The %pS printk format (among some others) is used to print kernel
addresses symbolically. When the kernel prints an address inside of a
module, the kernel prints the addresses' symbol name along with the
module's name that contains the address. Let's make kernel stacktraces
easier to identify on KALLSYMS builds by including the build ID of a
module when we print the address.
This is especially helpful for crash debugging with pstore or crashdump
kernels. If we have the build ID for the module in the stacktrace we can
request the debug symbols for the module from a remote debuginfod server
or parse stacktraces at a later time with decode_stacktrace.sh by
downloading the correct symbols based on the build ID. This cuts down on
the amount of time and effort needed to find the correct kernel modules
for a stacktrace by encoding that information into it.
An alternative to changing the printk format would be to update the
"Modules linked in:" line to include the build ID of each module linked
in. This can become quite long when many modules are loaded (i.e. on a
distro) so I've opted for the printk format instead. Similarly,
collecting each module build ID in a stacktrace and then printing it
after the trace would require some architecture level surgery to the
dump stack code and also provide the ID "too late" for code that is
parsing each line of the stacktrace.
Example:
WARNING: CPU: 4 PID: 3255 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm] (ed5019fdf5e53be37cb1ba7899292d7e143b259e)
Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE
CPU: 4 PID: 3255 Comm: bash Not tainted 5.11 #3 aa23f7a1231c229de205662d5a9e0d4c580f19a1
Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--)
pc : lkdtm_WARNING+0x28/0x30 [lkdtm] (ed5019fdf5e53be37cb1ba7899292d7e143b259e)
lr : lkdtm_do_action+0x24/0x40 [lkdtm] (ed5019fdf5e53be37cb1ba7899292d7e143b259e)
sp : ffffffc0134fbca0
x29: ffffffc0134fbca0 x28: ffffff92d53ba240
x27: 0000000000000000 x26: 0000000000000000
x25: 0000000000000000 x24: ffffffe3622352c0
x23: 0000000000000020 x22: ffffffe362233366
x21: ffffffe3622352e0 x20: ffffffc0134fbde0
x19: 0000000000000008 x18: 0000000000000000
x17: ffffff929b6536fc x16: 0000000000000000
x15: 0000000000000000 x14: 0000000000000012
x13: ffffffe380ed892c x12: ffffffe381d05068
x11: 0000000000000000 x10: 0000000000000000
x9 : 0000000000000001 x8 : ffffffe362237000
x7 : aaaaaaaaaaaaaaaa x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000001
x3 : 0000000000000008 x2 : ffffff93fef25a70
x1 : ffffff93fef15788 x0 : ffffffe3622352e0
Call trace:
lkdtm_WARNING+0x28/0x30 [lkdtm] (ed5019fdf5e53be37cb1ba7899292d7e143b259e)
direct_entry+0x16c/0x1b4 [lkdtm] (ed5019fdf5e53be37cb1ba7899292d7e143b259e)
full_proxy_write+0x74/0xa4
vfs_write+0xec/0x2e8
ksys_write+0x84/0xf0
__arm64_sys_write+0x24/0x30
el0_svc_common+0xf4/0x1c0
do_el0_svc_compat+0x28/0x3c
el0_svc_compat+0x10/0x1c
el0_sync_compat_handler+0xa8/0xcc
el0_sync_compat+0x178/0x180
---[ end trace 3d95032303e59e68 ]---
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Evan Green <evgreen@xxxxxxxxxxxx>
Cc: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: <linux-doc@xxxxxxxxxxxxxxx>
Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
---
Yet another alternative is to add a printk format like %pSB for
backtrace prints. This would require a handful of architecture updates
and I'm not sure it's worth the effort for that.
Documentation/core-api/printk-formats.rst | 6 +++
include/linux/kallsyms.h | 6 ++-
include/linux/module.h | 2 +-
kernel/kallsyms.c | 45 +++++++++++++++--------
kernel/module.c | 4 +-
5 files changed, 44 insertions(+), 19 deletions(-)
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 160e710d992f..7f05962f7f68 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -114,6 +114,12 @@ used when printing stack backtraces. The specifier takes into
consideration the effect of compiler optimisations which may occur
when tail-calls are used and marked with the noreturn GCC attribute.
+If the pointer is within a module, the module name and build ID is printed after
+the symbol name.
