Re: [PATCH v2] RISC-V: Fix disassembly of partial instructions

[Nelson Chu <nelson@rivosinc.com>]

[-- Attachment #1: Type: text/plain, Size: 7179 bytes --]

Some minor GNU coding styles as follows.  Also cc Jan and Andrew, hope they
still have time in their busy schedules can help to see if there are some
side effects.

Thanks
Nelson

On Tue, Dec 17, 2024 at 6:23 AM Charlie Jenkins <charlie@rivosinc.com>
wrote:

> As of commit e43d8768d909 ("RISC-V: Fix disassemble fetch fail return
> value.") partial instructions are no longer disassembled. While that
> commit fixed the behavior of print_insn_riscv() returning the arbitrary
> status value upon failure, it caused the behavior of dumping
> instructions to change. Allow partial instructions to be disassembled
> once again and only return -1 if no part of the instruction was able to
> be disassembled.
>
> Fixes: e43d8768d909 ("RISC-V: Fix disassemble fetch fail return value.")
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
> When testing linux perf, I noticed that this behavior of objdump has
> changed. Before this patch and running `perf test` on riscv the
> following test fails due to objdump not returning all of the expected
> bytes.
>
> Bytes read differ from those read by objdump
> buf1 (dso):
> 0x97 0xf7 0x11 0x00 0x93 0x87 0xc7 0x7c 0x22 0x85 0x7c 0xec 0xef 0x50 0x80
> 0x12
> 0xa6 0x85 0xce 0x86 0x4a 0x86 0x22 0x85 0xef 0x50 0x40 0x40 0xa2 0x84 0x1d
> 0xc9
> 0x7c 0x58 0x85 0x8b 0x85 0xc3 0x1c 0x40 0xa1 0x8b 0x89 0xcf 0x83 0x27 0x04
> 0x0c
> 0x63 0x51 0xf0 0x04 0x97 0xf7 0x11 0x00 0x93 0x87 0x07 0x45 0xbe 0x86 0x58
> 0x70
> 0x74 0xec 0x7c 0xf3 0xa2 0x70 0x02 0x74 0x42 0x69 0xa2 0x69 0x26 0x85 0xe2
> 0x64
> 0x45 0x61 0x82 0x80 0x22 0x85 0xef 0x50 0x50 0x52 0x22 0x85 0xef 0x00 0xb1
> 0x39
> 0xa2 0x70 0x02 0x74 0x81 0x44 0x42 0x69 0xa2 0x69 0x26 0x85 0xe2 0x64 0x45
> 0x61
> 0x82 0x80 0x97 0x06 0x12 0x00 0x93 0x86 0xa6 0x8a 0x97 0xf7 0x11 0x00 0x93
> 0x87
>
> buf2 (objdump):
> 0x97 0xf7 0x11 0x00 0x93 0x87 0xc7 0x7c 0x22 0x85 0x7c 0xec 0xef 0x50 0x80
> 0x12
> 0xa6 0x85 0xce 0x86 0x4a 0x86 0x22 0x85 0xef 0x50 0x40 0x40 0xa2 0x84 0x1d
> 0xc9
> 0x7c 0x58 0x85 0x8b 0x85 0xc3 0x1c 0x40 0xa1 0x8b 0x89 0xcf 0x83 0x27 0x04
> 0x0c
> 0x63 0x51 0xf0 0x04 0x97 0xf7 0x11 0x00 0x93 0x87 0x07 0x45 0xbe 0x86 0x58
> 0x70
> 0x74 0xec 0x7c 0xf3 0xa2 0x70 0x02 0x74 0x42 0x69 0xa2 0x69 0x26 0x85 0xe2
> 0x64
> 0x45 0x61 0x82 0x80 0x22 0x85 0xef 0x50 0x50 0x52 0x22 0x85 0xef 0x00 0xb1
> 0x39
> 0xa2 0x70 0x02 0x74 0x81 0x44 0x42 0x69 0xa2 0x69 0x26 0x85 0xe2 0x64 0x45
> 0x61
> 0x82 0x80 0x97 0x06 0x12 0x00 0x93 0x86 0xa6 0x8a 0x97 0xf7 0x11 0x00 0xad
> 0x00
>
> ---- end(-1) ----
>  24: Object code reading                              : FAILED!
>
> After this patch, this test case no longer fails, as objdump returns the
> expected values.
> ---
> Changes in v2:
> - Fix comment spacing (Jiawei)
> - Link to v1:
> https://lore.kernel.org/r/20241213-fix_objdump_partial_insn-v1-1-7a4963e655d5@rivosinc.com
> ---
>  opcodes/riscv-dis.c | 51
> ++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 46 insertions(+), 5 deletions(-)
>
> diff --git a/opcodes/riscv-dis.c b/opcodes/riscv-dis.c
> index
> 101380f93aafbd528ba0020371f0c43a85f41bd1..492135d4642a29d86757ba0d2ec8261dab66275f
> 100644
> --- a/opcodes/riscv-dis.c
> +++ b/opcodes/riscv-dis.c
> @@ -1308,6 +1308,14 @@ riscv_disassemble_data (bfd_vma memaddr
> ATTRIBUTE_UNUSED,
>        (*info->fprintf_styled_func)
>         (info->stream, dis_style_immediate, "0x%04x", (unsigned) data);
>        break;
> +    case 3:
> +      info->bytes_per_line = 7;
> +      (*info->fprintf_styled_func)
> +       (info->stream, dis_style_assembler_directive, ".word");
> +      (*info->fprintf_styled_func) (info->stream, dis_style_text, "\t");
> +      (*info->fprintf_styled_func)
> +       (info->stream, dis_style_immediate, "0x%06x", (unsigned) data);
> +      break;
>      case 4:
>        info->bytes_per_line = 8;
>        (*info->fprintf_styled_func)
> @@ -1360,13 +1368,28 @@ riscv_init_disasm_info (struct disassemble_info
> *info)
>    return true;
>  }
>
> +/* Fetch an instruction. If only a partial instruction is able to be
> fetched,
> +   return the number of accessible bytes.  */
> +
> +static bfd_vma
> +fetch_insn (bfd_vma memaddr, bfd_byte *packet, bfd_vma dump_size, struct
> disassemble_info *info, volatile int *status)
>

