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

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.

[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 > > --