+
+::
+ %pS versatile_init+0x0/0x110 [module_name] (ed5019fdf5e53be37cb1ba7899292d7e143b259e)
+
Probed Pointers from BPF / tracing
----------------------------------
diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 465060acc981..c2f1660823cb 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -7,6 +7,7 @@
#define _LINUX_KALLSYMS_H
#include <linux/errno.h>
+#include <linux/buildid.h>
#include <linux/kernel.h>
#include <linux/stddef.h>
#include <linux/mm.h>
@@ -15,8 +16,9 @@
#include <asm/sections.h>
#define KSYM_NAME_LEN 128
-#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + (KSYM_NAME_LEN - 1) + \
- 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + 1)
+#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s] (%s)") + (KSYM_NAME_LEN - 1) + \
+ 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + \
+ (BUILD_ID_STR_SIZE_MAX - 1) + 1)
struct cred;
struct module;
diff --git a/include/linux/module.h b/include/linux/module.h
index 9d1f6a5240c1..c12f9215f63e 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -634,7 +634,7 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr);
const char *module_address_lookup(unsigned long addr,
unsigned long *symbolsize,
unsigned long *offset,
- char **modname,
+ char **modname, char **modbuildid,
char *namebuf);
int lookup_module_symbol_name(unsigned long addr, char *symname);
int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 8043a90aa50e..a70c53764b8a 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -273,21 +273,13 @@ int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
get_symbol_pos(addr, symbolsize, offset);
return 1;
}
- return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
+ return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
!!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
}
-/*
- * Lookup an address
- * - modname is set to NULL if it's in the kernel.
- * - We guarantee that the returned name is valid until we reschedule even if.
- * It resides in a module.
- * - We also guarantee that modname will be valid until rescheduled.
- */
-const char *kallsyms_lookup(unsigned long addr,
- unsigned long *symbolsize,
- unsigned long *offset,
- char **modname, char *namebuf)
+const char *kallsyms_lookup_buildid(unsigned long addr, unsigned long *symbolsize,
+ unsigned long *offset, char **modname,
+ char **modbuildid, char *namebuf)
{
const char *ret;
@@ -303,12 +295,14 @@ const char *kallsyms_lookup(unsigned long addr,
namebuf, KSYM_NAME_LEN);
if (modname)
*modname = NULL;
+ if (modbuildid)
+ *modbuildid = NULL;
return namebuf;
}
/* See if it's in a module or a BPF JITed image. */
ret = module_address_lookup(addr, symbolsize, offset,
- modname, namebuf);
+ modname, modbuildid, namebuf);
if (!ret)
ret = bpf_address_lookup(addr, symbolsize,
offset, modname, namebuf);
@@ -319,6 +313,22 @@ const char *kallsyms_lookup(unsigned long addr,
return ret;
}
+/*
+ * Lookup an address
+ * - modname is set to NULL if it's in the kernel.
+ * - We guarantee that the returned name is valid until we reschedule even if.
+ * It resides in a module.
+ * - We also guarantee that modname will be valid until rescheduled.
+ */
+const char *kallsyms_lookup(unsigned long addr,
+ unsigned long *symbolsize,
+ unsigned long *offset,
+ char **modname, char *namebuf)
+{
+ return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
+ NULL, namebuf);
+}
+
int lookup_symbol_name(unsigned long addr, char *symname)
{
symname[0] = '\0';
@@ -362,12 +372,14 @@ static int __sprint_symbol(char *buffer, unsigned long address,
int symbol_offset, int add_offset)
{
char *modname;
+ char *modbuildid;
const char *name;
unsigned long offset, size;
int len;
address += symbol_offset;
- name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
+ name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &modbuildid,
+ buffer);
if (!name)
return sprintf(buffer, "0x%lx", address - symbol_offset);
@@ -379,8 +391,11 @@ static int __sprint_symbol(char *buffer, unsigned long address,
if (add_offset)
len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
- if (modname)
+ if (modname) {
len += sprintf(buffer + len, " [%s]", modname);
+ if (modbuildid)
+ len += sprintf(buffer + len, " (%s)", modbuildid);
+ }
return len;
}
diff --git a/kernel/module.c b/kernel/module.c
index a7559a0de9d8..2909e62f147b 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4255,7 +4255,7 @@ void * __weak dereference_module_function_descriptor(struct module *mod,
const char *module_address_lookup(unsigned long addr,
unsigned long *size,
unsigned long *offset,
- char **modname,
+ char **modname, char **modbuildid,
char *namebuf)
{
const char *ret = NULL;
@@ -4266,6 +4266,8 @@ const char *module_address_lookup(unsigned long addr,
if (mod) {
if (modname)
*modname = mod->name;
+ if (modbuildid)
+ *modbuildid = mod->build_id;
ret = find_kallsyms_symbol(mod, addr, size, offset);
}
--
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