Re: [Qemu-devel] [PATCH v2 03/28] semihosting: implement a semihosting console

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Thu, 23 May 2019 at 11:39, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> This provides two functions for handling console output that handle
>> the common backend behaviour for semihosting.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>
>> diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
>> index 08363969c14..b2963547c48 100644
>> --- a/include/exec/gdbstub.h
>> +++ b/include/exec/gdbstub.h
>> @@ -44,6 +44,17 @@ void gdb_do_syscall(gdb_syscall_complete_cb cb, const char *fmt, ...);
>>   * argument list.
>>   */
>>  void gdb_do_syscallv(gdb_syscall_complete_cb cb, const char *fmt, va_list va);
>> +/**
>> + * gdb_do_console_out:
>> + * @gs: guest address of string to send
>> + * @len: length of string
>> + *
>> + * Sends a string to gdb console. Unlike the system call interface
>> + * there is no callback and we assume the system call always
>> + * succeeds.
>> + */
>> +void gdb_do_console_out(target_ulong s, int len);
>
> I'm not sure about the "no callback" part of this API. The operation
> here is genuinely asynchronous and providing no mechanism for the
> caller to be able to say "ok, now wait til it completes" doesn't
> seem like a good plan.

Well the caller doesn't really get a choice. At least in system mode
gdbstub does a vm_stop(RUN_STATE_DEBUG) and brings everything to a halt
anyway. All we've removed is the ability to tack on a callback (which
can get run in all sorts of contexts) when we restart.

I could just drop the API here and allow the semihosting API to call
gdb_do_syscallv directly?

--
Alex Bennée