[Crash-utility] Re: [PATCH] arm64: determine the crash note size when note_buf_t is absent

From: Pu Hu <hupu(a)transsion.com&gt; note_buf_t is a typedef of a u32 array. Clang often omits it from vmlinux DWARF even when the crash_notes symbol is present. SIZE(note_buf) then aborts session startup: crash: invalid structure size: note_buf FILE: arm64.c FUNCTION: arm64_get_crash_notes() Look up note_buf_t first and note_buf second. When neither type is available, measure one NT_PRSTATUS note from the per-cpu crash note in memory and include the terminating empty Elf note header. The length stays local to arm64_get_crash_notes() and is not written into size_table. If it still cannot be determined, warn and continue so a raw RAM dump can be opened. A vmlinux that already contains note_buf_t keeps the previous size. No constant note length is introduced.

Signed-off-by: Pu Hu <hupu(a)transsion.com&gt; --- arm64.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 86 insertions(+), 4 deletions(-) diff --git a/arm64.c b/arm64.c index 39f745b..4f0b621 --- a/arm64.c +++ b/arm64.c @@ -2788,6 +2788,8 @@ arm64_stackframe_init(void) struct syment *sp1, *sp1n, *sp2, *sp2n, *sp3, *sp3n; STRUCT_SIZE_INIT(note_buf, "note_buf_t"); + if (INVALID_SIZE(note_buf)) + STRUCT_SIZE_INIT(note_buf, "note_buf"); STRUCT_SIZE_INIT(elf_prstatus, "elf_prstatus"); MEMBER_OFFSET_INIT(elf_prstatus_pr_pid, "elf_prstatus", "pr_pid"); MEMBER_OFFSET_INIT(elf_prstatus_pr_reg, "elf_prstatus", "pr_reg"); @@ -5053,6 +5055,78 @@ arm64_get_smp_cpus(void) } +/* + * Bytes described by one Elf note header: header + aligned name + descriptor. + * Returns 0 when the header cannot be a crash NT_PRSTATUS note. + */ +static long +arm64_note_size_from_mem(ulong addr) +{ + Elf64_Nhdr hdr; + long size, limit; + + if (!addr) + return 0; + + if (!readmem(addr, KVADDR, &hdr, sizeof(hdr), + "Elf64_Nhdr", RETURN_ON_ERROR|QUIET)) + return 0; + + /* + * A corrupt header must not become an allocation size. + * NT_PRSTATUS names are short; one elf_prstatus fits in a page. + */ + limit = PAGESIZE() ? PAGESIZE() : 4096; + if (hdr.n_type != NT_PRSTATUS) + return 0; + if (!hdr.n_namesz || hdr.n_namesz > 256) + return 0; + if (!hdr.n_descsz || hdr.n_descsz > limit) + return 0; + + size = sizeof(hdr); + size = roundup(size + hdr.n_namesz, 4); + size += hdr.n_descsz; + size = roundup(size, 4); + /* note_buf_t also contains the terminating empty note */ + size += sizeof(hdr); + return size; +} + +/* + * Bytes to read from one per-cpu crash note. + * + * Use the vmlinux type when it exists. note_buf_t is a typedef of a u32 + * array and Clang often omits it from DWARF, so SIZE(note_buf) would + * abort startup. In that case measure the NT_PRSTATUS note that is + * actually stored. The result is local to arm64_get_crash_notes() and + * is not written back to size_table. + * + * Returns a positive size, or 0 if it cannot be determined. + */ +static long +arm64_crash_note_size(ulong *notes_ptrs) +{ + long sz; + ulong i; + + if (VALID_SIZE(note_buf) && size_table.note_buf > 0) + return size_table.note_buf; + + if (!notes_ptrs) + return 0; + + for (i = 0; i < kt->cpus; i++) { + sz = arm64_note_size_from_mem(notes_ptrs[i]); + if (sz > 0) { + if (CRASHDEBUG(1)) + fprintf(fp, "arm64_crash_note_size: %ld\n", sz); + return sz; + } + } + return 0; +} + /* * Retrieve task registers for the time of the crash. */ @@ -5066,6 +5140,7 @@ arm64_get_crash_notes(void) char *buf, *p; ulong *notes_ptrs; ulong i, found; + long note_sz; if (!symbol_exists("crash_notes")) { if (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE()) { @@ -5127,13 +5202,20 @@ arm64_get_crash_notes(void) notes_ptrs[i] = notes_ptrs[kt->cpus-1] + kt->__per_cpu_offset[i]; } - buf = GETBUF(SIZE(note_buf)); + note_sz = arm64_crash_note_size(notes_ptrs); + if (note_sz <= 0) { + error(WARNING, "cannot determine size of note_buf_t\n"); + FREEBUF(notes_ptrs); + return; + } + + buf = GETBUF(note_sz); if (!(ms->panic_task_regs = calloc((size_t)kt->cpus, sizeof(struct arm64_pt_regs)))) error(FATAL, "cannot calloc panic_task_regs space\n"); for (i = found = 0; i < kt->cpus; i++) { - if (!readmem(notes_ptrs[i], KVADDR, buf, SIZE(note_buf), + if (!readmem(notes_ptrs[i], KVADDR, buf, note_sz, "note_buf_t", RETURN_ON_ERROR)) { error(WARNING, "cpu %d: cannot read NT_PRSTATUS note\n", i); continue; @@ -5157,10 +5239,10 @@ arm64_get_crash_notes(void) note = netdump_get_prstatus_percpu(i); if (note) { /* - * SIZE(note_buf) accounts for a "final note", which is a + * note_sz accounts for a "final note", which is a * trailing empty elf note header. */ - long notesz = SIZE(note_buf) - sizeof(Elf64_Nhdr); + long notesz = note_sz - sizeof(Elf64_Nhdr); if (sizeof(Elf64_Nhdr) + roundup(note->n_namesz, 4) + note->n_descsz == notesz)