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Adding a line of code to __link_shadow_page() with a literal string
causes a false positive changed function with GCC:
arch/x86/kvm/kvm.ko.o: changed function: kvm_tdp_mmu_map_private_pfn
While the patch only touched __link_shadow_page(), the string addition
triggered a rename of .LC64 -> .LC65 in kvm_tdp_mmu_map_private_pfn()
even though the underlying referenced constant data didn't change.
So for .LC* symbols, the suffix is arbitrary but the data isn't. Add
the underlying data to the checksum calculation rather than the symbol
name.
Clang also uses .LC* symbols, but also uses anonymous data. Both
compilers put this data in .rodata.cst<num> sections.
Fixes: 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums")
Link: https://patch.msgid.link/f3a9e74ceebc6475ce94bcfe985401140857814a.1787939301.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
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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 70589843b36f ("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: 0d83da43b1e1 ("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>
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Start checksumming data objects in preparation for revamping the
correlation algorithm.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
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Move the checksum functionality out of the main objtool command into a
new "objtool klp checksum" subcommand.
This has the benefit of making the code (and the patch generation
process itself) more modular.
For bisectability, both "objtool --checksum" and "objtool klp checksum"
work for now. The former will be removed after klp-build has been
converted to use the new subcommand.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
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Josh Poimboeuf