[Crash-utility] Re: [PATCH v7 3/5] synchronise cpu context changes between crash/gdb

Hi Kazu, On Thu, Feb 08, 2024 at 08:40:26AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote: 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)) 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. 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(a)linux.ibm.com&gt; > > --- > > 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);