[Crash-utility] Re: [PATCH] ppc64: Fix bt printing error stack trace

A error stack trace of bt cmd observed: crash> bt 1 PID: 1 TASK: c000000003714b80 CPU: 2 COMMAND: "systemd" #0 [c0000000037735c0] _end at c0000000037154b0 (unreliable) #1 [c000000003773770] __switch_to at c00000000001fa9c #2 [c0000000037737d0] __schedule at c00000000112e4ec #3 [c0000000037738b0] schedule at c00000000112ea80 ... The #0 stack trace is incorrect, the function address shouldn't exceed _end. The reason is for kernel>=v6.2, the offset of pt_regs to sp changed from STACK_FRAME_OVERHEAD, i.e 112, to STACK_SWITCH_FRAME_REGS. For CONFIG_PPC64_ELF_ABI_V1, it's 112, for ABI_V2, it's 48. So the nip will read a wrong value from stack when ABI_V2 enabled. To determine if ABI_V2 enabled is tricky. This patch do it by check the following: In arch/powerpc/include/asm/ppc_asm.h: #ifdef CONFIG_PPC64_ELF_ABI_V2 #define STK_GOT 24 #else #define STK_GOT 40 In arch/powerpc/kernel/tm.S: _GLOBAL(tm_reclaim) mfcr r5 mflr r0 stw r5, 8(r1) std r0, 16(r1) std r2, STK_GOT(r1) ... So a disassemble on tm_reclaim, and extract the STK_GOT value from std instruction is used as the approach. After the patch: crash> bt 1 PID: 1 TASK: c000000003714b80 CPU: 2 COMMAND: "systemd" #0 [c0000000037737d0] __schedule at c00000000112e4ec #1 [c0000000037738b0] schedule at c00000000112ea80 ... Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; --- This patch is the follow-up of gdb stack unwinding support v7 discussion[1], where a "gdb bt" fail is observed. After applying the patch, the "gdb bt" can also work normal for gdb stack unwinding support v7. [1]: https://www.mail-archive.com/devel@lists.crash-utility.osci.io/msg01120.html --- defs.h | 1 + ppc64.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 57 insertions(+), 3 deletions(-) diff --git a/defs.h b/defs.h index 2231cb6..d5cb8cc 100644 --- a/defs.h +++ b/defs.h @@ -4643,6 +4643,7 @@ struct efi_memory_desc_t { #define MSR_PR_LG 14 /* Problem State / Privilege Level */ /* Used to find the user or kernel-mode frame*/ +#define STACK_SWITCH_FRAME_REGS 48 #define STACK_FRAME_OVERHEAD 112 #define EXCP_FRAME_MARKER 0x7265677368657265 diff --git a/ppc64.c b/ppc64.c index e8930a1..5e2595e 100644 --- a/ppc64.c +++ b/ppc64.c @@ -2813,6 +2813,51 @@ ppc64_get_sp(ulong task) return sp; } +static bool +is_ppc64_elf_abi_v2(void) +{ + char buf1[BUFSIZE]; + char *pos1, *pos2; + int errflag = 0; + ulong stk_got = 0; + static bool ret = false; + static bool checked = false; + + if (checked == true || !symbol_exists("tm_reclaim")) + return ret; + + sprintf(buf1, "x/16i tm_reclaim"); + open_tmpfile(); + if (!gdb_pass_through(buf1, pc->tmpfile, GNU_RETURN_ON_ERROR)) + goto out; + checked = true; + rewind(pc->tmpfile); + while (fgets(buf1, BUFSIZE, pc->tmpfile)) { + // "std r2, STK_GOT(r1)" is expected + if (strstr(buf1, "std") && + strstr(buf1, "(r1)") && + (pos1 = strstr(buf1, "r2,"))) { + pos1 += strlen("r2,"); + for (pos2 = pos1; *pos2 != '\0' && *pos2 != '('; pos2++); + *pos2 = '\0'; + stk_got = stol(pos1, RETURN_ON_ERROR|QUIET, &errflag); + break; + } + } + + if (!errflag) { + switch (stk_got) { + case 24: + ret = true; + case 40: + goto out; + } + } + error(WARNING, "Unstable elf_abi v1/v2 detection.\n"); +out: + close_tmpfile(); + return ret; +} /* * get the SP and PC values for idle tasks. @@ -2834,9 +2879,17 @@ get_ppc64_frame(struct bt_info *bt, ulong *getpc, ulong *getsp) sp = ppc64_get_sp(task); if (!INSTACK(sp, bt)) goto out; - readmem(sp+STACK_FRAME_OVERHEAD, KVADDR, &regs, - sizeof(struct ppc64_pt_regs), - "PPC64 pt_regs", FAULT_ON_ERROR); + + if (THIS_KERNEL_VERSION >= LINUX(6,2,0) && is_ppc64_elf_abi_v2()) { + readmem(sp+STACK_SWITCH_FRAME_REGS, KVADDR, &regs, + sizeof(struct ppc64_pt_regs), + "PPC64 pt_regs", FAULT_ON_ERROR); + } else { + readmem(sp+STACK_FRAME_OVERHEAD, KVADDR, &regs, + sizeof(struct ppc64_pt_regs), + "PPC64 pt_regs", FAULT_ON_ERROR); + } + ip = regs.nip; closest = closest_symbol(ip); if (STREQ(closest, ".__switch_to") || STREQ(closest, "__switch_to")) { -- 2.40.1