over 80 char per line.


> +{
> +  do
> +    {
> +      *status = (*info->read_memory_func) (memaddr, packet, dump_size,
> info);
> +    }
> +  while(*status != 0 && dump_size-- > 1);
>

Need space between while and left '('


> +
> +  return dump_size;
> +}
> +
>  int
>  print_insn_riscv (bfd_vma memaddr, struct disassemble_info *info)
>  {
>    bfd_byte packet[RISCV_MAX_INSN_LEN];
>    insn_t insn = 0;
> -  bfd_vma dump_size;
> -  int status;
> +  volatile bfd_vma dump_size, bytes_fetched;
> +  volatile int status;
>

Not sure if it needed to be volatile or not.


>    enum riscv_seg_mstate mstate;
>    int (*riscv_disassembler) (bfd_vma, insn_t, const bfd_byte *,
>                              struct disassemble_info *);
> @@ -1398,24 +1421,42 @@ print_insn_riscv (bfd_vma memaddr, struct
> disassemble_info *info)
>    else
>      {
>        /* Get the first 2-bytes to check the lenghth of instruction.  */
> -      status = (*info->read_memory_func) (memaddr, packet, 2, info);
> +      bytes_fetched = fetch_insn(memaddr, packet, 2, info, &status);
>

Need space after the function fetch_insn.


>        if (status != 0)
>         {
>           (*info->memory_error_func) (status, memaddr, info);
>           return -1;
>         }
> +      else if (bytes_fetched != 2)
> +       {
> +         /* Only the first byte was able to be read. Dump the partial
> +            instruction.  */
>

Two spaces after '.'


> +         dump_size = bytes_fetched;
> +         info->bytes_per_chunk = dump_size;
> +         riscv_disassembler = riscv_disassemble_data;
> +        goto print;
>

Indent, seems to miss a space.


> +       }
>        insn = (insn_t) bfd_getl16 (packet);
>        dump_size = riscv_insn_length (insn);
>        riscv_disassembler = riscv_disassemble_insn;
>      }
>
> -  /* Fetch the instruction to dump.  */
> -  status = (*info->read_memory_func) (memaddr, packet, dump_size, info);
> +  bytes_fetched = fetch_insn(memaddr, packet, dump_size, info, &status);
>

Need space after the function fetch_insn.


> +
>    if (status != 0)
>      {
>        (*info->memory_error_func) (status, memaddr, info);
>        return -1;
>      }
> +  else if (bytes_fetched != dump_size)
> +    {
> +      dump_size = bytes_fetched;
> +      info->bytes_per_chunk = dump_size;
> +      riscv_disassembler = riscv_disassemble_data;
> +    }
> +
> +print:
>

Indent, one space needed for the label.


> +
>    insn = (insn_t) bfd_get_bits (packet, dump_size * 8, false);
>
>    return (*riscv_disassembler) (memaddr, insn, packet, info);
>
> ---
> base-commit: 978324718990b6b371d4eeeba02cfe13a0ebf120
> change-id: 20241121-fix_objdump_partial_insn-94e236f3db38
> --
> - Charlie
>
>

[-- Attachment #2: Type: text/html, Size: 9646 bytes --]