Re: can target code change architecture setting?

Tim Newsome
2016-10-10T15:39:42Z

That sounds like a good solution. I'll see if I can make it happen.

Thanks, Yao!

Tim

On Mon, Oct 10, 2016 at 2:26 AM, Yao Qi <qiyaoltc@gmail.com> wrote:
> On Fri, Oct 7, 2016 at 6:38 PM, Tim Newsome <tim@sifive.com> wrote:
>> I’m working with riscv gdb support. One problem people occasionally
>> run into is that riscv has both 32- and 64-bit variants. The current
>> gdb code just assumes 64-bit by default (unless a file is specified,
>> and then it gets the info from the ELF info). If such a gdb connects
>> to a 32-bit target, bulk register reads end up wonky, and writes send
>> too much data which confuses OpenOCD. Currently the user needs to do
>> something like set arch riscv:rv32 to work around this.
>>
>> Is it possible for riscv-tdep.c to have some kind of callback function
>> that is called when gdb connects to a server, and for that function to
>> change the register width? If so, gdb could read the riscv misa
>> (instruction set architecture information) register and transparently
>> reconfigure.
>>
>> I looked, but I didn’t see any obvious callbacks that get called when
>> connecting to a target.
>>
>
> I don't know much about riscv, so I assume 32-bit variant and 64-bit
> variant can _not_ co-exist in one program. If so, each variant can
> be abstracted as a gdbarch.
>
> You need to add two target descriptions for 32-bit and 64-bit variants
> respectively, and OpenOCD need to send back the right target
> description to GDB. I assume riscv 32-bit and 64-bit variants have
> different registers.
>
> In GDB side, you need two gdbarch instances, 32-bit riscv and 64-bit
> riscv. In riscv_gdbarch_init, look for the feature from the target
> description (sent by OpenOCD for example), if 32-bit is found, create
> and return gdbarch for 32-bit; if 64-bit is found, create and return
> gdbarch for 64-bit.
>
> If 32-bit variant and 64-bit one is quite different, you even can create
> two tdep.c files, like riscv32-tdep.c and risc64-tdep.c.
>
> --
> Yao (齐尧)