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2025-11-21objtool: Record symbol name max lengthAlexandre Chartre1-0/+7
Keep track of the maximum length of symbol names. This will help formatting the code flow between different functions. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-10-alexandre.chartre@oracle.com
2025-11-21objtool: Extract code to validate instruction from the validate branch loopAlexandre Chartre1-181/+205
The code to validate a branch loops through all instructions of the branch and validate each instruction. Move the code to validate an instruction to a separated function. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-9-alexandre.chartre@oracle.com
2025-11-21objtool: Disassemble instruction on warning or backtraceAlexandre Chartre5-14/+58
When an instruction warning (WARN_INSN) or backtrace (BT_INSN) is issued, disassemble the instruction to provide more context. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-8-alexandre.chartre@oracle.com
2025-11-21objtool: Store instruction disassembly resultAlexandre Chartre1-6/+71
When disassembling an instruction store the result instead of directly printing it. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-7-alexandre.chartre@oracle.com
2025-11-21objtool: Print symbol during disassemblyAlexandre Chartre3-9/+143
Print symbols referenced during disassembly instead of just printing raw addresses. Also handle address relocation. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-6-alexandre.chartre@oracle.com
2025-11-21objtool: Disassemble code with libopcodes instead of running objdumpAlexandre Chartre11-72/+238
objtool executes the objdump command to disassemble code. Use libopcodes instead to have more control about the disassembly scope and output. If libopcodes is not present then objtool is built without disassembly support. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-4-alexandre.chartre@oracle.com
2025-11-21objtool: Create disassembly contextAlexandre Chartre4-5/+49
Create a structure to store information for disassembling functions. For now, it is just a wrapper around an objtool file. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-3-alexandre.chartre@oracle.com
2025-11-21objtool: Move disassembly functions to a separated fileAlexandre Chartre4-81/+93
objtool disassembles functions which have warnings. Move the code to do that to a dedicated file. The code is just moved, it is not changed. Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://patch.msgid.link/20251121095340.464045-2-alexandre.chartre@oracle.com
2025-11-21Revert "objtool: Warn on functions with ambiguous -ffunction-sections ↵Josh Poimboeuf2-40/+0
section names" This reverts commit 9c7dc1dd897a1cdcade9566ea4664b03fbabf4a4. The check-function-names.sh script now provides the function name checking functionality for all architectures, making the objtool check redundant. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://patch.msgid.link/c7d549d4de8bd1490d106b99630eea5efc69a4dd.1763669451.git.jpoimboe@kernel.org
2025-11-21objtool: Remove second pass of .cold function correlationJosh Poimboeuf2-23/+3
The .cold function parent/child correlation logic has two passes: one in read_symbols() and one in add_jump_destinations(). The second pass was added with commit cd77849a69cf ("objtool: Fix GCC 8 cold subfunction detection for aliased functions") to ensure that if the parent symbol had aliases then the canonical symbol was chosen as the parent. That solution was rather clunky, not to mention incomplete due to the existence of alternatives and switch tables. Now that we have sym->alias, the canonical alias fix can be done much simpler in the first pass, making the second pass obsolete. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/bdab245a38000a5407f663a031f39e14c67a43d4.1763671318.git.jpoimboe@kernel.org
2025-11-21objtool: Skip non-canonical aliased symbols in add_jump_table_alts()Josh Poimboeuf1-1/+1
If a symbol has aliases, make add_jump_table_alts() skip the non-canonical ones to avoid any surprises. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/169aa17564b9aadb74897945ea74ac2eb70c5b13.1763671318.git.jpoimboe@kernel.org
2025-11-21objtool: Return canonical symbol when aliases exist in symbol finding helpersJosh Poimboeuf1-13/+13
When symbol alias ambiguity exists in the symbol finding helper functions, return the canonical sym->alias, as that's the one which gets used by validate_branch() and elsewhere. This doesn't fix any known issues, just makes the symbol alias behavior more robust. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/450470a4897706af77453ad333e18af5ebab653c.1763671318.git.jpoimboe@kernel.org
