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, 5 insertions, 8 deletions

diff --git a/include/linux/elfnote.h b/include/linux/elfnote.h
index 69b136e4dd2b..bb3dcded055f 100644
--- a/include/linux/elfnote.h
+++ b/include/linux/elfnote.h
@@ -60,23 +60,21 @@
 
 #else	/* !__ASSEMBLER__ */
 #include <uapi/linux/elf.h>
+#include <linux/compiler.h>
 /*
  * Use an anonymous structure which matches the shape of
  * Elf{32,64}_Nhdr, but includes the name and desc data.  The size and
  * type of name and desc depend on the macro arguments.  "name" must
- * be a literal string, and "desc" must be passed by value.  You may
- * only define one note per line, since __LINE__ is used to generate
- * unique symbols.
+ * be a literal string, and "desc" must be passed by value.
  */
-#define _ELFNOTE_PASTE(a,b)	a##b
-#define _ELFNOTE(size, name, unique, type, desc)			\
+#define ELFNOTE(size, name, type, desc)					\
 	static const struct {						\
 		struct elf##size##_note _nhdr;				\
 		unsigned char _name[sizeof(name)]			\
 		__attribute__((aligned(sizeof(Elf##size##_Word))));	\
 		typeof(desc) _desc					\
 			     __attribute__((aligned(sizeof(Elf##size##_Word)))); \
-	} _ELFNOTE_PASTE(_note_, unique)				\
+	} __UNIQUE_ID(note)						\
 		__used							\
 		__attribute__((section(".note." name),			\
 			       aligned(sizeof(Elf##size##_Word)),	\
@@ -89,11 +87,10 @@
 		name,							\
 		desc							\
 	}
-#define ELFNOTE(size, name, type, desc)		\
-	_ELFNOTE(size, name, __LINE__, type, desc)
 
 #define ELFNOTE32(name, type, desc) ELFNOTE(32, name, type, desc)
 #define ELFNOTE64(name, type, desc) ELFNOTE(64, name, type, desc)
+
 #endif	/* __ASSEMBLER__ */
 
 #endif /* _LINUX_ELFNOTE_H */