On 17/05/22 06:13, Namhyung Kim wrote:
> Hi Adrian,
>
> On Fri, May 13, 2022 at 2:03 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>>
>> A common case for KVM test programs is that the guest object code can be
>> found in the hypervisor process (i.e. the test program running on the
>> host). To support that, copy the host thread's maps to the guest thread's
>> maps. Note, we do not discover the guest until we encounter a guest event,
>> which works well because it is not until then that we know that the host
>> thread's maps have been set up.
>>
>> Typically the main function for the guest object code is called
>> "guest_code", hence the name chosen for this feature.
>
> Ok, so that's just a convention and there's no hard-coded
> support for the "guest_code" function in this code, right?
That is correct.
>
>>
>> This is primarily aimed at supporting Intel PT, or similar, where trace
>> data can be recorded for a guest. Refer to the final patch in this series
>> "perf intel-pt: Add guest_code support" for an example.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>> ---
>> tools/perf/util/event.c | 7 +++-
>> tools/perf/util/machine.c | 70 +++++++++++++++++++++++++++++++++++
>> tools/perf/util/machine.h | 2 +
>> tools/perf/util/session.c | 7 ++++
>> tools/perf/util/symbol_conf.h | 3 +-
>> 5 files changed, 86 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
>> index 6439c888ae38..0476bb3a4188 100644
>> --- a/tools/perf/util/event.c
>> +++ b/tools/perf/util/event.c
>> @@ -683,9 +683,12 @@ static bool check_address_range(struct intlist *addr_list, int addr_range,
>> int machine__resolve(struct machine *machine, struct addr_location *al,
>> struct perf_sample *sample)
>> {
>> - struct thread *thread = machine__findnew_thread(machine, sample->pid,
>> - sample->tid);
>> + struct thread *thread;
>>
>> + if (symbol_conf.guest_code && !machine__is_host(machine))
>> + thread = machine__findnew_guest_code(machine, sample->pid);
>> + else
>> + thread = machine__findnew_thread(machine, sample->pid, sample->tid);
>> if (thread == NULL)
>> return -1;
>>
>> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
>> index e67b5a7670f3..ae2e1fb422e2 100644
>> --- a/tools/perf/util/machine.c
>> +++ b/tools/perf/util/machine.c
>> @@ -392,6 +392,76 @@ struct machine *machines__find_guest(struct machines *machines, pid_t pid)
>> return machine;
>> }
>>
>> +/*
>> + * A common case for KVM test programs is that the guest object code can be
>> + * found in the hypervisor process (i.e. the test program running on the host).
>> + * To support that, copy the host thread's maps to the guest thread's maps.
>> + * Note, we do not discover the guest until we encounter a guest event,
>> + * which works well because it is not until then that we know that the host
>> + * thread's maps have been set up.
>> + */
>> +static struct thread *findnew_guest_code(struct machine *machine,
>
> But this function returns a thread and IIUC that's the task which
> does the host to guest transition. Then why not calling it just
> findnew__hypervisor() ?
The thread returned is in the guest machine. While the code comes
from the hypervisor, it is in the guest VM when it runs.
>From Intel PT point of view, this function allows finding the guest
object code by setting up the guest thread and its maps.
I will try to improve on the explanation in V2.
>
> Thanks,
> Namhyung
>
>
>> + struct machine *host_machine,
>> + pid_t pid)
>> +{
>> + struct thread *host_thread;
>> + struct thread *thread;
>> + int err;
>> +
>> + if (!machine)
>> + return NULL;
>> +
>> + thread = machine__findnew_thread(machine, -1, pid);
>> + if (!thread)
>> + return NULL;
>> +
>> + /* Assume maps are set up if there are any */
>> + if (thread->maps->nr_maps)
>> + return thread;
>> +
>> + host_thread = machine__find_thread(host_machine, -1, pid);
>> + if (!host_thread)
>> + goto out_err;
>> +
>> + thread__set_guest_comm(thread, pid);
>> +
>> + /*
>> + * Guest code can be found in hypervisor process at the same address
>> + * so copy host maps.
>> + */
>> + err = maps__clone(thread, host_thread->maps);
>> + thread__put(host_thread);
>> + if (err)
>> + goto out_err;
>> +
>> + return thread;
>> +
>> +out_err:
>> + thread__zput(thread);
>> + return NULL;
>> +}
>> +