2025-11-21objtool: Don't alias undefined symbolsJosh Poimboeuf1-2/+2
Objtool is mistakenly aliasing all undefined symbols. That's obviously wrong, though it has no consequence since objtool happens to only use sym->alias for defined symbols. Fix it regardless. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/bc401173a7717757eee672fc1ca5a20451d77b86.1763671318.git.jpoimboe@kernel.org
2025-11-21objtool: Fix .cold function detection for duplicate symbolsJosh Poimboeuf2-3/+27
The objtool .cold child/parent correlation is done in two phases: first in elf_add_symbol() and later in add_jump_destinations(). The first phase is rather crude and can pick the wrong parent if there are duplicates with the same name. The second phase usually fixes that, but only if the parent has a direct jump to the child. It does *not* work if the only branch from the parent to the child is an alternative or jump table entry. Make the first phase more robust by looking for the parent in the same STT_FILE as the child. Fixes the following objtool warnings in an AutoFDO build with a large CLANG_AUTOFDO_PROFILE profile: vmlinux.o: warning: objtool: rdev_add_key() falls through to next function rdev_add_key.cold() vmlinux.o: warning: objtool: rdev_set_default_key() falls through to next function rdev_set_default_key.cold() Fixes: 13810435b9a7 ("objtool: Support GCC 8's cold subfunctions") Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/82c7b52e40efa75dd10e1c550cc75c1ce10ac2c9.1763671318.git.jpoimboe@kernel.org
2025-11-21objtool: Support Clang AUTOFDO .cold functionsJosh Poimboeuf1-1/+9
AutoFDO enables -fsplit-machine-functions which can move the cold parts of a function to a <func>.cold symbol in a .text.split.<func> section. Unlike GCC, the Clang <func>.cold symbols are not marked STT_FUNC. This confuses objtool in several ways, resulting in warnings like the following: vmlinux.o: warning: objtool: apply_retpolines.cold+0xfc: unsupported instruction in callable function vmlinux.o: warning: objtool: machine_check_poll.cold+0x2e: unsupported instruction in callable function vmlinux.o: warning: objtool: free_deferred_objects.cold+0x1f: relocation to !ENDBR: free_deferred_objects.cold+0x26 vmlinux.o: warning: objtool: rpm_idle.cold+0xe0: relocation to !ENDBR: rpm_idle.cold+0xe7 vmlinux.o: warning: objtool: tcp_rcv_state_process.cold+0x1c: relocation to !ENDBR: tcp_rcv_state_process.cold+0x23 Fix it by marking the .cold symbols as STT_FUNC. Fixes: 2fd65f7afd5a ("AutoFDO: Enable machine function split optimization for AutoFDO") Closes: https://lore.kernel.org/20251103215244.2080638-2-xur@google.com Reported-by: Rong Xu <xur@google.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: xur@google.com Tested-by: xur@google.com Link: https://patch.msgid.link/20a67326f04b2a361c031b56d58e8a803b3c5893.1763671318.git.jpoimboe@kernel.org
2025-11-18objtool: Set minimum xxhash version to 0.8Josh Poimboeuf2-2/+2
XXH3 is only supported starting with xxhash 0.8. Enforce that. Fixes: 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums") Closes: https://lore.kernel.org/SN6PR02MB41579B83CD295C9FEE40EED6D4FCA@SN6PR02MB4157.namprd02.prod.outlook.com Reported-by: Michael Kelley <mhklinux@outlook.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Michael Kelley <mhklinux@outlook.com> Tested-by: Michael Kelley <mhklinux@outlook.com> Link: https://patch.msgid.link/7227c94692a3a51840278744c7af31b4797c6b96.1762990139.git.jpoimboe@kernel.org
2025-11-13objtool: Warn on functions with ambiguous -ffunction-sections section namesJosh Poimboeuf2-0/+40
When compiled with -ffunction-sections, a function named startup() will be placed in .text.startup. However, .text.startup is also used by the compiler for functions with __attribute__((constructor)). That creates an ambiguity for the vmlinux linker script, which needs to differentiate those two cases. Similar naming conflicts exist for functions named exit(), split(), unlikely(), hot() and unknown(). One potential solution would be to use '#ifdef CC_USING_FUNCTION_SECTIONS' to create two distinct implementations of the TEXT_MAIN macro. However, -ffunction-sections can be (and is) enabled or disabled on a per-object basis (for example via ccflags-y or AUTOFDO_PROFILE). So the recently unified TEXT_MAIN macro (commit 1ba9f8979426 ("vmlinux.lds: Unify TEXT_MAIN, DATA_MAIN, and related macros")) is necessary. This means there's no way for the linker script to disambiguate things. Instead, use objtool to warn on any function names whose resulting section names might create ambiguity when the kernel is compiled (in whole or in part) with -ffunction-sections. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: live-patching@vger.kernel.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://patch.msgid.link/65fedea974fe14be487c8867a0b8d0e4a294ce1e.1762991150.git.jpoimboe@kernel.org
