Re: [PATCH 2/2] lib: sbi: Reduce stack usage of vector misaligned load/store emulation

On Sat, Jun 13, 2026 at 6:51 PM Anup Patel <[email protected]> wrote:
>
> The vector misaligned load/store emulation requires mask[] of 8192
> bytes which cause stack corruptions since default stack size is also
> 8192 bytes.
>
> To address the above issue, allocate mask[] on-demand from heap for
> each hart and store the per-hart pointer in scratch space for reuse.
>
> Signed-off-by: Anup Patel <[email protected]>

This patch is not needed any more due recent improvements in
vector misaligned load/store emulation.

Regards,
Anup

> ---
>  include/sbi/sbi_trap_ldst.h |  2 ++
>  lib/sbi/sbi_trap.c          |  8 +++++
>  lib/sbi/sbi_trap_v_ldst.c   | 61 +++++++++++++++++++++++++++++++++++--
>  3 files changed, 68 insertions(+), 3 deletions(-)
>
> diff --git a/include/sbi/sbi_trap_ldst.h b/include/sbi/sbi_trap_ldst.h
> index a6a6c75b..65539035 100644
> --- a/include/sbi/sbi_trap_ldst.h
> +++ b/include/sbi/sbi_trap_ldst.h
> @@ -37,4 +37,6 @@ int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
>  int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
>                                  struct sbi_trap_context *tcntx);
>
> +int sbi_misaligned_v_ldst_init(void);
> +
>  #endif
> diff --git a/lib/sbi/sbi_trap.c b/lib/sbi/sbi_trap.c
> index 16774fd2..428d9296 100644
> --- a/lib/sbi/sbi_trap.c
> +++ b/lib/sbi/sbi_trap.c
> @@ -459,5 +459,13 @@ static int delegate_traps(struct sbi_scratch *scratch)
>
>  int sbi_trap_init(struct sbi_scratch *scratch, bool cold_boot)
>  {
> +       int rc;
> +
> +       if (cold_boot) {
> +               rc = sbi_misaligned_v_ldst_init();
> +               if (rc)
> +                       return rc;
> +       }
> +
>         return delegate_traps(scratch);
>  }
> diff --git a/lib/sbi/sbi_trap_v_ldst.c b/lib/sbi/sbi_trap_v_ldst.c
> index f4d469dc..e642d4a2 100644
> --- a/lib/sbi/sbi_trap_v_ldst.c
> +++ b/lib/sbi/sbi_trap_v_ldst.c
> @@ -12,15 +12,45 @@
>  #include <sbi/riscv_asm.h>
>  #include <sbi/riscv_encoding.h>
>  #include <sbi/sbi_error.h>
> +#include <sbi/sbi_heap.h>
> +#include <sbi/sbi_scratch.h>
>  #include <sbi/sbi_trap_ldst.h>
>  #include <sbi/sbi_trap.h>
>  #include <sbi/sbi_unpriv.h>
> -#include <sbi/sbi_trap.h>
>
>  #ifdef OPENSBI_CC_SUPPORT_VECTOR
>
>  #define VLEN_MAX 65536
>
> +struct misaligned_v_ldst_data {
> +       uint8_t mask[VLEN_MAX / 8];
> +};
> +
> +static unsigned long misaligned_v_ldst_dataptr_offset;
> +
> +#define misaligned_v_ldst_get_data_ptr(__scratch)                              \
> +       sbi_scratch_read_type((__scratch), void *, misaligned_v_ldst_dataptr_offset)
> +
> +#define misaligned_v_ldst_set_data_ptr(__scratch, __ldst)                      \
> +       sbi_scratch_write_type((__scratch), void *, misaligned_v_ldst_dataptr_offset, (__ldst))
> +
> +static struct misaligned_v_ldst_data *misaligned_v_ldst_thishart_data_ptr(void)
> +{
> +       struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
> +       struct misaligned_v_ldst_data *ptr;
> +
> +       if (!misaligned_v_ldst_dataptr_offset)
> +               return NULL;
> +
> +       ptr = misaligned_v_ldst_get_data_ptr(scratch);
> +       if (!ptr) {
> +               ptr = sbi_zalloc(sizeof(*ptr));
> +               misaligned_v_ldst_set_data_ptr(scratch, ptr);
