[Crash-utility] Re: [PATCH v3 5/5] ppc64: Add gdb multi-stack unwind support

On Thu, Jun 19, 2025 at 7:16 PM Tao Liu <ltao(a)redhat.com&gt; wrote: > > Hi lianbo, > > On Thu, Jun 19, 2025 at 2:49 PM lijiang <lijiang(a)redhat.com&gt; wrote: > > > > For ppc64 machine, I noticed that the gdb bt may not work as expected, for example: > > > > crash> set 2 > > PID: 2 > > COMMAND: "kthreadd" > > TASK: c000000004797f80 [THREAD_INFO: c000000004797f80] > > CPU: 0 > > STATE: TASK_INTERRUPTIBLE > > crash> bt > > PID: 2 TASK: c000000004797f80 CPU: 0 COMMAND: "kthreadd" > > #0 [c00000000484fbc0] _end at c00000000484fd70 (unreliable) > > #1 [c00000000484fd70] __switch_to at c00000000001fabc > > #2 [c00000000484fdd0] __schedule at c0000000011ca9dc > > #3 [c00000000484feb0] schedule at c0000000011caeb0 > > #4 [c00000000484ff20] kthreadd at c0000000001af6c4 > > #5 [c00000000484ffe0] start_kernel_thread at c00000000000ded8 > > crash> gdb bt > > #0 0xc00000000484fd70 in ?? () > > gdb: gdb request failed: bt > > crash> > > crash> sys|grep RELEASE > > RELEASE: 6.12.0 > > > > Is that expected behavior?(I do not remember if I mentioned the similar issue in the previous patch review.) > > > This is a ppc bug which we encountered some time ago. See [1], in > short, we cannot determine ABI_V2/V1 correctly, a ABI_V2 kernel might > running a ABI_V1 program, see [2]. But it has no relation to gdb bt. > Can you also add it to the patch log? At least we can mark it as a known issue, and it's easy to recall this case in the future.

Thanks Lianbo > > [1]: https://www.mail-archive.com/devel@lists.crash-utility.osci.io/msg01124.html > [2]: https://www.mail-archive.com/devel@lists.crash-utility.osci.io/msg01139.html > > > I have no more comments for other changes, just three issues(see another two comments). > > Thanks, > Tao Liu > > > > > Thanks > > Lianbo > > > > On Tue, Jun 3, 2025 at 1:18 PM <devel-request(a)lists.crash-utility.osci.io&gt; wrote: > >> > >> Date: Tue, 3 Jun 2025 17:11:38 +1200 > >> From: Tao Liu <ltao(a)redhat.com&gt; > >> Subject: [Crash-utility] [PATCH v3 5/5] ppc64: Add gdb multi-stack > >> unwind support > >> To: devel(a)lists.crash-utility.osci.io > >> Cc: Alexey Makhalov <alexey.makhalov(a)broadcom.com&gt; > >> Message-ID: <20250603051138.59896-6-ltao(a)redhat.com&gt; > >> Content-Type: text/plain; charset="US-ASCII"; x-default=true > >> > >> 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; > >> --- > >> ppc64.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++----- > >> 1 file changed, 64 insertions(+), 6 deletions(-) > >> > >> diff --git a/ppc64.c b/ppc64.c > >> index 532eb3f..d1a5067 100644 > >> --- a/ppc64.c > >> +++ b/ppc64.c > >> @@ -2053,6 +2053,7 @@ ppc64_back_trace_cmd(struct bt_info *bt) > >> char buf[BUFSIZE]; > >> struct gnu_request *req; > >> extern void print_stack_text_syms(struct bt_info *, ulong, ulong); > >> + extra_stacks_idx = 0; > >> > >> bt->flags |= BT_EXCEPTION_FRAME; > >> > >> @@ -2071,6 +2072,29 @@ ppc64_back_trace_cmd(struct bt_info *bt) > >> req->pc = bt->instptr; > >> req->sp = bt->stkptr; > >> > >> + if (is_task_active(bt->task)) { > >> + if (!extra_stacks_regs[extra_stacks_idx]) { > >> + extra_stacks_regs[extra_stacks_idx] = > >> + (struct user_regs_bitmap_struct *) > >> + malloc(sizeof(struct user_regs_bitmap_struct)); > >> + } > >> + memset(extra_stacks_regs[extra_stacks_idx], 0, > >> + sizeof(struct user_regs_bitmap_struct)); > >> + extra_stacks_regs[extra_stacks_idx]->ur.nip = req->pc; > >> + extra_stacks_regs[extra_stacks_idx]->ur.gpr[1] = req->sp; > >> + SET_BIT(extra_stacks_regs[extra_stacks_idx]->bitmap, > >> + REG_SEQ(ppc64_pt_regs, nip)); > >> + SET_BIT(extra_stacks_regs[extra_stacks_idx]->bitmap, > >> + REG_SEQ(ppc64_pt_regs, gpr[0]) + 