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.

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 5b45ea7dff3e..ab181d87d71d 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -163,7 +163,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	__asm__ ("" : "=r" (var) : "0" (var))
 #endif
 
-#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
+/* Format: __UNIQUE_ID_<name>_<__COUNTER__> */
+#define __UNIQUE_ID(name)					\
+	__PASTE(__UNIQUE_ID_,					\
+	__PASTE(name,						\
+	__PASTE(_, __COUNTER__)))
 
 /**
  * data_race - mark an expression as containing intentional data races
@@ -283,7 +287,7 @@ static inline void *offset_to_ptr(const int *off)
  */
 #define ___ADDRESSABLE(sym, __attrs)						\
 	static void * __used __attrs						\
-	__UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)(uintptr_t)&sym;
+	__UNIQUE_ID(__PASTE(addressable_, sym)) = (void *)(uintptr_t)&sym;
 
 #define __ADDRESSABLE(sym) \
 	___ADDRESSABLE(sym, __section(".discard.addressable"))