Re: [PATCH 2/2] gdb/riscv: Fix buffer overflow on riscv_insn::fetch_instruction

[Tsukasa OI <research_trasio@irq.a4lg.com>]

On 2022/10/04 18:04, Andreas Schwab wrote:
> On Okt 04 2022, Tsukasa OI via Gdb-patches wrote:
> 
>> diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
>> index 47d8f9e601b..99307bd2de1 100644
>> --- a/gdb/riscv-tdep.c
>> +++ b/gdb/riscv-tdep.c
>> @@ -1770,7 +1770,7 @@ riscv_insn::fetch_instruction (struct gdbarch *gdbarch,
>>  			       CORE_ADDR addr, int *len)
>>  {
>>    enum bfd_endian byte_order = gdbarch_byte_order_for_code (gdbarch);
>> -  gdb_byte buf[8];
>> +  gdb_byte buf[22];
> 
> Can the magic number be derived from something else so that is adapts
> automatically?
> 

Well...
That's technically possible but it will make something like...
    8 + 2 + 2 * ((1 << 3) - 1 - 1)
and I don't think that would improve something (it heavily depends on
the encoding magic [no relevant constants are defined so far] so it's
just "from magic to magic").

Defining RISCV_MAX_INSN_LEN might be a slightly better solution (still,
content of RISCV_MAX_INSN_LEN will be a magic number).

Thanks,
Tsukasa