On 2024/02/08 20:21, Aditya Gupta wrote:
> Hi Kazu,
>
> On Thu, Feb 08, 2024 at 08:40:26AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
>> <...snip...>
>>
>>> Currently, both crash context and gdb's current thread context were
>>> pretty independent, and could be different, for example, crash commands
>>> might be working on thread 6 (CPU 5), but GDB passthroughs will be
>>> working on thread 2 (CPU 1).
>>>
>>> This was not a problem earlier since interaction of crash and gdb was
>>> not depending on current context for most part. But for gdb passthroughs
>>
>>> to work correctly, gdb needs register values from crash, which depend on
>>> current context in crash.
>>
>> Is this true?
>>
>> CURRENT_CONTEXT() is used in ppc64_get_cpu_reg, but get_cpu_reg returns
>> a register value from a cpu, so can't we use get_active_task(cpu) and
>> task_to_context()? if usable, maybe some of the temporary set_cpu()s
>> can be removed.
>
> Nice idea, true, 'get_active_task' can be used instead of me depending
> on CURRENT_CONTEXT.
>
> But, seems everytime 'get_cpu_reg' will be called, 'get_active_task'
> will have to go through all tasks to get the active task. Can I add this
> if condition in 'get_active_task' to optimise it:
It looks like most (all?) dumpfiles should have tt->panic_threads, so
the linear search may not be done with a dumpfile.
if (has_cpu && (tt->flags & POPULATE_PANIC))
tt->panic_threads[tc->processor] = tc->task;
but yes, if there is a slow command, it's good to optimize.
Thanks,
Kazu
>
> --- a/task.c
> +++ b/task.c
> @@ -6308,6 +6308,11 @@ get_active_task(int cpu)
> if (DUMPFILE() && (task = tt->panic_threads[cpu]))
> return task;
>
> + /* return current task if already set to required active task */
> + tc = CURRENT_CONTEXT();
> + if ((tc->processor == cpu) && is_task_active(tc->task))
> + return tc->task;
> +
> tc = FIRST_CONTEXT();
> for (i = 0; i < RUNNING_TASKS(); i++, tc++) {
> if ((tc->processor == cpu) && is_task_active(tc->task))
>
>>
>> The synchronization between crash and gdb is nice for usability, though.
>
> Yes, I think it's better to not remove the set_cpu()s done in
> gdb_refresh_regcache(), so that there are no issues due to the gdb and
> crash contexts not being in sync.
>
>>
>> (it's very helpful if you would rebase the patch set to the latest, when
>> you update this.)
>
> Sure, i will.
>
> Thanks,
> Aditya Gupta
>
>>
>> Thanks,
>> Kazu
>>
>>>
>>> Synchronise 'thread' command in gdb with 'set -c' command in crash.
>>> 1. crash -> gdb synchronisation:
>>> Everytime crash's context changes, a helper is called to switch to
>>> the thread on that CPU in gdb. The function has been implemented in
>>> crash_target.c, since gdb functions are accessible inside
>>> 'crash_target.c', and the thread ID to CPU ID mapping is also done
>>> by the crash_target, during initially registering the threads with
>>> gdb. With this implementation, GDB's default thread initially also
>>> changes to the crashing thread, so a switch to crashing thread
>>> manually isn't required anymore
>>>
>>> 2. gdb -> crash synchronisation:
>>> gdb has been patched to call 'set_cpu' whenever user switches to any
>>> thread.