> +       }
> +
> +       return misaligned_v_ldst_get_data_ptr(sbi_scratch_thishart_ptr());
> +}
> +
>  static inline void set_vreg(ulong vlenb, ulong which,
>                             ulong pos, ulong size, const uint8_t *bytes)
>  {
> @@ -142,6 +172,7 @@ int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
>  {
>         const struct sbi_trap_info *orig_trap = &tcntx->trap;
>         struct sbi_trap_regs *regs = &tcntx->regs;
> +       struct misaligned_v_ldst_data *hart_data;
>         struct sbi_trap_info uptrap;
>         ulong insn = sbi_get_insn(regs->mepc, &uptrap);
>         ulong vl = csr_read(CSR_VL);
> @@ -157,12 +188,17 @@ int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
>         ulong vlmul = GET_VLMUL(vtype);
>         bool illegal = GET_MEW(insn);
>         bool masked = IS_MASKED(insn);
> -       uint8_t mask[VLEN_MAX / 8];
>         uint8_t bytes[8 * sizeof(uint64_t)];
>         ulong len = GET_LEN(view);
>         ulong nf = GET_NF(insn);
>         ulong vemul = GET_VEMUL(vlmul, view, vsew);
>         ulong emul = GET_EMUL(vemul);
> +       uint8_t *mask;
> +
> +       hart_data = misaligned_v_ldst_thishart_data_ptr();
> +       if (!hart_data)
> +               return SBI_ENOMEM;
> +       mask = hart_data->mask;
>
>         if (IS_UNIT_STRIDE_LOAD(insn) || IS_FAULT_ONLY_FIRST_LOAD(insn)) {
>                 stride = nf * len;
> @@ -242,6 +278,7 @@ int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
>  {
>         const struct sbi_trap_info *orig_trap = &tcntx->trap;
>         struct sbi_trap_regs *regs = &tcntx->regs;
> +       struct misaligned_v_ldst_data *hart_data;
>         struct sbi_trap_info uptrap;
>         ulong insn = sbi_get_insn(regs->mepc, &uptrap);
>         ulong vl = csr_read(CSR_VL);
> @@ -257,12 +294,17 @@ int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
>         ulong vlmul = GET_VLMUL(vtype);
>         bool illegal = GET_MEW(insn);
>         bool masked = IS_MASKED(insn);
> -       uint8_t mask[VLEN_MAX / 8];
>         uint8_t bytes[8 * sizeof(uint64_t)];
>         ulong len = GET_LEN(view);
>         ulong nf = GET_NF(insn);
>         ulong vemul = GET_VEMUL(vlmul, view, vsew);
>         ulong emul = GET_EMUL(vemul);
> +       uint8_t *mask;
> +
> +       hart_data = misaligned_v_ldst_thishart_data_ptr();
> +       if (!hart_data)
> +               return SBI_ENOMEM;
> +       mask = hart_data->mask;
>
>         if (IS_UNIT_STRIDE_STORE(insn)) {
>                 stride = nf * len;
> @@ -330,6 +372,15 @@ int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
>
>         return vl;
>  }
> +
> +int sbi_misaligned_v_ldst_init(void)
> +{
> +       misaligned_v_ldst_dataptr_offset = sbi_scratch_alloc_type_offset(void *);
> +       if (!misaligned_v_ldst_dataptr_offset)
> +               return SBI_ENOMEM;
> +
> +       return 0;
> +}
>  #else
>  int sbi_misaligned_v_ld_emulator(int rlen, union sbi_ldst_data *out_val,
>                                  struct sbi_trap_context *tcntx)
> @@ -341,4 +392,8 @@ int sbi_misaligned_v_st_emulator(int wlen, union sbi_ldst_data in_val,
>  {
>         return 0;
>  }
> +int sbi_misaligned_v_ldst_init(void)
> +{
> +       return 0;
> +}
>  #endif /* OPENSBI_CC_SUPPORT_VECTOR */
> --
> 2.43.0
>

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