linux/Documentation/core-api
Stephen Boyd 9294523e37 module: add printk formats to add module build ID to stacktraces
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).

Originally, I put this on the %pS format, but that was quickly rejected
given that %pS is used in other places such as ftrace where build IDs
aren't meaningful.  There was some discussions on the list to put every
module build ID into the "Modules linked in:" section of the stacktrace
message but that quickly becomes very hard to read once you have more than
three or four modules linked in.  It also provides too much information
when we don't expect each module to be traversed in a stacktrace.  Having
the build ID for modules that aren't important just makes things messy.
Splitting it to multiple lines for each module quickly explodes the number
of lines printed in an oops too, possibly wrapping the warning off the
console.  And finally, trying to stash away each module used in a
callstack to provide the ID of each symbol printed is cumbersome and would
require changes to each architecture to stash away modules and return
their build IDs once unwinding has completed.

Instead, we opt for the simpler approach of introducing new printk formats
'%pS[R]b' for "pointer symbolic backtrace with module build ID" and '%pBb'
for "pointer backtrace with module build ID" and then updating the few
places in the architecture layer where the stacktrace is printed to use
this new format.

Before:

 Call trace:
  lkdtm_WARNING+0x28/0x30 [lkdtm]
  direct_entry+0x16c/0x1b4 [lkdtm]
  full_proxy_write+0x74/0xa4
  vfs_write+0xec/0x2e8

After:

 Call trace:
  lkdtm_WARNING+0x28/0x30 [lkdtm 6c2215028606bda50de823490723dc4bc5bf46f9]
  direct_entry+0x16c/0x1b4 [lkdtm 6c2215028606bda50de823490723dc4bc5bf46f9]
  full_proxy_write+0x74/0xa4
  vfs_write+0xec/0x2e8

[akpm@linux-foundation.org: fix build with CONFIG_MODULES=n, tweak code layout]
[rdunlap@infradead.org: fix build when CONFIG_MODULES is not set]
  Link: https://lkml.kernel.org/r/20210513171510.20328-1-rdunlap@infradead.org
[akpm@linux-foundation.org: make kallsyms_lookup_buildid() static]
[cuibixuan@huawei.com: fix build error when CONFIG_SYSFS is disabled]
  Link: https://lkml.kernel.org/r/20210525105049.34804-1-cuibixuan@huawei.com

