Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces
From: Petr Mladek <pmladek@suse.com>
Date: 2021-03-30 10:30:04
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lkml
On Tue 2021-03-23 19:04:35, Stephen Boyd wrote:
Let's make kernel stacktraces easier to identify by including the build ID[1] of a module if the stacktrace is printing a symbol from a module. Example: WARNING: CPU: 3 PID: 3373 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm] Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE hci_uart <modules trimmed> CPU: 3 PID: 3373 Comm: bash Not tainted 5.11 #12 a8c0d47f7051f3e6670ceaea724af66a39c6cec8
I tested it with "echo l >/proc/sysrq-trigger" and I got the following output: [ 71.905593] CPU: 0 PID: 1762 Comm: bash Kdump: loaded Not tainted 5.12.0-rc5-default+ #167 00000080ffffffff0000000000000000 00000000 It does not looks like an unique build-id. Any idea what was going wrong?
quoted hunk ↗ jump to hunk
--- a/include/linux/kallsyms.h +++ b/include/linux/kallsyms.h@@ -91,6 +93,7 @@ const char *kallsyms_lookup(unsigned long addr, /* Look up a kernel symbol and return it in a text buffer. */ extern int sprint_symbol(char *buffer, unsigned long address); +extern int sprint_symbol_stacktrace(char *buffer, unsigned long address); extern int sprint_symbol_no_offset(char *buffer, unsigned long address); extern int sprint_backtrace(char *buffer, unsigned long address);
Could we use a more clear name? It is hard to guess what is the difference between sprint_*_stacktrace() and sprint_backtrace(). What about sprint_symbol_build_id() ?
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diff --git a/kernel/module.c b/kernel/module.c index 30479355ab85..9e9cb502fb33 100644 --- a/kernel/module.c +++ b/kernel/module.c@@ -2770,6 +2771,20 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) } mod->core_kallsyms.num_symtab = ndst; } + +static void init_build_id(struct module *mod, const struct load_info *info) +{ + const Elf_Shdr *sechdr; + unsigned int i; + + for (i = 0; i < info->hdr->e_shnum; i++) { + sechdr = &info->sechdrs[i]; + if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE && + !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id, + sechdr->sh_size)) + break; + }
Just to be sure. Is this really reliable way how to find the build ID, please?
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+} #else static inline void layout_symtab(struct module *mod, struct load_info *info) {@@ -2778,6 +2793,10 @@ static inline void layout_symtab(struct module *mod, struct load_info *info) static void add_kallsyms(struct module *mod, const struct load_info *info) { }
Best Regards, Petr