>>>
>>> Signed-off-by: Aditya Gupta <adityag@xxxxxxxxxxxxx>
>>> ---
>>> crash_target.c | 24 ++++++++++++++++++++++++
>>> defs.h | 3 +++
>>> gdb-10.2.patch | 30 ++++++++++++++++++++++++++++++
>>> kernel.c | 8 +++++++-
>>> task.c | 4 +++-
>>> 5 files changed, 67 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/crash_target.c b/crash_target.c
>>> index 455480679741..a9d7eea8a80e 100644
>>> --- a/crash_target.c
>>> +++ b/crash_target.c
>>> @@ -29,6 +29,8 @@ extern "C" int gdb_readmem_callback(unsigned long, void *, int, int);
>>> extern "C" int crash_get_nr_cpus(void);
>>> extern "C" int crash_get_cpu_reg (int cpu, int regno, const char *regname,
>>> int regsize, void *val);
>>> +extern "C" int gdb_change_cpu_context (unsigned int cpu);
>>> +extern "C" int set_cpu (int cpu);
>>>
>>>
>>> /* The crash target. */
>>> @@ -133,3 +135,25 @@ crash_target_init (void)
>>> /* Now, set up the frame cache. */
>>> reinit_frame_cache ();
>>> }
>>> +
>>> +/*
>>> + * Change gdb's thread context to the thread on given CPU
>>> + **/
>>> +extern "C" int
>>> +gdb_change_cpu_context(unsigned int cpu)
>>> +{
>>> + ptid_t ptid = ptid_t(CRASH_INFERIOR_PID, 0, cpu);
>>> + inferior *inf = current_inferior ();
>>> + thread_info *tp = find_thread_ptid (inf, ptid);
>>> +
>>> + if (tp == nullptr)
>>> + return FALSE;
>>> +
>>> + /* Making sure that crash's context is same */
>>> + set_cpu(cpu);
>>> +
>>> + /* Switch to the thread */
>>> + switch_to_thread(tp);
>>> + return TRUE;
>>> +}
>>> +
>>> diff --git a/defs.h b/defs.h
>>> index 615f3a37935a..7f7a12753658 100644
>>> --- a/defs.h
>>> +++ b/defs.h
>>> @@ -7976,4 +7976,7 @@ enum ppc64_regnum {
>>> PPC64_VRSAVE_REGNU = 139
>>> };
>>>
>>> +/* crash_target.c */
>>> +extern int gdb_change_cpu_context (unsigned int cpu);
>>> +
>>> #endif /* !GDB_COMMON */
>>> diff --git a/gdb-10.2.patch b/gdb-10.2.patch
>>> index 2f7d585105aa..4698079ca343 100644
>>> --- a/gdb-10.2.patch
>>> +++ b/gdb-10.2.patch
>>> @@ -10,6 +10,7 @@
>>>
>>> tar xvzmf gdb-10.2.tar.gz \
>>> gdb-10.2/gdb/symtab.c \
>>> + gdb-10.2/gdb/thread.c \
>>> gdb-10.2/gdb/printcmd.c \
>>> gdb-10.2/gdb/symfile.c \
>>> gdb-10.2/gdb/Makefile.in \
>>> @@ -3237,3 +3238,32 @@ exit 0
>>>
>>> for (compunit_symtab *cust : objfile->compunits ())
>>> {
>>> +--- gdb-10.2/gdb/thread.c.orig
>>> ++++ gdb-10.2/gdb/thread.c
>>> +@@ -58,6 +58,11 @@ static int highest_thread_num;
>>> + /* The current/selected thread. */
>>> + static thread_info *current_thread_;
>>> +
>>> ++#ifdef CRASH_MERGE
>>> ++/* Function to set cpu, defined by crash-utility */
>>> ++extern "C" void set_cpu (int);
>>> ++#endif
>>> ++
>>> + /* RAII type used to increase / decrease the refcount of each thread
>>> + in a given list of threads. */
>>> +
>>> +@@ -1896,7 +1901,13 @@ thread_command (const char *tidstr, int from_tty)
>>> + {
>>> + ptid_t previous_ptid = inferior_ptid;
>>> +
>>> +- thread_select (tidstr, parse_thread_id (tidstr, NULL));
>>> ++ struct thread_info* thread_id = parse_thread_id (tidstr, NULL);
>>> ++
>>> ++#ifdef CRASH_MERGE
>>> ++ set_cpu(thread_id->ptid.tid());
>>> ++#endif
>>> ++
>>> ++ thread_select (tidstr, thread_id);
>>> +
>>> + /* Print if the thread has not changed, otherwise an event will
>>> + be sent. */
>>> diff --git a/kernel.c b/kernel.c
>>> index 52b7ba09f390..a8d60507dd95 100644
>>> --- a/kernel.c
>>> +++ b/kernel.c
>>> @@ -6504,7 +6504,13 @@ set_cpu(int cpu)
>>> if (hide_offline_cpu(cpu))
>>> error(FATAL, "invalid cpu number: cpu %d is OFFLINE\n", cpu);
>>>
>>> - if ((task = get_active_task(cpu)))
>>> + task = get_active_task(cpu);
>>> +
>>> + /* Check if context is already set to given cpu */
>>> + if (task == CURRENT_TASK())
>>> + return;
>>> +
>>> + if (task)
>>> set_context(task, NO_PID);
>>> else
>>> error(FATAL, "cannot determine active task on cpu %ld\n", cpu);
>>> diff --git a/task.c b/task.c
>>> index ebdb5be3786f..3a190cafbacb 100644
>>> --- a/task.c
>>> +++ b/task.c
>>> @@ -5301,7 +5301,9 @@ set_context(ulong task, ulong pid)
>>>
>>> if (found) {
>>> CURRENT_CONTEXT() = tc;
>>> - return TRUE;
>>> +
>>> + /* change the selected thread in gdb, according to current context */
>>> + return gdb_change_cpu_context(tc->processor);
>>> } else {
>>> if (task)
>>> error(INFO, "cannot set context for task: %lx\n", task);
--
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