Re: [PATCH v2 1/4] kallsyms: embed source file:line info in kernel stack traces

[Sasha Levin <sashal@kernel.org>]

On Sat, Mar 07, 2026 at 10:41:20PM +0100, Helge Deller wrote:
>Hi Sasha,
>
>On 3/7/26 18:20, Sasha Levin wrote:
>>Add CONFIG_KALLSYMS_LINEINFO, which embeds a compact address-to-line
>>lookup table in the kernel image so stack traces directly print source
>>file and line number information:
>>
>>   root@localhost:~# echo c > /proc/sysrq-trigger
>>   [   11.201987] sysrq: Trigger a crash
>>   [   11.202831] Kernel panic - not syncing: sysrq triggered crash
>>   [   11.206218] Call Trace:
>>   [   11.206501]  <TASK>
>>   [   11.206749]  dump_stack_lvl+0x5d/0x80 (lib/dump_stack.c:94)
>>   [   11.207403]  vpanic+0x36e/0x620 (kernel/panic.c:650)
>>   [   11.208565]  ? __lock_acquire+0x465/0x2240 (kernel/locking/lockdep.c:4674)
>>[...]
>>
>>Assisted-by: Claude:claude-opus-4-6
>>Signed-off-by: Sasha Levin <sashal@kernel.org>
>
>Shows relative paths and works OK on 32- and 64-bit parisc kernel.
>You may add
>Tested-by: Helge Deller <deller@gmx.de>

Thanks for testing! I'm happy the regression was fixed.

>A few notes/suggestions below....
>
>
>>---
>>  Documentation/admin-guide/index.rst           |   1 +
>>  .../admin-guide/kallsyms-lineinfo.rst         |  72 +++
>>  MAINTAINERS                                   |   6 +
>>  include/linux/kallsyms.h                      |  32 +-
>>  init/Kconfig                                  |  20 +
>>  kernel/kallsyms.c                             |  61 +++
>>  kernel/kallsyms_internal.h                    |  11 +
>>  scripts/.gitignore                            |   1 +
>>  scripts/Makefile                              |   3 +
>>  scripts/gen_lineinfo.c                        | 510 ++++++++++++++++++
>>  scripts/kallsyms.c                            |  16 +
>>  scripts/link-vmlinux.sh                       |  70 ++-
>>  12 files changed, 799 insertions(+), 4 deletions(-)
>>  create mode 100644 Documentation/admin-guide/kallsyms-lineinfo.rst
>>  create mode 100644 scripts/gen_lineinfo.c
>
>>diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
>>index aec2f06858afd..c94d8f332c5df 100644
>>--- a/kernel/kallsyms.c
>>+++ b/kernel/kallsyms.c
>>@@ -467,6 +467,54 @@ static int append_buildid(char *buffer,   const char *modname,
>>  #endif /* CONFIG_STACKTRACE_BUILD_ID */
>>+#ifdef CONFIG_KALLSYMS_LINEINFO
>>+bool kallsyms_lookup_lineinfo(unsigned long addr, unsigned long sym_start,
>>+			      const char **file, unsigned int *line)
>>+{
>>+	unsigned long long raw_offset;
>>+	unsigned int offset, low, high, mid, file_id;
>>+
>>+	if (!lineinfo_num_entries)
>>+		return false;
>
>The "#ifdef CONFIG_KALLSYMS_LINEINFO" above prevents that this function
>is compiled when the option is disabled.
>
>Instead, you *could* move the "CONFIG_KALLSYMS_LINEINFO" option into
>the function with "IS_ENABLED()", like this...:
>+	if (!IS_ENABLED(CONFIG_KALLSYMS_LINEINFO) || !lineinfo_num_entries)
>+		return false;
>
>That way your code will always be compiled, and the code will be optimized
>away by the compiler if the option is disabled. The huge benefit is, that
>the compiler will do syntax-checking at every build, so you will see coding
>bugs early.
>
>You could use the same semantic at other places in your patches, and of
>course you then need to remove the #ifdef ...

Ack, this makes sense. I'll do it in the v3 if it's needed.

-- 
Thanks,
Sasha