[Crash-utility] Re: [PATCH v6 3/5] synchronise cpu context changes between crash/gdb

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Hi Kazu,

On Fri, Feb 02, 2024 at 06:41:53AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> On 2024/01/05 16:30, Aditya Gupta wrote:
> > 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.
> > 
> > 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..8c1b43eb07b7 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 \
> > @@ -485,6 +486,35 @@ exit 0
> >    	  return best_pst;
> >          }
> >   
> 
> > +--- 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.  */
> 
> Please move this hunk to the end of gdb-10.2.patch.

Sure, will move this and other hunks mentioned in the reviews.

Thanks,
Aditya Gupta

> 
> Thanks,
> Kazu
> 
> >   --- gdb-10.2/gdb/symfile.c.orig
> >   +++ gdb-10.2/gdb/symfile.c
> >   @@ -652,7 +652,26 @@ default_symfile_offsets (struct objfile *objfile,
> > 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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