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51da9dfb7f
ELFNOTE_START allows callers to specify flags for .pushsection assembler
directives. All callsites but ELF_NOTE use "a" for SHF_ALLOC. For vdso's
that explicitly use ELF_NOTE_START and BUILD_SALT, the same section is
specified twice after preprocessing, once with "a" flag, once without.
Example:
.pushsection .note.Linux, "a", @note ;
.pushsection .note.Linux, "", @note ;
While GNU as allows this ordering, it warns for the opposite ordering,
making these directives position dependent. We'd prefer not to precisely
match this behavior in Clang's integrated assembler. Instead, the non
__ASSEMBLY__ definition of ELF_NOTE uses
__attribute__((section(".note.Linux"))) which is created with SHF_ALLOC,
so let's make the __ASSEMBLY__ definition of ELF_NOTE consistent with C
and just always use "a" flag.
This allows Clang to assemble a working mainline (5.6) kernel via:
$ make CC=clang AS=clang
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/913
Link: http://lkml.kernel.org/r/20200325231250.99205-1-ndesaulniers@google.com
Debugged-by: Ilie Halip <ilie.halip@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
100 lines
3.5 KiB
C
100 lines
3.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_ELFNOTE_H
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#define _LINUX_ELFNOTE_H
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/*
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* Helper macros to generate ELF Note structures, which are put into a
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* PT_NOTE segment of the final vmlinux image. These are useful for
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* including name-value pairs of metadata into the kernel binary (or
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* modules?) for use by external programs.
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*
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* Each note has three parts: a name, a type and a desc. The name is
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* intended to distinguish the note's originator, so it would be a
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* company, project, subsystem, etc; it must be in a suitable form for
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* use in a section name. The type is an integer which is used to tag
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* the data, and is considered to be within the "name" namespace (so
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* "FooCo"'s type 42 is distinct from "BarProj"'s type 42). The
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* "desc" field is the actual data. There are no constraints on the
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* desc field's contents, though typically they're fairly small.
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*
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* All notes from a given NAME are put into a section named
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* .note.NAME. When the kernel image is finally linked, all the notes
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* are packed into a single .notes section, which is mapped into the
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* PT_NOTE segment. Because notes for a given name are grouped into
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* the same section, they'll all be adjacent the output file.
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*
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* This file defines macros for both C and assembler use. Their
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* syntax is slightly different, but they're semantically similar.
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*
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* See the ELF specification for more detail about ELF notes.
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*/
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#ifdef __ASSEMBLER__
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/*
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* Generate a structure with the same shape as Elf{32,64}_Nhdr (which
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* turn out to be the same size and shape), followed by the name and
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* desc data with appropriate padding. The 'desctype' argument is the
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* assembler pseudo op defining the type of the data e.g. .asciz while
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* 'descdata' is the data itself e.g. "hello, world".
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*
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* e.g. ELFNOTE(XYZCo, 42, .asciz, "forty-two")
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* ELFNOTE(XYZCo, 12, .long, 0xdeadbeef)
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*/
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#define ELFNOTE_START(name, type, flags) \
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.pushsection .note.name, flags,@note ; \
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.balign 4 ; \
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.long 2f - 1f /* namesz */ ; \
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.long 4484f - 3f /* descsz */ ; \
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.long type ; \
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1:.asciz #name ; \
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2:.balign 4 ; \
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3:
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#define ELFNOTE_END \
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4484:.balign 4 ; \
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.popsection ;
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#define ELFNOTE(name, type, desc) \
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ELFNOTE_START(name, type, "a") \
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desc ; \
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ELFNOTE_END
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#else /* !__ASSEMBLER__ */
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#include <uapi/linux/elf.h>
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/*
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* Use an anonymous structure which matches the shape of
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* Elf{32,64}_Nhdr, but includes the name and desc data. The size and
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* type of name and desc depend on the macro arguments. "name" must
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* be a literal string, and "desc" must be passed by value. You may
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* only define one note per line, since __LINE__ is used to generate
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* unique symbols.
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*/
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#define _ELFNOTE_PASTE(a,b) a##b
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#define _ELFNOTE(size, name, unique, type, desc) \
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static const struct { \
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struct elf##size##_note _nhdr; \
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unsigned char _name[sizeof(name)] \
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__attribute__((aligned(sizeof(Elf##size##_Word)))); \
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typeof(desc) _desc \
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__attribute__((aligned(sizeof(Elf##size##_Word)))); \
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} _ELFNOTE_PASTE(_note_, unique) \
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__used \
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__attribute__((section(".note." name), \
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aligned(sizeof(Elf##size##_Word)), \
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unused)) = { \
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{ \
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sizeof(name), \
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sizeof(desc), \
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type, \
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}, \
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name, \
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desc \
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}
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#define ELFNOTE(size, name, type, desc) \
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_ELFNOTE(size, name, __LINE__, type, desc)
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#define ELFNOTE32(name, type, desc) ELFNOTE(32, name, type, desc)
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#define ELFNOTE64(name, type, desc) ELFNOTE(64, name, type, desc)
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#endif /* __ASSEMBLER__ */
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#endif /* _LINUX_ELFNOTE_H */
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