INSN_MATCH_C_FLDSP) {
> +               rd = (8 + riscv_insn_c_fld_extract_fd(insn));
> +       } else if (riscv_insn_is_c_fldsp(insn)) {
>                 fp = 1;
>                 len = 8;
> -#if defined(CONFIG_32BIT)
> -       } else if ((insn & INSN_MASK_C_FLW) == INSN_MATCH_C_FLW) {
> +               rd = riscv_insn_c_fldsp_extract_fd(insn);
> +       } else if (riscv_insn_is_c_flw(insn)) {
>                 fp = 1;
>                 len = 4;
> -               insn = RVC_RS2S(insn) << SH_RD;
> -       } else if ((insn & INSN_MASK_C_FLWSP) == INSN_MATCH_C_FLWSP) {
> +               rd = (8 + riscv_insn_c_flw_extract_fd(insn));
> +       } else if (riscv_insn_is_c_flwsp(insn)) {
>                 fp = 1;
>                 len = 4;
> -#endif
> -       } else if ((insn & INSN_MASK_C_LHU) == INSN_MATCH_C_LHU) {
> +               rd = riscv_insn_c_flwsp_extract_fd(insn);
> +       } else if (riscv_insn_is_c_lhu(insn)) {
>                 len = 2;
> -               insn = RVC_RS2S(insn) << SH_RD;
> -       } else if ((insn & INSN_MASK_C_LH) == INSN_MATCH_C_LH) {
> +               rd = (8 + riscv_insn_c_lhu_extract_xd(insn));
> +       } else if (riscv_insn_is_c_lh(insn)) {
>                 len = 2;
> -               shift = 8 * (sizeof(ulong) - len);
> -               insn = RVC_RS2S(insn) << SH_RD;
> +               shift = 8 * (sizeof(unsigned long) - len);
> +               rd = (8 + riscv_insn_c_lh_extract_xd(insn));
>         } else {
>                 regs->epc = epc;
>                 return -1;
> @@ -319,11 +301,11 @@ static int handle_scalar_misaligned_load(struct pt_regs *regs)
>         }
>
>         if (!fp)
> -               SET_RD(insn, regs, (long)(val.data_ulong << shift) >> shift);
> +               *(unsigned long *)((unsigned long *)regs + rd) = val.data_ulong << shift;
>         else if (len == 8)
> -               set_f64_rd(insn, regs, val.data_u64);
> +               set_f64_rd(rd, regs, val.data_u64);
>         else
> -               set_f32_rd(insn, regs, val.data_ulong);
> +               set_f32_rd(rd, regs, val.data_ulong);
>
>         regs->epc = epc + INSN_LEN(insn);
>
> @@ -336,7 +318,7 @@ static int handle_scalar_misaligned_store(struct pt_regs *regs)
>         unsigned long epc = regs->epc;
>         unsigned long insn;
>         unsigned long addr = regs->badaddr;
> -       int len = 0, fp = 0;
> +       int fp = 0, len = 0, rd = 0;
>
>         perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
>
> @@ -351,67 +333,68 @@ static int handle_scalar_misaligned_store(struct pt_regs *regs)
>
>         regs->epc = 0;
>
> -       val.data_ulong = GET_RS2(insn, regs);
> -
> -       if ((insn & INSN_MASK_SW) == INSN_MATCH_SW) {
> +       if (riscv_insn_is_sw(insn)) {
>                 len = 4;
> -#if defined(CONFIG_64BIT)
> -       } else if ((insn & INSN_MASK_SD) == INSN_MATCH_SD) {
> +               rd = riscv_insn_sw_extract_xs2(insn);
> +       } else if (riscv_insn_is_sd(insn)) {
>                 len = 8;
> -#endif
> -       } else if ((insn & INSN_MASK_FSD) == INSN_MATCH_FSD) {
> +               rd = riscv_insn_sd_extract_xs2(insn);
> +       } else if (riscv_insn_is_fsd(insn)) {
>                 fp = 1;
>                 len = 8;
> -               val.data_u64 = GET_F64_RS2(insn, regs);
> -       } else if ((insn & INSN_MASK_FSW) == INSN_MATCH_FSW) {
> +               rd = riscv_insn_fsd_extract_fs2(insn);
> +       } else if (riscv_insn_is_fsw(insn)) {
>                 fp = 1;
>                 len = 4;
> -               val.data_ulong = GET_F32_RS2(insn, regs);
> -       } else if ((insn & INSN_MASK_SH) == INSN_MATCH_SH) {
> +               rd = riscv_insn_fsw_extract_fs2(insn);
> +       } else if (riscv_insn_is_sh(insn)) {
>                 len = 2;
> -#if defined(CONFIG_64BIT)
> -       } else if ((insn & INSN_MASK_C_SD) == INSN_MATCH_C_SD) {
> +               rd = riscv_insn_sh_extract_xs2(insn);
> +       } else if (riscv_insn_is_c_sd(insn)) {
>                 len = 8;
> -               val.data_ulong = GET_RS2S(insn, regs);
> -       } else if ((insn & INSN_MASK_C_SDSP) == INSN_MATCH_C_SDSP) {
> +               rd = riscv_insn_c_sd_extract_xs2(insn);
> +       } else if (riscv_insn_is_c_sdsp(insn)) {
>                 len = 8;
> -               val.data_ulong = GET_RS2C(insn, regs);
> -#endif
> -       } else if ((insn & INSN_MASK_C_SW) == INSN_MATCH_C_SW) {
> +               rd = riscv_insn_c_sdsp_extract_xs2(insn);
> +       } else if (riscv_insn_is_c_sw(insn)) {
>                 len = 4;
> -               val.data_ulong = GET_RS2S(insn, regs);
> -       } else if ((insn & INSN_MASK_C_SWSP) == INSN_MATCH_C_SWSP) {
> +               rd = riscv_insn_c_sw_extract_xs2(insn);
> +       } else if (riscv_insn_is_c_swsp(insn)) {
>                 len = 4;
> -               val.data_ulong = GET_RS2C(insn, regs);
> -       } else if ((insn & INSN_MASK_C_FSD) == INSN_MATCH_C_FSD) {
> +               rd = riscv_insn_c_swsp_extract_xs2(insn);
> +       } else if (riscv_insn_is_c_fsd(insn)) {
>                 fp = 1;
>                 len = 8;
> -               val.data_u64 = GET_F64_RS2S(insn, regs);
> -       } else if ((insn & INSN_MASK_C_FSDSP) == INSN_MATCH_C_FSDSP) {
> +               rd = riscv_insn_c_fsd_extract_fs2(insn);
> +       } else if (riscv_insn_is_c_fsdsp(insn)) {
>                 fp = 1;
>                 len = 8;
> -               val.data_u64 = GET_F64_RS2C(insn, regs);
> -#if !defined(CONFIG_64BIT)

