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:
--- 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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