Merge tag 'objtool-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool updates from Ingo Molnar:

- klp-build livepatch module generation (Josh Poimboeuf)

Int

Merge tag 'objtool-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool updates from Ingo Molnar:

- klp-build livepatch module generation (Josh Poimboeuf)

Introduce new objtool features and a klp-build script to generate
livepatch modules using a source .patch as input.

This builds on concepts from the longstanding out-of-tree kpatch
project which began in 2012 and has been used for many years to
generate livepatch modules for production kernels. However, this is a
complete rewrite which incorporates hard-earned lessons from 12+
years of maintaining kpatch.

Key improvements compared to kpatch-build:

- Integrated with objtool: Leverages objtool's existing control-flow
graph analysis to help detect changed functions.

- Works on vmlinux.o: Supports late-linked objects, making it
compatible with LTO, IBT, and similar.

- Simplified code base: ~3k fewer lines of code.

- Upstream: No more out-of-tree #ifdef hacks, far less cruft.

- Cleaner internals: Vastly simplified logic for
symbol/section/reloc inclusion and special section extraction.

- Robust __LINE__ macro handling: Avoids false positive binary diffs
caused by the __LINE__ macro by introducing a fix-patch-lines
script which injects #line directives into the source .patch to
preserve the original line numbers at compile time.

- Disassemble code with libopcodes instead of running objdump
(Alexandre Chartre)

- Disassemble support (-d option to objtool) by Alexandre Chartre,
which supports the decoding of various Linux kernel code generation
specials such as alternatives:

17ef: sched_balance_find_dst_group+0x62f mov 0x34(%r9),%edx
17f3: sched_balance_find_dst_group+0x633 | <alternative.17f3> | X86_FEATURE_POPCNT
17f3: sched_balance_find_dst_group+0x633 | call 0x17f8 <__sw_hweight64> | popcnt %rdi,%rax
17f8: sched_balance_find_dst_group+0x638 cmp %eax,%edx

... jump table alternatives:

1895: sched_use_asym_prio+0x5 test $0x8,%ch
1898: sched_use_asym_prio+0x8 je 0x18a9 <sched_use_asym_prio+0x19>
189a: sched_use_asym_prio+0xa | <jump_table.189a> | JUMP
189a: sched_use_asym_prio+0xa | jmp 0x18ae <sched_use_asym_prio+0x1e> | nop2
189c: sched_use_asym_prio+0xc mov $0x1,%eax
18a1: sched_use_asym_prio+0x11 and $0x80,%ecx

... exception table alternatives:

native_read_msr:
5b80: native_read_msr+0x0 mov %edi,%ecx
5b82: native_read_msr+0x2 | <ex_table.5b82> | EXCEPTION
5b82: native_read_msr+0x2 | rdmsr | resume at 0x5b84 <native_read_msr+0x4>
5b84: native_read_msr+0x4 shl $0x20,%rdx

.... x86 feature flag decoding (also see the X86_FEATURE_POPCNT
example in sched_balance_find_dst_group() above):

2faaf: start_thread_common.constprop.0+0x1f jne 0x2fba4 <start_thread_common.constprop.0+0x114>
2fab5: start_thread_common.constprop.0+0x25 | <alternative.2fab5> | X86_FEATURE_ALWAYS | X86_BUG_NULL_SEG
2fab5: start_thread_common.constprop.0+0x25 | jmp 0x2faba <.altinstr_aux+0x2f4> | jmp 0x4b0 <start_thread_common.constprop.0+0x3f> | nop5
2faba: start_thread_common.constprop.0+0x2a mov $0x2b,%eax

... NOP sequence shortening:

1048e2: snapshot_write_finalize+0xc2 je 0x104917 <snapshot_write_finalize+0xf7>
1048e4: snapshot_write_finalize+0xc4 nop6
1048ea: snapshot_write_finalize+0xca nop11
1048f5: snapshot_write_finalize+0xd5 nop11
104900: snapshot_write_finalize+0xe0 mov %rax,%rcx
104903: snapshot_write_finalize+0xe3 mov 0x10(%rdx),%rax

... and much more.

- Function validation tracing support (Alexandre Chartre)

- Various -ffunction-sections fixes (Josh Poimboeuf)

- Clang AutoFDO (Automated Feedback-Directed Optimizations) support
(Josh Poimboeuf)

- Misc fixes and cleanups (Borislav Petkov, Chen Ni, Dylan Hatch, Ingo
Molnar, John Wang, Josh Poimboeuf, Pankaj Raghav, Peter Zijlstra,
Thorsten Blum)

* tag 'objtool-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (129 commits)
objtool: Fix segfault on unknown alternatives
objtool: Build with disassembly can fail when including bdf.h
objtool: Trim trailing NOPs in alternative
objtool: Add wide output for disassembly
objtool: Compact output for alternatives with one instruction
objtool: Improve naming of group alternatives
objtool: Add Function to get the name of a CPU feature
objtool: Provide access to feature and flags of group alternatives
objtool: Fix address references in alternatives
objtool: Disassemble jump table alternatives
objtool: Disassemble exception table alternatives
objtool: Print addresses with alternative instructions
objtool: Disassemble group alternatives
objtool: Print headers for alternatives
objtool: Preserve alternatives order
objtool: Add the --disas=<function-pattern> action
objtool: Do not validate IBT for .return_sites and .call_sites
objtool: Improve tracing of alternative instructions
objtool: Add functions to better name alternatives
objtool: Identify the different types of alternatives
...

show more ...

