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Message-ID: <161835466995.3764895.13268854960596303989@swboyd.mtv.corp.google.com>
Date: Tue, 13 Apr 2021 15:57:49 -0700
From: Stephen Boyd <swboyd@...omium.org>
To: Petr Mladek <pmladek@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Jessica Yu <jeyu@...nel.org>,
Evan Green <evgreen@...omium.org>,
Hsin-Yi Wang <hsinyi@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-doc@...r.kernel.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces
Quoting Petr Mladek (2021-04-13 08:01:14)
> On Fri 2021-04-09 18:52:52, 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.
> > This makes it simpler for developers to locate a kernel module's full
> > debuginfo for a particular stacktrace. Combined with
> > scripts/decode_stracktrace.sh, a developer can download the matching
> > debuginfo from a debuginfod[2] server and find the exact file and line
> > number for the functions plus offsets in a stacktrace that match the
> > module. This is especially useful for pstore crash debugging where the
> > kernel crashes are recorded in something like console-ramoops and the
> > recovery kernel/modules are different or the debuginfo doesn't exist on
> > the device due to space concerns (the debuginfo can be too large for
> > space limited devices).
> >
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index 59f094fa6f74..4bf869f6c944 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -11,6 +11,7 @@
> >
> > #include <linux/list.h>
> > #include <linux/stat.h>
> > +#include <linux/buildid.h>
> > #include <linux/compiler.h>
> > #include <linux/cache.h>
> > #include <linux/kmod.h>
> > @@ -367,6 +368,9 @@ struct module {
> > /* Unique handle for this module */
> > char name[MODULE_NAME_LEN];
> >
> > + /* Module build ID */
> > + unsigned char build_id[BUILD_ID_SIZE_MAX];
>
> Do we want to initialize/store the ID even when
> CONFIG_STACKTRACE_BUILD_ID is disabled and nobody would
> use it?
>
> Most struct module members are added only when the related feature
> is enabled.
>
> I am not sure how it would complicate the code. It is possible
> that it is not worth it. Well, I could imagine that the API
> will always pass the buildid parameter and
> module_address_lookup() might do something like
>
> #ifndef CONFIG_STACKTRACE_BUILD_ID
> static char empty_build_id[BUILD_ID_SIZE_MAX];
> #endif
>
> if (modbuildid) {
> if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID))
> *modbuildid = mod->build_id;
> else
> *modbuildid = empty_build_id;
>
> IMHO, this is primary a call for Jessica as the module code maintainer.
>
> Otherwise, I am fine with this patch. And it works as expected.
>
Does declaring mod->build_id as zero length work well enough?
----8<----
diff --git a/include/linux/module.h b/include/linux/module.h
index 4bf869f6c944..03b2f6af093a 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -359,6 +359,12 @@ struct klp_modinfo {
};
#endif
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+#define MODULE_BUILD_ID_LEN BUILD_ID_SIZE_MAX
+#else
+#define MODULE_BUILD_ID_LEN 0
+#endif
+
struct module {
enum module_state state;
@@ -369,7 +375,7 @@ struct module {
char name[MODULE_NAME_LEN];
/* Module build ID */
- unsigned char build_id[BUILD_ID_SIZE_MAX];
+ unsigned char build_id[MODULE_BUILD_ID_LEN];
/* Sysfs stuff. */
struct module_kobject mkobj;
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index b835992e76c2..ebd5b30c3039 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -25,7 +25,10 @@
#include <linux/filter.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
+#include <linux/build_bug.h>
#include <linux/compiler.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
/*
* These will be re-linked against their real values
@@ -393,10 +396,13 @@ static int __sprint_symbol(char *buffer, unsigned long address,
if (modname) {
len += sprintf(buffer + len, " [%s", modname);
- /* build ID should match length of sprintf below */
- BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
- if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+ if (add_buildid && buildid) {
+ /* build ID should match length of sprintf */
+ static_assert(MODULE_BUILD_ID_LEN == 20);
len += sprintf(buffer + len, " %20phN", buildid);
+ }
+#endif
len += sprintf(buffer + len, "]");
}
diff --git a/kernel/module.c b/kernel/module.c
index 6f5bc1b046a5..a0d222fbd281 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2771,7 +2771,17 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
}
mod->core_kallsyms.num_symtab = ndst;
}
+#else
+static inline void layout_symtab(struct module *mod, struct load_info *info)
+{
+}
+
+static void add_kallsyms(struct module *mod, const struct load_info *info)
+{
+}
+#endif /* CONFIG_KALLSYMS */
+#if IS_ENABLED(CONFIG_KALLSYMS) && IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
static void init_build_id(struct module *mod, const struct load_info *info)
{
const Elf_Shdr *sechdr;
@@ -2786,18 +2796,10 @@ static void init_build_id(struct module *mod, const struct load_info *info)
}
}
#else
-static inline void layout_symtab(struct module *mod, struct load_info *info)
-{
-}
-
-static void add_kallsyms(struct module *mod, const struct load_info *info)
-{
-}
-
static void init_build_id(struct module *mod, const struct load_info *info)
{
}
-#endif /* CONFIG_KALLSYMS */
+#endif
static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
{
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