[PATCH] RISC-V: Avoid updating state until symbol is found

[Nelson Chu]

On Wed, Nov 22, 2023 at 9:35 AM Patrick O'Neill <patrick@rivosinc.com>
wrote:

> Currently objdump gets and updates the map state once per symbol. Updating
> the
> state (partiularly riscv_parse_subset) is expensive and grows quadratically
> since we iterate over all symbols. By deferring this until once we've
> found the
> symbol of interest, we can reduce the time to dump a 4k insn file of
> .norvc and
> .rvc insns from ~47 seconds to ~0.13 seconds.
>
> opcodes/ChangeLog:
>
>         * riscv-dis.c (riscv_get_map_state): Remove state updating logic.
>         (riscv_update_map_state): Add state updating logic to seperate
> function.
>         (riscv_search_mapping_symbol): Use new riscv_update_map_state.
>         (riscv_data_length): Ditto.
>
> Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>
> ---
> Somewhat related to:
>
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=c2f60ac565f1d369fde98146a16f1d3ef79e1000
> Sequences of compressed/uncompressed insns have different isa strings,
> so the cache in that patch is not triggered. Thankfully we can just
> reduce the number of calls to fix this issue rather than create a new
> cache.
> ---
>  opcodes/riscv-dis.c | 47 ++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 38 insertions(+), 9 deletions(-)
>
> diff --git a/opcodes/riscv-dis.c b/opcodes/riscv-dis.c
> index ca328b4c997..4ada1487732 100644
> --- a/opcodes/riscv-dis.c
> +++ b/opcodes/riscv-dis.c
> @@ -860,20 +860,20 @@ riscv_disassemble_insn (bfd_vma memaddr,
>    return insnlen;
>  }
>
> -/* Return true if we find the suitable mapping symbol,
> -   and also update the STATE.  Otherwise, return false.  */
> +/* If we find the suitable mapping symbol update the STATE.
> +   Otherwise, do nothing.  */
>
> -static bool
> -riscv_get_map_state (int n,
> -                    enum riscv_seg_mstate *state,
> -                    struct disassemble_info *info)
> +static void
> +riscv_update_map_state (int n,
> +                       enum riscv_seg_mstate *state,
> +                       struct disassemble_info *info)
>  {
>    const char *name;
>
>    /* If the symbol is in a different section, ignore it.  */
>    if (info->section != NULL
>        && info->section != info->symtab[n]->section)
> -    return false;
> +    return;
>
>    name = bfd_asymbol_name(info->symtab[n]);
>    if (strcmp (name, "$x") == 0)
> @@ -900,10 +900,27 @@ riscv_get_map_state (int n,
>        else
>         riscv_parse_subset (&riscv_rps_dis, name + 2);
>      }
> -  else
> +}
> +
> +/* Return true if we find the suitable mapping symbol.
> +   Otherwise, return false.  */
> +
> +static bool
> +riscv_get_map_state (int n,
> +                    enum riscv_seg_mstate *state,

+                    struct disassemble_info *info)
> +{
> +  const char *name;
> +
> +  /* If the symbol is in a different section, ignore it.  */
> +  if (info->section != NULL
> +      && info->section != info->symtab[n]->section)
>      return false;
>
> -  return true;
> +  name = bfd_asymbol_name(info->symtab[n]);
> +  return (strcmp (name, "$x") == 0
> +         || strcmp (name, "$d") == 0
> +         || strncmp (name, "$xrv", 4) == 0);
>

riscv_elf_is_mapping_symbols?


>  }
>

option 1: remove the unused input *state here, and then maybe change the
function name to riscv_valid_mapping_symbols? or any other names without
"state".
option 2: keep the old riscv_get_map_state, keep updating map_state there,
but don't call riscv_release_subset_list and riscv_parse_subset for
MAP_INSN until riscv_update_map_state (so that we can changed the name to
riscv_update_arch_from_map_state?).


>  /* Check the sorted symbol table (sorted by the symbol value), find the
> @@ -972,6 +989,11 @@ riscv_search_mapping_symbol (bfd_vma memaddr,
>         }
>      }
>
> +  if (found)
> +    riscv_update_map_state (symbol, &mstate, info);
> +  else
> +    riscv_update_map_state (info->symtab_size - 1, &mstate, info);
>

Do we still need to call riscv_update_map_state even if we cannot find any
suitable mapping symbols?


> +
>    /* We can not find the suitable mapping symbol above.  Therefore, we
>       look forwards and try to find it again, but don't go past the start
>       of the section.  Otherwise a data section without mapping symbols
> @@ -996,6 +1018,10 @@ riscv_search_mapping_symbol (bfd_vma memaddr,
>               break;
>             }
>         }
> +      if (found)
> +       riscv_update_map_state (symbol, &mstate, info);
> +      else
> +       riscv_update_map_state (0, &mstate, info);
>

Likewise.


>      }
>
>    if (found)
>

Can we call "riscv_update_map_state (symbol, ...), or
riscv_update_arch_from_map_state" once here?


> @@ -1060,9 +1086,12 @@ riscv_data_length (bfd_vma memaddr,
>               if (addr - memaddr < length)
>                 length = addr - memaddr;
>               found = true;
> +          riscv_update_map_state (n, &m, info);

              break;
>             }
>         }
> +      if (!found)
> +       riscv_update_map_state (0, &m, info);
>

We should already know the map_state is MAP_DATA, and then call into here,
so don't need to update the map_state again?

Thanks
Nelson
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