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

[Richard Weinberger <richard@nod.at>]

----- 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