Re: [PATCHv3 6/6] gdb: native target invalid architecture detection

[Pedro Alves <pedro@palves.net>]

On 2022-06-30 10:33, Andrew Burgess wrote:
> Pedro Alves <pedro@palves.net> writes:
> 
>> On 2022-06-27 17:27, Andrew Burgess wrote:
>>> Pedro Alves <pedro@palves.net> writes:
>>>> On 2022-06-13 17:15, Andrew Burgess via Gdb-patches wrote:
>>>> I have another question.  I'm confused on how if e.g., on x86-64, you
>>>> load a RISC-V binary into GDB, and the try to run it, we don't end up
>>>> with architecture of the target description instead.
>>>
>>> The problem is that we end up trying to read the registers before we
>>> read the target description.  Which I suspect you will say sounds wrong,
>>> and I agree.
>>>

...

>> Attaching will need some other fix, because in that case, the procedure is that the core
>> requests an attach, and then the target reports an initial stop, and that stop
>> makes infrun read the thread's PC, before setup_inferior is called.  It may be
>> we need to call setup_inferior earlier.  Or maybe we can just add a target_find_description
>> call in linux_nat_target::attach, like remote.c does:
>>
>>  void
>>  extended_remote_target::attach (const char *args, int from_tty)
>>  {
>>  ...
>>    /* Next, if the target can specify a description, read it.  We do
>>       this before anything involving memory or registers.  */
>>    target_find_description ();
>>
>> I haven't looked at that in much detail, and I have to leave for tonight.
> 
> How about the patch below to solve the attach case?

I think this should be two patches.  The part about picking the architecture
of the target isn't specific to attaching.  We're counting on it for "run" too.

>     No test as I don't know how I can reliably compile a binary for a
>     different architecture as part of the testsuite.

We don't even need a binary to trigger badness.  Just need to manually
specify an incompatible architecture, with "set architecture", and then "run".
Like, with current master:

$ gdb -ex "set architecture riscv" ~/gdb/tests/main
GNU gdb (GDB) 13.0.50.20220630-git
...
Reading symbols from /home/pedro/gdb/tests/main...
The target architecture is set to "riscv".
(gdb) r
Starting program: /pedro/gdb/tests/main 
warning: Selected architecture riscv is not compatible with reported target architecture i386:x86-64
warning: Architecture rejected target-supplied description
../../src/gdb/i387-tdep.c:957: internal-error: i387_supply_xsave: Assertion `tdep->st0_regnum >= I386_ST0_REGNUM' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
----- Backtrace -----
0x556325d5365b gdb_internal_backtrace_1
        ../../src/gdb/bt-utils.c:122
0x556325d53714 _Z22gdb_internal_backtracev
        ../../src/gdb/bt-utils.c:168
...

A slight difference here compared to actually having a binary of the wrong arch,
is that this isn't "set architecture auto", so by making choose_architecture_for_target
chose the target architecture, we'd be overriding the explicit user selection.  Maybe
that's OK, not sure.  Maybe the right thing to do in that case (when arch is not auto)
is to error out (and kill/detach the inferior) instead of warning.