2025-11-13Merge tag 'v6.18-rc5' into objtool/core, to pick up fixesIngo Molnar1-3/+7
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2025-11-10tools/objtool: Copy the __cleanup unused variable fix for older clangBorislav Petkov (AMD)1-1/+10
Copy from 54da6a092431 ("locking: Introduce __cleanup() based infrastructure") the bits which mark the variable with a cleanup attribute unused so that my clang 15 can dispose of it properly instead of warning that it is unused which then fails the build due to -Werror. Suggested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Link: https://lore.kernel.org/r/20251031114919.GBaQSiPxZrziOs3RCW@fat_crate.local
2025-11-01objtool: Fix skip_alt_group() for non-alternative STAC/CLACJosh Poimboeuf1-1/+4
If an insn->alt points to a STAC/CLAC instruction, skip_alt_group() assumes it's part of an alternative ("alt group") as opposed to some other kind of "alt" such as an exception fixup. While that assumption may hold true in the current code base, Linus has an out-of-tree patch which breaks that assumption by replacing the STAC/CLAC alternatives with raw STAC/CLAC instructions. Make skip_alt_group() more robust by making sure it's actually an alt group before continuing. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Fixes: 2d12c6fb7875 ("objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC") Closes: https://lore.kernel.org/CAHk-=wi6goUT36sR8GE47_P-aVrd5g38=VTRHpktWARbyE-0ow@mail.gmail.com Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: https://patch.msgid.link/3d22415f7b8e06a64e0873b21f48389290eeaa49.1761767616.git.jpoimboe@kernel.org
2025-10-30objtool: Remove unneeded semicolonChen Ni1-1/+1
Remove unnecessary semicolons reported by Coccinelle/coccicheck and the semantic patch at scripts/coccinelle/misc/semicolon.cocci. Signed-off-by: Chen Ni <nichen@iscas.ac.cn> Link: https://patch.msgid.link/20251020020916.1070369-1-nichen@iscas.ac.cn Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-30x86/smpboot: Mark native_play_dead() as __noreturnThorsten Blum1-0/+1
native_play_dead() ends by calling the non-returning function hlt_play_dead() and therefore also never returns. The !CONFIG_HOTPLUG_CPU stub version of native_play_dead() unconditionally calls BUG() and does not return either. Add the __noreturn attribute to both function definitions and their declaration to document this behavior and to potentially improve compiler optimizations. Remove the obsolete comment, and add native_play_dead() to the objtool's list of __noreturn functions. Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev> Link: https://patch.msgid.link/20251027155107.183136-1-thorsten.blum@linux.dev Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-22objtool: Fix failure when being compiled on x32 systemMikulas Patocka1-2/+2
Fix compilation failure when compiling the kernel with the x32 toolchain. In file included from check.c:16: check.c: In function ¡check_abs_references¢: /usr/src/git/linux-2.6/tools/objtool/include/objtool/warn.h:47:17: error: format ¡%lx¢ expects argument of type ¡long unsigned int¢, but argument 7 has type ¡u64¢ {aka ¡long long unsigned int¢} [-Werror=format=] 47 | "%s%s%s: objtool" extra ": " format "\n", \ | ^~~~~~~~~~~~~~~~~ /usr/src/git/linux-2.6/tools/objtool/include/objtool/warn.h:54:9: note: in expansion of macro ¡___WARN¢ 54 | ___WARN(severity, "", format, ##__VA_ARGS__) | ^~~~~~~ /usr/src/git/linux-2.6/tools/objtool/include/objtool/warn.h:74:27: note: in expansion of macro ¡__WARN¢ 74 | #define WARN(format, ...) __WARN(WARN_STR, format, ##__VA_ARGS__) | ^~~~~~ check.c:4713:33: note: in expansion of macro ¡WARN¢ 4713 | WARN("section %s has absolute relocation at offset 0x%lx", | ^~~~ Fixes: 0d6e4563fc03 ("objtool: Add action to check for absence of absolute relocations") Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Ard Biesheuvel <ardb@kernel.org> Link: https://patch.msgid.link/1ac32fff-2e67-5155-f570-69aad5bf5412@redhat.com
2025-10-22objtool/rust: add one more `noreturn` Rust functionMiguel Ojeda1-0/+1
