This series adds CONFIG_KALLSYMS_LINEINFO, which embeds source file:line information directly in the kernel image so that stack traces annotate every frame with the originating source location - no external tools, no debug symbols at runtime, and safe to use in NMI/panic context.
Motivation ========== The recent "slowly decommission bugzilla?" thread [1] surfaced a recurring problem: when users encounter kernel crashes they see stack traces like `func+0x1ec/0x240` but have no way to identify which subsystem or maintainer to contact. Richard Weinberger proposed building a database mapping symbols to source files using nm/DWARF. Linus pointed to scripts/decode_stacktrace.sh as the existing solution. But as the discussion progressed, it became clear that decode_stacktrace.sh has significant practical barriers that prevent it from being useful in the common case. Problems with scripts/decode_stacktrace.sh ========================================== - Requires debug symbols: the script needs vmlinux with DWARF debug info. Many distros don't retain debug symbols for older or security kernels, and even when available, asking users to obtain matching debuginfo packages is a significant hurdle. - Requires toolchain: users need addr2line and nm installed. - Version-matching requirement: debug symbols must exactly match the running kernel binary. What this series does ===================== Patch 1: CONFIG_KALLSYMS_LINEINFO At build time, a host tool (scripts/gen_lineinfo) reads DWARF .debug_line from vmlinux, extracts address-to-file:line mappings, and embeds them as sorted lookup tables in .rodata. At runtime, kallsyms_lookup_lineinfo() binary-searches the table and __sprint_symbol() appends "(file:line)" to each stack frame. NMI/panic-safe (no locks, no allocations), KASLR-compatible. Patch 2: CONFIG_KALLSYMS_LINEINFO_MODULES Extends lineinfo to loadable modules. Each .ko gets a .mod_lineinfo section embedded at build time. The module loader picks it up at load time. Same zero-allocation, NMI-safe lookup. Patch 3: delta compression Block-indexed delta-encoding with ULEB128 varints, implementing the approach suggested by Juergen Gross in the RFC review. Reduces overhead from ~44 MiB to ~11 MiB (~3.7 bytes/entry), addressing the primary size concern from the RFC. Example output ============== [ 11.206749] dump_stack_lvl+0x5d/0x80 (lib/dump_stack.c:94) [ 11.207403] vpanic+0x36e/0x620 (kernel/panic.c:650) [ 11.209324] panic+0xc9/0xd0 (kernel/panic.c:787) [ 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) Size impact =========== With delta compression, a defconfig+debug x86_64 build adds ~11 MiB to the kernel image (~3.7 bytes per DWARF line entry). This is a fraction of the cost of shipping full DWARF debug info (hundreds of MiB), which distros must store and serve for every kernel version. For distros, maintaining debug symbol repositories is expensive: storage, mirrors, and CDN bandwidth for hundreds of MiB per kernel build add up quickly. An ~11 MiB increase in the kernel image itself is a modest cost that eliminates the need for users to find, download, and version-match debuginfo packages just to make a crash report useful. For developers, the file:line annotations appear immediately in crash traces - no post-processing with decode_stacktrace.sh needed. Changes since RFC ================= - Added module support (patch 2) - Added delta compression (patch 3), reducing size from ~44 MiB to ~11 MiB, addressing the primary concern from RFC review - Added documentation (Documentation/admin-guide/kallsyms-lineinfo.rst) - Added MAINTAINERS entry Link: https://lore.kernel.org/all/[email protected]/ [1] Sasha Levin (3): kallsyms: embed source file:line info in kernel stack traces kallsyms: extend lineinfo to loadable modules kallsyms: delta-compress lineinfo tables for ~2.7x size reduction Documentation/admin-guide/index.rst | 1 + .../admin-guide/kallsyms-lineinfo.rst | 97 +++ MAINTAINERS | 8 + include/linux/kallsyms.h | 32 +- include/linux/mod_lineinfo.h | 137 ++++ include/linux/module.h | 19 + init/Kconfig | 35 + kernel/kallsyms.c | 132 ++++ kernel/kallsyms_internal.h | 11 + kernel/module/kallsyms.c | 156 ++++ kernel/module/main.c | 4 + scripts/.gitignore | 1 + scripts/Makefile | 4 + scripts/Makefile.modfinal | 6 + scripts/gen-mod-lineinfo.sh | 48 ++ scripts/gen_lineinfo.c | 702 ++++++++++++++++++ scripts/kallsyms.c | 17 + scripts/link-vmlinux.sh | 70 +- 18 files changed, 1476 insertions(+), 4 deletions(-) create mode 100644 Documentation/admin-guide/kallsyms-lineinfo.rst create mode 100644 include/linux/mod_lineinfo.h create mode 100755 scripts/gen-mod-lineinfo.sh create mode 100644 scripts/gen_lineinfo.c -- 2.51.0
