[PATCH v2] RISC-V: Fix disassembly of partial instructions
Charlie Jenkins
charlie@rivosinc.com
Thu Dec 19 18:37:24 GMT 2024
On Fri, Dec 20, 2024 at 01:37:37AM +0800, Nelson Chu wrote:
> 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.
Oh, I didn't mean to commit that...
>
>
> > 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.
>
Thanks for the formatting info, I will make those changes and send
another version.
- Charlie
>
> > +
> > 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
> >
> >
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