1); > >> + if (!bt->machdep || > >> + (extra_stacks_regs[extra_stacks_idx]->ur.gpr[1] != > >> + ((struct user_regs_bitmap_struct *)(bt->machdep))->ur.gpr[1] && > >> + extra_stacks_regs[extra_stacks_idx]->ur.nip != > >> + ((struct user_regs_bitmap_struct *)(bt->machdep))->ur.nip)) { > >> + gdb_add_substack (extra_stacks_idx++); > >> + } > >> + } > >> + > >> if (bt->flags & > >> (BT_TEXT_SYMBOLS|BT_TEXT_SYMBOLS_PRINT|BT_TEXT_SYMBOLS_NOPRINT)) { > >> if (!INSTACK(req->sp, bt)) > >> @@ -2512,6 +2536,28 @@ ppc64_print_eframe(char *efrm_str, struct ppc64_pt_regs *regs, > >> fprintf(fp, " %s [%lx] exception frame:\n", efrm_str, regs->trap); > >> ppc64_print_regs(regs); > >> ppc64_print_nip_lr(regs, 1); > >> + > >> + if (!((regs->msr >> MSR_PR_LG) & 0x1) && > >> + !(bt->flags & BT_EFRAME_SEARCH)) { > >> + if (!extra_stacks_regs[extra_stacks_idx]) { > >> + extra_stacks_regs[extra_stacks_idx] = > >> + (struct user_regs_bitmap_struct *) > >> + malloc(sizeof(struct user_regs_bitmap_struct)); > >> + } > >> + memset(extra_stacks_regs[extra_stacks_idx], 0, > >> + sizeof(struct user_regs_bitmap_struct)); > >> + memcpy(&extra_stacks_regs[extra_stacks_idx]->ur, regs, > >> + sizeof(struct ppc64_pt_regs)); > >> + for (int i = 0; i < sizeof(struct ppc64_pt_regs)/sizeof(ulong); i++) > >> + SET_BIT(extra_stacks_regs[extra_stacks_idx]->bitmap, i); > >> + if (!bt->machdep || > >> + (extra_stacks_regs[extra_stacks_idx]->ur.gpr[1] != > >> + ((struct user_regs_bitmap_struct *)(bt->machdep))->ur.gpr[1] && > >> + extra_stacks_regs[extra_stacks_idx]->ur.nip != > >> + ((struct user_regs_bitmap_struct *)(bt->machdep))->ur.nip)) { > >> + gdb_add_substack (extra_stacks_idx++); > >> + } > >> + } > >> } > >> > >> static int > >> @@ -2552,6 +2598,12 @@ ppc64_get_current_task_reg(int regno, const char *name, int size, > >> tc = CURRENT_CONTEXT(); > >> if (!tc) > >> return FALSE; > >> + > >> + if (sid && sid <= extra_stacks_idx) { > >> + ur_bitmap = extra_stacks_regs[sid - 1]; > >> + goto get_sub; > >> + } > >> + > >> BZERO(&bt_setup, sizeof(struct bt_info)); > >> clone_bt_info(&bt_setup, &bt_info, tc); > >> fill_stackbuf(&bt_info); > >> @@ -2570,39 +2622,45 @@ ppc64_get_current_task_reg(int regno, const char *name, int size, > >> goto get_all; > >> } > >> > >> +get_sub: > >> switch (regno) { > >> case PPC64_R0_REGNUM ... PPC64_R31_REGNUM: > >> if (!NUM_IN_BITMAP(ur_bitmap->bitmap, > >> REG_SEQ(ppc64_pt_regs, gpr[0]) + regno - PPC64_R0_REGNUM)) { > >> - FREEBUF(ur_bitmap); > >> + if (!sid) > >> + FREEBUF(ur_bitmap); > >> return FALSE; > >> } > >> break; > >> case PPC64_PC_REGNUM: > >> if (!NUM_IN_BITMAP(ur_bitmap->bitmap, > >> REG_SEQ(ppc64_pt_regs, nip))) { > >> - FREEBUF(ur_bitmap); > >> + if (!sid) > >> + FREEBUF(ur_bitmap); > >> return FALSE; > >> } > >> break; > >> case PPC64_MSR_REGNUM: > >> if (!NUM_IN_BITMAP(ur_bitmap->bitmap, > >> REG_SEQ(ppc64_pt_regs, msr))) { > >> - FREEBUF(ur_bitmap); > >> + if (!sid) > >> + FREEBUF(ur_bitmap); > >> return FALSE; > >> } > >> break; > >> case PPC64_LR_REGNUM: > >> if (!NUM_IN_BITMAP(ur_bitmap->bitmap, > >> REG_SEQ(ppc64_pt_regs, link))) { > >> - FREEBUF(ur_bitmap); > >> + if (!sid) > >> + FREEBUF(ur_bitmap); > >> return FALSE; > >> } > >> break; > >> case PPC64_CTR_REGNUM: > >> if (!NUM_IN_BITMAP(ur_bitmap->bitmap, > >> REG_SEQ(ppc64_pt_regs, ctr))) { > >> - FREEBUF(ur_bitmap); > >> + if (!sid) > >> + FREEBUF(ur_bitmap); > >> return FALSE; > >> } > >> break; > >> @@ -2645,7 +2703,7 @@ get_all: > >> ret = TRUE; > >> break; > >> } > >> - if (bt_info.need_free) { > >> + if (!sid && bt_info.need_free) { > >> FREEBUF(ur_bitmap); > >> bt_info.need_free = FALSE; > >> } > >> -- > >> 2.47.0 > > > > -- >