Between Rust 1.79 and 1.86, under `CONFIG_RUST_KERNEL_DOCTESTS=y`, `objtool` may report: rust/doctests_kernel_generated.o: warning: objtool: rust_doctest_kernel_alloc_kbox_rs_13() falls through to next function rust_doctest_kernel_alloc_kvec_rs_0() (as well as in rust_doctest_kernel_alloc_kvec_rs_0) due to calls to the `noreturn` symbol: core::option::expect_failed from code added in commits 779db37373a3 ("rust: alloc: kvec: implement AsPageIter for VVec") and 671618432f46 ("rust: alloc: kbox: implement AsPageIter for VBox"). Thus add the mangled one to the list so that `objtool` knows it is actually `noreturn`. This can be reproduced as well in other versions by tweaking the code, such as the latest stable Rust (1.90.0). Stable does not have code that triggers this, but it could have it in the future. Downstream forks could too. Thus tag it for backport. See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details. Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Cc: stable@vger.kernel.org # Needed in 6.12.y and later. Link: https://patch.msgid.link/20251020020714.2511718-1-ojeda@kernel.org
2025-10-22objtool/klp: Add the debian-based package name of xxhash to the hintBorislav Petkov (AMD)1-1/+1
Add the debian package name for the devel version of the xxHash package "libxxhash-dev". Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://patch.msgid.link/20251017194732.7713-1-bp@kernel.org
2025-10-16Merge branch 'objtool/core' of ↵Peter Zijlstra31-663/+3607
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.
2025-10-15livepatch/klp-build: Introduce klp-build script for generating livepatch modulesJosh Poimboeuf1-2/+4
Add a klp-build script which automates the generation of a livepatch module from a source .patch file by performing the following steps: - 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'. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Add base objtool support for livepatch modulesJosh Poimboeuf4-7/+53
In preparation for klp-build, enable "classic" objtool to work on livepatch modules: - Avoid duplicate symbol/section warnings for prefix symbols and the .static_call_sites and __mcount_loc sections which may have already been extracted by klp diff. - Add __klp_funcs to the IBT function pointer section whitelist. - Prevent KLP symbols from getting incorrectly classified as cold subfunctions. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Refactor prefix symbol creation codeJosh Poimboeuf3-31/+45
The prefix symbol creation code currently ignores all errors, presumably because some functions don't have the leading NOPs. Shuffle the code around a bit, improve the error handling and document why some errors are ignored. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool/klp: Add post-link subcommand to finalize livepatch modulesJosh Poimboeuf4-1/+174
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>
2025-10-15objtool/klp: Add --debug option to show cloning decisionsJosh Poimboeuf3-0/+99
Add a --debug option to klp diff which prints cloning decisions and an indented dependency tree for all cloned symbols and relocations. This helps visualize which symbols and relocations were included and why. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool/klp: Introduce klp diff subcommand for diffing object filesJosh Poimboeuf16-31/+1909
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>
2025-10-15objtool/klp: Add --debug-checksum=<funcs> to show per-instruction checksumsJosh Poimboeuf6-0/+70
Add a --debug-checksum=<funcs> option to the check subcommand to print the calculated checksum of each instruction in the given functions. This is useful for determining where two versions of a function begin to diverge. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool/klp: Add --checksum option to generate per-function checksumsJosh Poimboeuf9-28/+289
In preparation for the objtool klp diff subcommand, add a command-line option to generate a unique checksum for each function. This will enable detection of functions which have changed between two versions of an object file. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Add annotype() helperJosh Poimboeuf10-16/+18
... for reading annotation types. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Add elf_create_file()Josh Poimboeuf3-4/+147
Add interface to enable the creation of a new ELF file. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Add elf_create_reloc() and elf_init_reloc()Josh Poimboeuf2-14/+165
elf_create_rela_section() is quite limited in that it requires the caller to know how many relocations need to be allocated up front. In preparation for the objtool klp diff subcommand, allow an arbitrary number of relocations to be created and initialized on demand after section creation. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Add elf_create_data()Josh Poimboeuf2-22/+54
