Re: [PATCH v5 2/2] target/xtensa: Use semihosting/syscalls.h

[Richard Henderson <richard.henderson@linaro.org>]

On 6/28/22 19:08, Max Filippov wrote:
> On Tue, Jun 28, 2022 at 4:43 AM Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> This separates guest file descriptors from host file descriptors,
>> and utilizes shared infrastructure for integration with gdbstub.
>> Remove the xtensa custom console handing and rely on the
>> generic -semihosting-config handling of chardevs.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   target/xtensa/cpu.h         |   1 -
>>   hw/xtensa/sim.c             |   3 -
>>   target/xtensa/xtensa-semi.c | 226 ++++++++----------------------------
>>   3 files changed, 50 insertions(+), 180 deletions(-)
>>
>> diff --git a/target/xtensa/cpu.h b/target/xtensa/cpu.h
>> index ea66895e7f..99ac3efd71 100644
>> --- a/target/xtensa/cpu.h
>> +++ b/target/xtensa/cpu.h
>> @@ -612,7 +612,6 @@ void xtensa_translate_init(void);
>>   void **xtensa_get_regfile_by_name(const char *name, int entries, int bits);
>>   void xtensa_breakpoint_handler(CPUState *cs);
>>   void xtensa_register_core(XtensaConfigList *node);
>> -void xtensa_sim_open_console(Chardev *chr);
>>   void check_interrupts(CPUXtensaState *s);
>>   void xtensa_irq_init(CPUXtensaState *env);
>>   qemu_irq *xtensa_get_extints(CPUXtensaState *env);
>> diff --git a/hw/xtensa/sim.c b/hw/xtensa/sim.c
>> index 946c71cb5b..5cca6a170e 100644
>> --- a/hw/xtensa/sim.c
>> +++ b/hw/xtensa/sim.c
>> @@ -87,9 +87,6 @@ XtensaCPU *xtensa_sim_common_init(MachineState *machine)
>>           xtensa_create_memory_regions(&sysram, "xtensa.sysram",
>>                                        get_system_memory());
>>       }
>> -    if (serial_hd(0)) {
>> -        xtensa_sim_open_console(serial_hd(0));
>> -    }
> 
> I've noticed that with this change '-serial stdio' and its variants are still
> accepted in the command line, but now they do nothing.

Pardon?  They certainly will do something, via writes to the serial hardware.


> This quiet
> change of behavior is unfortunate. I wonder if it would be acceptable
> to map the '-serial stdio' option in the presence of '-semihosting' to
> something like '-chardev stdio,id=id1 -semihosting-config chardev=id1'?

I dunno.  I'm wary of having xtensa be unique here.  Alex, thoughts?

>> +                if (get_user_u32(tv_sec, regs[5]) ||
>> +                    get_user_u32(tv_usec, regs[5])) {
> 
> get_user_u32(tv_usec, regs[5] + 4)?

Oops, yes.

>> -                regs[2] = select(fd + 1,
>> -                                 rq == SELECT_ONE_READ   ? &fdset : NULL,
>> -                                 rq == SELECT_ONE_WRITE  ? &fdset : NULL,
>> -                                 rq == SELECT_ONE_EXCEPT ? &fdset : NULL,
>> -                                 target_tv ? &tv : NULL);
>> -                regs[3] = errno_h2g(errno);
>> +                /* Poll timeout is in milliseconds; overflow to infinity. */
>> +                msec = tv_sec * 1000ull + DIV_ROUND_UP(tv_usec, 1000ull);
>> +                timeout = msec <= INT32_MAX ? msec : -1;
>> +            } else {
>> +                timeout = -1;
>>               }
>> +
>> +            switch (regs[4]) {
>> +            case SELECT_ONE_READ:
>> +                events = G_IO_IN;
>> +                break;
>> +            case SELECT_ONE_WRITE:
>> +                events = G_IO_OUT;
>> +                break;
>> +            case SELECT_ONE_EXCEPT:
>> +                events = G_IO_PRI;
>> +                break;
>> +            default:
>> +                xtensa_cb(cs, -1, EINVAL);
> 
> This doesn't match what there used to be: it was possible to call
> select_one with rq other than SELECT_ONE_* and that would've
> passed NULL for all fd sets in the select invocation turning it into
> a sleep. It would return 0 after the timeout.

Hmm.  Is there any documentation of what it was *supposed* to do?  Passing rq == 
0xdeadbeef and expecting a specific behaviour seems odd.


r~