Re: [RFC] kallsyms: embed source file:line info in kernel stack traces

Richard Weinberger
2026-03-03T06:26:22Z

----- Ursprüngliche Mail -----
> Von: "Sasha Levin" <sashal@kernel.org>
> 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)
> [ 11.209324] panic+0xc9/0xd0 (kernel/panic.c:787)
> [ 11.211873] ? find_held_lock+0x2b/0x80 (kernel/locking/lockdep.c:5350)
> [ 11.212597] ? lock_release+0xd3/0x300 (kernel/locking/lockdep.c:5535)
> [ 11.213312] sysrq_handle_crash+0x1a/0x20 (drivers/tty/sysrq.c:154)
> [ 11.214005] __handle_sysrq.cold+0x66/0x256 (drivers/tty/sysrq.c:611)
> [ 11.214712] write_sysrq_trigger+0x65/0x80 (drivers/tty/sysrq.c:1221)
> [ 11.215424] proc_reg_write+0x1bd/0x3c0 (fs/proc/inode.c:330)
> [ 11.216061] vfs_write+0x1c6/0xff0 (fs/read_write.c:686)
> [ 11.218848] ksys_write+0xfa/0x200 (fs/read_write.c:740)
> [ 11.222394] do_syscall_64+0xf3/0x690 (arch/x86/entry/syscall_64.c:63)
> [ 11.223942] entry_SYSCALL_64_after_hwframe+0x77/0x7f
> (arch/x86/entry/entry_64.S:121)

Seems useful. :-)

> At build time, a new host tool (scripts/gen_lineinfo) reads DWARF
> .debug_line from vmlinux using libdw (elfutils), extracts all
> address-to-file:line mappings, and generates an assembly file with
> sorted parallel arrays (offsets from _text, file IDs, and line
> numbers). These are linked into vmlinux as .rodata.
>
> At runtime, kallsyms_lookup_lineinfo() does a binary search on the
> table and __sprint_symbol() appends "(file:line)" to each stack frame.
> The lookup uses offsets from _text so it works with KASLR, requires no
> locks or allocations, and is safe in any context including panic.
>
> The feature requires CONFIG_DEBUG_INFO (for DWARF data) and
> elfutils (libdw-dev) on the build host.
>
> Memory footprint measured with a simple KVM guest x86_64 config:
>
> Table: 4,597,583 entries from 4,841 source files
> lineinfo_addrs[] 4,597,583 x u32 = 17.5 MiB
> lineinfo_file_ids[] 4,597,583 x u16 = 8.8 MiB
> lineinfo_lines[] 4,597,583 x u32 = 17.5 MiB
> file_offsets + filenames ~ 0.1 MiB
> Total .rodata increase: ~ 44.0 MiB
>
> vmlinux (stripped): 529 MiB -> 573 MiB (+44 MiB / +8.3%)

Hm, that's a significant increase.

Thanks,
//richard