[Crash-utility] Re: [PATCH v3 2/5] Call cmd_bt silently after "set pid"

Date: Tue, 3 Jun 2025 17:11:35 +1200 From: Tao Liu <ltao(a)redhat.com&gt; Subject: [Crash-utility] [PATCH v3 2/5] Call cmd_bt silently after "set pid" To: devel(a)lists.crash-utility.osci.io Cc: Alexey Makhalov <alexey.makhalov(a)broadcom.com&gt; Message-ID: <20250603051138.59896-3-ltao(a)redhat.com&gt; Content-Type: text/plain; charset="US-ASCII"; x-default=true Cmd bt will list multi-stacks of one task. After we "set <pid>" switch context to one task, we first need a bt call to detect the multi-stacks, however we don't want any console output from it, so a nullfp is used for output receive. The silent bt call is only triggered once as part of task context switch by cmd set. A array of user_regs pointers is reserved for each supported arch. If one extra stack found, a user_regs structure will be allocated for storing regs value of the stack. Co-developed-by: Alexey Makhalov <alexey.makhalov(a)broadcom.com&gt; Co-developed-by: Tao Liu <ltao(a)redhat.com&gt; Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; --- arm64.c | 4 ++++ crash_target.c | 7 +++++++ kernel.c | 43 +++++++++++++++++++++++++++++++++++++++++++ ppc64.c | 4 ++++ task.c | 4 ++-- x86_64.c | 3 +++ 6 files changed, 63 insertions(+), 2 deletions(-) diff --git a/arm64.c b/arm64.c index 1cdde5f..8291301 100644 --- a/arm64.c +++ b/arm64.c @@ -126,6 +126,10 @@ struct user_regs_bitmap_struct { ulong bitmap[32]; }; +#define MAX_EXCEPTION_STACKS 7 +ulong extra_stacks_idx = 0; +struct user_regs_bitmap_struct *extra_stacks_regs[MAX_EXCEPTION_STACKS] = {0}; + static inline bool is_mte_kvaddr(ulong addr) { /* check for ARM64_MTE enabled */ diff --git a/crash_target.c b/crash_target.c index 71998ef..ad1480c 100644 --- a/crash_target.c +++ b/crash_target.c @@ -31,6 +31,9 @@ extern "C" int crash_get_current_task_reg (int regno, const char *regname, extern "C" int gdb_change_thread_context (void); extern "C" int gdb_add_substack (int); extern "C" void crash_get_current_task_info(unsigned long *pid, char **comm); +#if defined (X86_64) || defined (ARM64) || defined (PPC64) +extern "C" void silent_call_bt(void); +#endif /* The crash target. */ @@ -164,6 +167,10 @@ gdb_change_thread_context (void) /* 3rd, refresh regcache for tid 0 */ target_fetch_registers(get_thread_regcache(inferior_thread()), -1); reinit_frame_cache(); +#if defined (X86_64) || defined (ARM64) || defined (PPC64) + /* 4th, invoke bt silently to refresh the additional stacks */ + silent_call_bt(); +#endif return TRUE; } diff --git a/kernel.c b/kernel.c index b8d3b79..b15c32c 100644 --- a/kernel.c +++ b/kernel.c @@ -12002,3 +12002,46 @@ int get_linux_banner_from_vmlinux(char *buf, size_t size) return TRUE; } + +#if defined(X86_64) || defined(ARM64) || defined(PPC64) +extern ulong extra_stacks_idx; +extern void *extra_stacks_regs[]; +void silent_call_bt(void) +{ + jmp_buf main_loop_env_save; + unsigned long long flags_save = pc->flags; + FILE *fp_save = fp; + FILE *error_fp_save = pc->error_fp; + /* Redirect all cmd_bt() outputs into null */ + fp = pc->nullfp; + pc->error_fp = pc->nullfp; + + for (int i = 0; i < extra_stacks_idx; i++) { + /* Note: GETBUF/FREEBUF is not applicable for extra_stacks_regs, + because we are reserving extra_stacks_regs by cmd_bt() + for later use. But GETBUF/FREEBUF is designed for use only + within one cmd. See process_command_line() -> restore_sanity() + -> free_all_bufs(). So we use malloc/free instead. */ + free(extra_stacks_regs[i]); + extra_stacks_regs[i] = NULL; + } + /* Prepare args used by cmd_bt() */ + sprintf(pc->command_line, "bt\n"); + argcnt = parse_line(pc->command_line, args); + optind = 1; + pc->flags |= RUNTIME;

+ /* Catch error FATAL generated by cmd_bt() if any */ + memcpy(&main_loop_env_save, &pc->main_loop_env, sizeof(jmp_buf)); + if (setjmp(pc->main_loop_env)) { + goto out; + } + cmd_bt(); +out: + /* Restore all */ + memcpy(&pc->main_loop_env, &main_loop_env_save, sizeof(jmp_buf)); + pc->flags = flags_save; + fp = fp_save; + pc->error_fp = error_fp_save; +} +#endif diff --git a/ppc64.c b/ppc64.c index 7ac12fe..532eb3f 100644 --- a/ppc64.c +++ b/ppc64.c @@ -80,6 +80,10 @@ struct user_regs_bitmap_struct { ulong bitmap[32]; }; +#define MAX_EXCEPTION_STACKS 7 +ulong extra_stacks_idx = 0; +struct user_regs_bitmap_struct *extra_stacks_regs[MAX_EXCEPTION_STACKS] = {0}; + static int is_opal_context(ulong sp, ulong nip) { uint64_t opal_start, opal_end; diff --git a/task.c b/task.c index e07b479..ec04b55 100644 --- a/task.c +++ b/task.c @@ -3062,7 +3062,7 @@ sort_context_array(void) curtask = CURRENT_TASK(); qsort((void *)tt->context_array, (size_t)tt->running_tasks, sizeof(struct task_context), sort_by_pid); - set_context(curtask, NO_PID, TRUE); + set_context(curtask, NO_PID, FALSE); sort_context_by_task(); } @@ -3109,7 +3109,7 @@ sort_context_array_by_last_run(void) curtask = CURRENT_TASK(); qsort((void *)tt->context_array, (size_t)tt->running_tasks, sizeof(struct task_context), sort_by_last_run); - set_context(curtask, NO_PID, TRUE); + set_context(curtask, NO_PID, FALSE); sort_context_by_task(); } diff --git a/x86_64.c b/x86_64.c index a46fb9d..ee23d8b 100644 --- a/x86_64.c +++ b/x86_64.c @@ -160,6 +160,9 @@ struct user_regs_bitmap_struct { ulong bitmap[32]; }; +ulong extra_stacks_idx = 0; +struct user_regs_bitmap_struct *extra_stacks_regs[MAX_EXCEPTION_STACKS] = {0}; + /* * Do all necessary machine-specific setup here. This is called several * times during initialization. -- 2.47.0