elfnote: mark all .note sections SHF_ALLOC

[ Upstream commit 51da9dfb7f20911ae4e79e9b412a9c2d4c373d4b ]

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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Reviewed-by: Fangrui Song <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vincenzo Frascino <[email protected]>
Link: ClangBuiltLinux/linux#913
Link: http://lkml.kernel.org/r/[email protected]
Debugged-by: Ilie Halip <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: nickdesaulniers

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