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

[Andrew Burgess]

Pedro Alves <pedro@palves.net> writes:

> 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".

Thanks, I'll work on splitting this patch, and repost.

Andrew


> 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.