In preparation for the objtool klp diff subcommand, refactor elf_add_string() by adding a new elf_add_data() helper which allows the adding of arbitrary data to a section. Make both interfaces global so they can be used by the upcoming klp diff code. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Generalize elf_create_section()Josh Poimboeuf3-52/+75
In preparation for the objtool klp diff subcommand, broaden the elf_create_section() interface to give callers more control and reduce duplication of some subtle setup logic. While at it, make elf_create_rela_section() global so sections can be created by the upcoming klp diff code. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Generalize elf_create_symbol()Josh Poimboeuf2-53/+69
In preparation for the objtool klp diff subcommand, broaden the elf_create_symbol() interface to give callers more control and reduce duplication of some subtle setup logic. While at it, make elf_create_symbol() and elf_create_section_symbol() global so sections can be created by the upcoming klp diff code. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Simplify special symbol handling in elf_update_symbol()Josh Poimboeuf1-3/+2
!sym->sec isn't actually a thing: even STT_UNDEF and other special symbol types belong to NULL section 0. Simplify the initialization of 'shndx' accordingly. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Refactor add_jump_destinations()Josh Poimboeuf2-115/+101
The add_jump_destinations() logic is a bit weird and convoluted after being incrementally tweaked over the years. Refactor it to hopefully be more logical and straightforward. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Reindent check_options[]Josh Poimboeuf1-27/+27
Bring the cmdline check_options[] array back into vertical alignment for better readability. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Resurrect --backup optionJosh Poimboeuf3-16/+16
The --backup option was removed with the following commit: aa8b3e64fd39 ("objtool: Create backup on error and print args") ... which tied the backup functionality to --verbose, and only for warnings/errors. It's a bit inelegant and out of scope to tie that to --verbose. Bring back the old --backup option, but with the new behavior: only on warnings/errors, and print the args to make it easier to recreate. Suggested-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Rename --Werror to --werrorJosh Poimboeuf1-1/+1
The objtool --Werror option name is stylistically inconsistent: halfway between GCC's single-dash capitalized -Werror and objtool's double-dash --lowercase convention, making it unnecessarily hard to remember. Make the 'W' lower case (--werror) for consistency with objtool's other options. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Avoid emptying lists for duplicate sectionsJosh Poimboeuf1-4/+0
When a to-be-created section already exists, there's no point in emptying the various lists if their respective sections already exist. In fact it's better to leave them intact as they might get used later. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Simplify reloc offset calculation in unwind_read_hints()Josh Poimboeuf1-8/+1
Simplify the relocation offset calculation in unwind_read_hints(), similar to other conversions which have already been done. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Mark prefix functionsJosh Poimboeuf3-4/+14
In preparation for the objtool klp diff subcommand, introduce a flag to identify __pfx_*() and __cfi_*() functions in advance so they don't need to be manually identified every time a check is needed. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Fix weak symbol hole detection for .cold functionsJosh Poimboeuf2-42/+45
When ignore_unreachable_insn() looks for weak function holes which jump to their .cold functions, it assumes the parent function comes before the corresponding .cold function in the symbol table. That's not necessarily the case with -ffunction-sections. Mark all the holes beforehand (including .cold functions) so the ordering of the discovery doesn't matter. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2025-10-15objtool: Mark .cold subfunctionsJosh Poimboeuf3-17/+17
Introduce a flag to identify .cold subfunctions so they can be detected easier and faster. Acked-by: Petr Mladek <pmladek@suse.com> Tested-by: Joe Lawrence <joe.lawrence@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
generated by cgit v1.2.3 (git 2.39.0) at 2026-04-27 20:44:04 +0300