Re: [Crash-utility] [PATCH 11/16] MIPS64: Fixes for the gathering of the active task registers for the 'bt' command

dumpfiles: (1) If ELF notes are not available, read them from the kernel's crash_notes.

(2) If an online CPUs did not save its ELF notes, then adjust the mapping of each ELF note to its CPU accordingly. E.g. With this patch: crash> bt PID: 4768 TASK: 9800000243bcf200 CPU: 3 COMMAND: "bash" #0 [980000024291f930] __crash_kexec at ffffffff802fff84 #1 [980000024291faa0] panic at ffffffff80248cac #2 [980000024291fb40] die at ffffffff8021b338 #3 [980000024291fb70] do_page_fault at ffffffff802315e0 #4 [980000024291fbd0] tlb_do_page_fault_1 at ffffffff80239388 #5 [980000024291fd00] sysrq_handle_crash at ffffffff8085d308 #6 [980000024291fd10] __handle_sysrq at ffffffff8085d9e0 #7 [980000024291fd60] write_sysrq_trigger at ffffffff8085e020 #8 [980000024291fd80] proc_reg_write at ffffffff804762f0 #9 [980000024291fda0] __vfs_write at ffffffff803f3138 Signed-off-by: Huacai Chen <chenhuacai(a)loongson.cn&gt; Signed-off-by: Youling Tang <tangyouling(a)loongson.cn&gt; --- mips64.c | 203 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 202 insertions(+), 1 deletion(-) diff --git a/mips64.c b/mips64.c index 57a7f41..d949af4 100644 --- a/mips64.c +++ b/mips64.c @@ -42,7 +42,9 @@ static void mips64_get_stack_frame(struct bt_info *bt, ulong *pcp, ulong *spp); static int mips64_get_dumpfile_stack_frame(struct bt_info *bt, ulong *nip, ulong *ksp); static int mips64_get_frame(struct bt_info *bt, ulong *pcp, ulong *spp); - +static int mips64_init_active_task_regs(void); +static int mips64_get_crash_notes(void); +static int mips64_get_elf_notes(void); /* * 3 Levels paging PAGE_SIZE=16KB @@ -806,6 +808,192 @@ mips64_get_frame(struct bt_info *bt, ulong *pcp, ulong *spp) return TRUE; } +static int +mips64_init_active_task_regs(void) +{ + int retval; + + retval = mips64_get_crash_notes(); + if (retval == TRUE) + return retval; + + return mips64_get_elf_notes(); +} + +/* + * Retrieve task registers for the time of the crash. + */ +static int +mips64_get_crash_notes(void) +{ + struct machine_specific *ms = machdep->machspec; + ulong crash_notes; + Elf64_Nhdr *note; + ulong offset; + char *buf, *p; + ulong *notes_ptrs; + ulong i; + + /* + * crash_notes contains per cpu memory for storing cpu states + * in case of system crash. + */ + if (!symbol_exists("crash_notes")) + return FALSE; + + crash_notes = symbol_value("crash_notes"); + + notes_ptrs = (ulong *)GETBUF(kt->cpus*sizeof(notes_ptrs[0])); + + /* + * Read crash_notes for the first CPU. crash_notes are in standard ELF + * note format. + */ + if (!readmem(crash_notes, KVADDR, &notes_ptrs[kt->cpus-1], + sizeof(notes_ptrs[kt->cpus-1]), "crash_notes", + RETURN_ON_ERROR)) { + error(WARNING, "cannot read crash_notes\n"); + FREEBUF(notes_ptrs); + return FALSE; + } + + if (symbol_exists("__per_cpu_offset")) { + + /* + * Add __per_cpu_offset for each cpu to form the pointer to the notes + */ + for (i = 0; i < kt->cpus; i++) + notes_ptrs[i] = notes_ptrs[kt->cpus-1] + kt->__per_cpu_offset[i]; + } + + buf = GETBUF(SIZE(note_buf)); + + if (!