Re: [Qemu-devel] [PATCH v1 2/2] gdbstub: don't fail on vCont; C04:0; c packets

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

Claudio Imbrenda <imbrenda@linux.vnet.ibm.com> writes:

> On Wed, 31 May 2017 16:09:33 +0100
> Alex Bennée <alex.bennee@linaro.org> wrote:
>
>> The thread-id of 0 means any CPU but we then ignore the fact we find
>> the first_cpu in this case who can have an index of 0. Instead of
>> bailing out just test if we have managed to match up thread-id to a
>> CPU.
>>
>> Otherwise you get:
>>   gdb_handle_packet: command='vCont;C04:0;c'
>>   put_packet: reply='E22'
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> ---
>>  gdbstub.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdbstub.c b/gdbstub.c
>> index a249846954..29c9ed3002 100644
>> --- a/gdbstub.c
>> +++ b/gdbstub.c
>> @@ -934,8 +934,8 @@ static int gdb_handle_vcont(GDBState *s, const
>> char *p)
>>               * CPU first, and only then we can use its index.
>>               */
>>              cpu = find_cpu(idx);
>> -            /* invalid CPU/thread specified */
>> -            if (!idx || !cpu) {
>> +            /* invalid thread specified, cpu not found. */
>> +            if (!cpu) {
>>                  res = -EINVAL;
>>                  goto out;
>>              }
>
> This is strange. cpu_index() is defined as:
>
> static inline int cpu_index(CPUState *cpu)
> {
> #if defined(CONFIG_USER_ONLY)
>     return cpu->host_tid;
> #else
>     return cpu->cpu_index + 1;
> #endif
> }
>
> therefore it shouldn't return 0 under any circumstance, and
> find_cpu(idx) should also fail if idx == 0, because internally it also
> uses cpu_index()
>
> on the other hand, you say that the patch does fix the problem for you,
> which really confuses me.

Hmm that was me assuming cpu_index(cpu) was the same as cpu->cpu_index.
However in the CONFIG_USER_ONLY case we return host_tid which is only
set by clone_func() so I think will not be set for the first cpu.

>
>
>
> (probably) completely unrelatedly, this:
>
> res = qemu_strtoul(p + 1, &p, 16, &tmp);
>
> should be like this instead:
>
> res = qemu_strtoul(p, &p, 16, &tmp);
>
> but this shouldn't impact you in any way.


--
Alex Bennée