Link: https://lkml.kernel.org/r/20210511003845.2429846-6-swboyd@chromium.org
Link: https://fedoraproject.org/wiki/Releases/FeatureBuildId [1]
Link: https://sourceware.org/elfutils/Debuginfod.html [2]
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Bixuan Cui <cuibixuan@huawei.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Evan Green <evgreen@chromium.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-08 11:48:22 -07:00
..
irq irqdomain: Kill irq_domain_add_legacy_isa 2021-06-10 13:09:17 +01:00
assoc_array.rst Documentation: Use "while" instead of "whilst" 2018-11-20 09:30:43 -07:00
boot-time-mm.rst docs/boot-time-mm: remove bootmem documentation 2018-10-31 08:54:16 -07:00
bus-virt-phys-mapping.rst docs: core-api: avoid using ReST :doc:foo markup 2021-06-17 13:24:37 -06:00
cachetlb.rst mm/vmalloc: remove unmap_kernel_range 2021-04-30 11:20:40 -07:00
circular-buffers.rst doc: Remove ".vnet" from paulmck email addresses 2019-05-28 09:02:57 -07:00
cpu_hotplug.rst Documentation: core-api/cpu_hotplug: fix a typo 2020-09-09 11:42:09 -06:00
debug-objects.rst doc: debugobjects: actually pull in the kerneldoc comments 2016-11-29 14:44:14 -07:00
debugging-via-ohci1394.rst docs: debugging-via-ohci1394.txt: add it to the core-api book 2020-05-15 11:59:17 -06:00
dma-api-howto.rst docs: move DMA kAPI to Documentation/core-api 2020-05-15 11:51:54 -06:00
dma-api.rst docs: core-api: avoid using ReST :doc:foo markup 2021-06-17 13:24:37 -06:00
dma-attributes.rst dma-mapping: add a new dma_alloc_pages API 2020-09-25 06:20:47 +02:00
dma-isa-lpc.rst docs: core-api: avoid using ReST :doc:foo markup 2021-06-17 13:24:37 -06:00
errseq.rst errseq: Add to documentation tree 2018-01-01 12:40:27 -07:00
genalloc.rst lib/genalloc.c: rename addr_in_gen_pool to gen_pool_has_addr 2019-12-04 19:44:13 -08:00
generic-radix-tree.rst generic radix trees 2019-03-12 10:04:02 -07:00
genericirq.rst docs: genericirq.rst: don't document chip.c functions twice 2020-10-15 07:49:41 +02:00
gfp_mask-from-fs-io.rst docs: core-api/gfp_mask-from-fs-io: add a label for cross-referencing 2018-09-20 11:02:32 -06:00
idr.rst Core-api: Documentation: Replace deprecated :c:func: Usage 2020-08-11 10:26:08 -06:00
index.rst docs: core-api: avoid using ReST :doc:foo markup 2021-06-17 13:24:37 -06:00
kernel-api.rst kernel.h: split out kstrtox() and simple_strtox() to a separate header 2021-07-01 11:06:05 -07:00
kobject.rst kobject: documentation: Replace HTTP links with HTTPS ones 2020-07-13 09:30:41 -06:00
kref.rst docs: move the kref doc into the core-api book 2020-05-15 12:02:19 -06:00
librs.rst docs-rst: convert librs book to ReST 2017-05-16 08:44:16 -03:00
local_ops.rst timer: Remove init_timer() interface 2017-11-21 15:57:09 -08:00
memory-allocation.rst mm: slab: provide krealloc_array() 2020-12-15 12:13:37 -08:00
memory-hotplug.rst docs/core-api: memory-hotplug: add some details about locking internals 2018-10-12 11:14:19 -06:00
mm-api.rst mm/mmzone.h: fix existing kernel-doc comments and link them to core-api 2021-04-30 11:20:43 -07:00
packing.rst docs: packing: move it to core-api book and adjust markups 2019-07-31 13:30:01 -06:00
padata.rst padata: fold padata_alloc_possible() into padata_alloc() 2020-07-23 17:34:18 +10:00
pin_user_pages.rst selftests/vm: only some gup_test items are really benchmarks 2020-12-15 12:13:38 -08:00
printk-basics.rst Documentation: printk-basics: eliminate duplicated word 2020-07-13 09:44:05 -06:00
printk-formats.rst module: add printk formats to add module build ID to stacktraces 2021-07-08 11:48:22 -07:00
protection-keys.rst x86/Kconfig: Update config and kernel doc for MPK feature on AMD 2020-05-28 18:27:40 +02:00
rbtree.rst docs: rbtree.rst: Fix a typo 2021-03-25 11:38:51 -06:00
refcount-vs-atomic.rst docs: remove :c:func: from refcount-vs-atomic.rst 2019-10-07 09:08:56 -06:00
symbol-namespaces.rst docs/core-api: Consistent code style 2021-05-03 16:52:50 -06:00
this_cpu_ops.rst docs: move other kAPI documents to core-api 2020-06-26 11:33:42 -06:00
timekeeping.rst docs: timekeeping: Use correct prototype for deprecated functions 2020-04-15 14:48:26 -06:00
tracepoint.rst doc: Sphinxify the tracepoint docbook 2016-11-29 14:44:23 -07:00
unaligned-memory-access.rst docs: move other kAPI documents to core-api 2020-06-26 11:33:42 -06:00
workqueue.rst docs: basics.rst: move kernel-doc workqueue markups to workqueue.rst 2020-10-15 07:49:41 +02:00
xarray.rst XArray: add xas_split 2020-10-16 11:11:15 -07:00