(panic_task_regs = calloc((size_t)kt->cpus, sizeof(*panic_task_regs)))) + error(FATAL, "cannot calloc panic_task_regs space\n"); + + for (i = 0; i < kt->cpus; i++) { + + if (!readmem(notes_ptrs[i], KVADDR, buf, SIZE(note_buf), "note_buf_t", + RETURN_ON_ERROR)) { + error(WARNING, + "cannot find NT_PRSTATUS note for cpu: %d\n", i); + goto fail; + } + + /* + * Do some sanity checks for this note before reading registers from it. + */ + note = (Elf64_Nhdr *)buf; + p = buf + sizeof(Elf64_Nhdr); + + /* + * dumpfiles created with qemu won't have crash_notes, but there will + * be elf notes; dumpfiles created by kdump do not create notes for + * offline cpus. + */ + if (note->n_namesz == 0 && (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE())) { + if (DISKDUMP_DUMPFILE()) + note = diskdump_get_prstatus_percpu(i); + else if (KDUMP_DUMPFILE()) + note = netdump_get_prstatus_percpu(i); + if (note) { + /* + * SIZE(note_buf) accounts for a "final note", which is a + * trailing empty elf note header. + */ + long notesz = SIZE(note_buf) - sizeof(Elf64_Nhdr); + + if (sizeof(Elf64_Nhdr) + roundup(note->n_namesz, 4) + + note->n_descsz == notesz) + BCOPY((char *)note, buf, notesz); + } else { + error(WARNING, + "cannot find NT_PRSTATUS note for cpu: %d\n", i); + continue; + } + } + + /* + * Check the sanity of NT_PRSTATUS note only for each online cpu. + */ + if (note->n_type != NT_PRSTATUS) { + error(WARNING, "invalid NT_PRSTATUS note (n_type != NT_PRSTATUS)\n"); + goto fail; + } + if (!STRNEQ(p, "CORE")) { + error(WARNING, "invalid NT_PRSTATUS note (name != \"CORE\"\n"); + goto fail; + } + + /* + * Find correct location of note data. This contains elf_prstatus + * structure which has registers etc. for the crashed task. + */ + offset = sizeof(Elf64_Nhdr); + offset = roundup(offset + note->n_namesz, 4); + p = buf + offset; /* start of elf_prstatus */ + + BCOPY(p + OFFSET(elf_prstatus_pr_reg), &panic_task_regs[i], + sizeof(panic_task_regs[i])); + } + + /* + * And finally we have the registers for the crashed task. This is + * used later on when dumping backtrace. + */ + ms->crash_task_regs = panic_task_regs; + + FREEBUF(buf); + FREEBUF(notes_ptrs); + return TRUE; + +fail: + FREEBUF(buf); + FREEBUF(notes_ptrs); + free(panic_task_regs); + return FALSE; +} + +static int +mips64_get_elf_notes(void) +{ + struct machine_specific *ms = machdep->machspec; + int i; + + if (!DISKDUMP_DUMPFILE() && !KDUMP_DUMPFILE()) + return FALSE; + + panic_task_regs = calloc(kt->cpus, sizeof(*panic_task_regs)); + if (!panic_task_regs) + error(FATAL, "cannot calloc panic_task_regs space\n"); + + for (i = 0; i < kt->cpus; i++) { + Elf64_Nhdr *note = NULL; + size_t len; + + if (DISKDUMP_DUMPFILE()) + note = diskdump_get_prstatus_percpu(i); + else if (KDUMP_DUMPFILE()) + note = netdump_get_prstatus_percpu(i); + + if (!note) { + error(WARNING, + "cannot find NT_PRSTATUS note for cpu: %d\n", i); + continue; + } + + len = sizeof(Elf64_Nhdr); + len = roundup(len + note->n_namesz, 4); + + BCOPY((char *)note + len + OFFSET(elf_prstatus_pr_reg), + &panic_task_regs[i], sizeof(panic_task_regs[i])); + } + + ms->crash_task_regs = panic_task_regs; + + return TRUE; +} + /* * Accept or reject a symbol from the kernel namelist. */ @@ -959,9 +1147,22 @@ mips64_init(int when) mips64_stackframe_init(); if (!machdep->hz) machdep->hz = 250; + MEMBER_OFFSET_INIT(elf_prstatus_pr_reg, "elf_prstatus", + "pr_reg"); + STRUCT_SIZE_INIT(note_buf, "note_buf_t"); break; case POST_VM: + /* + * crash_notes contains machine specific information about the + * crash. In particular, it contains CPU registers at the time + * of the crash. We need this information to extract correct + * backtraces from the panic task. + */ + if (!ACTIVE() && !mips64_init_active_task_regs()) + error(WARNING, + "cannot retrieve registers for active task%s\n\n", + kt->cpus > 1 ? "s" : ""); break; } } -- 2.1.0