linux-kernel - [PATCH] elfnote: mark all .note sections SHF

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Date:   Wed, 25 Mar 2020 16:12:49 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jeremy Fitzhardinge <jeremy@...source.com>,
        Ilie Halip <ilie.halip@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] elfnote: mark all .note sections SHF_ALLOC

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

Link: https://github.com/ClangBuiltLinux/linux/issues/913
Cc: Jeremy Fitzhardinge <jeremy@...source.com>
Debugged-by: Ilie Halip <ilie.halip@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Ilie has further treewide cleanups:
https://github.com/ihalip/linux/commits/elfnote
This patch is the simplest to move us forwards.

 include/linux/elfnote.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/elfnote.h b/include/linux/elfnote.h
index 594d4e78654f..69b136e4dd2b 100644
--- a/include/linux/elfnote.h
+++ b/include/linux/elfnote.h
@@ -54,7 +54,7 @@
 .popsection				;

 #define ELFNOTE(name, type, desc)		\
-	ELFNOTE_START(name, type, "")		\
+	ELFNOTE_START(name, type, "a")		\
 		desc			;	\
 	ELFNOTE_END

-- 
2.26.0.rc2.310.g2932bb562d-goog