Merge branch 'objtool/core'

Bring in the UDB and objtool data annotations to avoid conflicts while further extending the bug exceptions.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>

Merge branch 'objtool/core' of https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux

This series introduces new objtool features and a klp-build script to
generate livepatch modules using a

Merge branch 'objtool/core' of https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux

This series introduces new objtool features and a klp-build script to
generate livepatch modules using a source .patch as input.

This builds on concepts from the longstanding out-of-tree kpatch [1]
project which began in 2012 and has been used for many years to generate
livepatch modules for production kernels. However, this is a complete
rewrite which incorporates hard-earned lessons from 12+ years of
maintaining kpatch.

Key improvements compared to kpatch-build:

- Integrated with objtool: Leverages objtool's existing control-flow
graph analysis to help detect changed functions.

- Works on vmlinux.o: Supports late-linked objects, making it
compatible with LTO, IBT, and similar.

- Simplified code base: ~3k fewer lines of code.

- Upstream: No more out-of-tree #ifdef hacks, far less cruft.

- Cleaner internals: Vastly simplified logic for symbol/section/reloc
inclusion and special section extraction.

- Robust __LINE__ macro handling: Avoids false positive binary diffs
caused by the __LINE__ macro by introducing a fix-patch-lines script
which injects #line directives into the source .patch to preserve
the original line numbers at compile time.

The primary user interface is the klp-build script which does the
following:

- Builds an original kernel with -function-sections and
-fdata-sections, plus objtool function checksumming.

- Applies the .patch file and rebuilds the kernel using the same
options.

- Runs 'objtool klp diff' to detect changed functions and generate
intermediate binary diff objects.

- Builds a kernel module which links the diff objects with some
livepatch module init code (scripts/livepatch/init.c).

- Finalizes the livepatch module (aka work around linker wreckage)
using 'objtool klp post-link'.

I've tested with a variety of patches on defconfig and Fedora-config
kernels with both GCC and Clang.

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objtool/klp: Add post-link subcommand to finalize livepatch modules

Livepatch needs some ELF magic which linkers don't like:

- Two relocation sections (.rela*, .klp.rela*) for the same text
s

objtool/klp: Add post-link subcommand to finalize livepatch modules

Livepatch needs some ELF magic which linkers don't like:

- Two relocation sections (.rela*, .klp.rela*) for the same text
section.

- Use of SHN_LIVEPATCH to mark livepatch symbols.

Unfortunately linkers tend to mangle such things. To work around that,
klp diff generates a linker-compliant intermediate binary which encodes
the relevant KLP section/reloc/symbol metadata.

After module linking, the .ko then needs to be converted to an actual
livepatch module. Introduce a new klp post-link subcommand to do so.

Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

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objtool/klp: Introduce klp diff subcommand for diffing object files

Add a new klp diff subcommand which performs a binary diff between two
object files and extracts changed functions into a new obje

objtool/klp: Introduce klp diff subcommand for diffing object files

Add a new klp diff subcommand which performs a binary diff between two
object files and extracts changed functions into a new object which can
then be linked into a livepatch module.

This builds on concepts from the longstanding out-of-tree kpatch [1]
project which began in 2012 and has been used for many years to generate
livepatch modules for production kernels. However, this is a complete
rewrite which incorporates hard-earned lessons from 12+ years of
maintaining kpatch.

Key improvements compared to kpatch-build:

- Integrated with objtool: Leverages objtool's existing control-flow
graph analysis to help detect changed functions.

- Works on vmlinux.o: Supports late-linked objects, making it
compatible with LTO, IBT, and similar.

- Simplified code base: ~3k fewer lines of code.

- Upstream: No more out-of-tree #ifdef hacks, far less cruft.

- Cleaner internals: Vastly simplified logic for symbol/section/reloc
inclusion and special section extraction.

- Robust __LINE__ macro handling: Avoids false positive binary diffs
caused by the __LINE__ macro by introducing a fix-patch-lines script
(coming in a later patch) which injects #line directives into the
source .patch to preserve the original line numbers at compile time.

Note the end result of this subcommand is not yet functionally complete.
Livepatch needs some ELF magic which linkers don't like:

- Two relocation sections (.rela*, .klp.rela*) for the same text
section.

- Use of SHN_LIVEPATCH to mark livepatch symbols.

Unfortunately linkers tend to mangle such things. To work around that,
klp diff generates a linker-compliant intermediate binary which encodes
the relevant KLP section/reloc/symbol metadata.

After module linking, a klp post-link step (coming soon) will clean up
the mess and convert the linked .ko into a fully compliant livepatch
module.

Note this subcommand requires the diffed binaries to have been compiled
with -ffunction-sections and -fdata-sections, and processed with
'objtool --checksum'. Those constraints will be handled by a klp-build
script introduced in a later patch.

Without '-ffunction-sections -fdata-sections', reliable object diffing
would be infeasible due to toolchain limitations:

- For intra-file+intra-section references, the compiler might
occasionally generated hard-coded instruction offsets instead of
relocations.

- Section-symbol-based references can be ambiguous:

- Overlapping or zero-length symbols create ambiguity as to which
symbol is being referenced.

- A reference to the end of a symbol (e.g., checking array bounds)
can be misinterpreted as a reference to the next symbol, or vice
versa.

A potential future alternative to '-ffunction-sections -fdata-sections'
would be to introduce a toolchain option that forces symbol-based
(non-section) relocations.

Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

show more ...