Shouldn't we keep this?

> -       } else if ((insn & INSN_MASK_C_FSW) == INSN_MATCH_C_FSW) {
> +               rd = riscv_insn_c_fsdsp_extract_fs2(insn);
> +       } else if (riscv_insn_is_c_fsw(insn)) {
>                 fp = 1;
>                 len = 4;
> -               val.data_ulong = GET_F32_RS2S(insn, regs);
> -       } else if ((insn & INSN_MASK_C_FSWSP) == INSN_MATCH_C_FSWSP) {
> +               rd = riscv_insn_c_fsw_extract_fs2(insn);
> +       } else if (riscv_insn_is_c_fswsp(insn)) {
>                 fp = 1;
>                 len = 4;
> -               val.data_ulong = GET_F32_RS2C(insn, regs);
> -#endif
> -       } else if ((insn & INSN_MASK_C_SH) == INSN_MATCH_C_SH) {
> +               rd = riscv_insn_c_fswsp_extract_fs2(insn);
> +       } else if (riscv_insn_is_c_sh(insn)) {
>                 len = 2;
> -               val.data_ulong = GET_RS2S(insn, regs);
> +               rd = riscv_insn_c_sh_extract_xs2(insn);
>         } else {
> -               regs->epc = epc;

This line should be kept.

Thanks,
Jesse Taube

>                 return -1;
>         }
>
>         if (!IS_ENABLED(CONFIG_FPU) && fp)
>                 return -EOPNOTSUPP;
>
> +       if (!fp)
> +               val.data_ulong = *(unsigned long *)((unsigned long *)regs + rd);
> +       else if (len == 8)
> +               val.data_u64 = get_f64_rs(rd, regs);
> +       else
> +               val.data_ulong = get_f32_rs(rd, regs);
> +
>         if (user_mode(regs)) {
>                 if (copy_to_user((u8 __user *)addr, &val, len))
>                         return -1;
>
> --
> 2.54.0
>
>
>
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