linux/tools/objtool
Josh Poimboeuf cca84cb129 objtool/klp: Fix position-dependent checksums for non-relocated jumps/calls
When computing klp checksums, instructions with non-relocated jump/call
destination offsets are problematic because the offset values can change
when surrounding code has moved, causing the function to be incorrectly
marked as changed.

Specifically, that includes jumps from alternatives to the end of the
alternative, which from objtool's perspective are jumps to the end of
the alternative instruction block in the original function.

Note that 'jump_dest' jumps don't include sibling calls (those use
call_dest), nor do they include jumps to/from .cold sub functions (those
are cross-section and need a reloc).

Fix it by hashing the opcode bytes (excluding the immediate operand)
along with a position-independent representation of the destination.
For calls, use the function name, and for jumps, use the destination's
offset within its function.

[Note the "9 bit hole" comment was wrong: it has been 8 bits since
commit 70589843b3 ("objtool: Add option to trace function validation")
added the 'trace' field.  Adding the 4-bit 'immediate_len' field now
leaves a 4-bit hole.]

Fixes: 0d83da43b1 ("objtool/klp: Add --checksum option to generate per-function checksums")
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2026-05-04 21:16:06 -07:00
..
arch objtool/klp: Fix position-dependent checksums for non-relocated jumps/calls 2026-05-04 21:16:06 -07:00
Documentation Revert "objtool: Warn on functions with ambiguous -ffunction-sections section names" 2025-11-21 10:04:10 +01:00
include/objtool objtool/klp: Fix position-dependent checksums for non-relocated jumps/calls 2026-05-04 21:16:06 -07:00
.gitignore objtool: Add Function to get the name of a CPU feature 2025-11-24 20:39:47 +01:00
Build objtool/klp: Add "objtool klp checksum" subcommand 2026-05-04 21:16:05 -07:00
builtin-check.c objtool/klp: Remove "objtool --checksum" 2026-05-04 21:16:05 -07:00
builtin-klp.c objtool/klp: Add "objtool klp checksum" subcommand 2026-05-04 21:16:05 -07:00
check.c objtool: Add insn_sym() helper 2026-05-04 21:16:06 -07:00
disas.c objtool: Add insn_sym() helper 2026-05-04 21:16:06 -07:00
elf.c objtool/klp: Don't set sym->file for section symbols 2026-05-04 21:16:04 -07:00
klp-checksum.c objtool/klp: Fix position-dependent checksums for non-relocated jumps/calls 2026-05-04 21:16:06 -07:00
klp-diff.c objtool/klp: Add correlation debugging output 2026-05-04 21:16:06 -07:00
klp-post-link.c objtool/klp: Add post-link subcommand to finalize livepatch modules 2025-10-14 14:50:18 -07:00
Makefile objtool: Include libsubcmd headers directly from source tree 2026-05-04 21:16:04 -07:00
noreturns.h x86/smpboot: Mark native_play_dead() as __noreturn 2025-10-30 08:29:41 -07:00
objtool.c objtool/klp: Add correlation debugging output 2026-05-04 21:16:06 -07:00
orc_dump.c objtool: Add annotype() helper 2025-10-14 14:46:49 -07:00
orc_gen.c objtool: Add annotype() helper 2025-10-14 14:46:49 -07:00
signal.c objtool: Add more robust signal error handling, detect and warn about stack overflows 2025-12-03 19:42:37 +01:00
special.c objtool: Provide access to feature and flags of group alternatives 2025-11-21 15:30:14 +01:00
sync-check.sh objtool/klp: Introduce klp diff subcommand for diffing object files 2025-10-14 14:50:18 -07:00
trace.c objtool: Add insn_sym() helper 2026-05-04 21:16:06 -07:00
weak.c objtool/klp: Introduce klp diff subcommand for diffing object files 2025-10-14 14:50:18 -07:00