[PATCH 4.9 08/83] powerpc/boot: Ensure _zimage_start is a weak symbol

Greg Kroah-Hartman
2018-11-19T16:53:42Z

From: Joel Stanley <joel@jms.id.au>

[ Upstream commit ee9d21b3b3583712029a0db65a4b7c081d08d3b3 ]

When building with clang crt0's _zimage_start is not marked weak, which
breaks the build when linking the kernel image:

$ objdump -t arch/powerpc/boot/crt0.o |grep _zimage_start$
0000000000000058 g .text 0000000000000000 _zimage_start

ld: arch/powerpc/boot/wrapper.a(crt0.o): in function '_zimage_start':
(.text+0x58): multiple definition of '_zimage_start';
arch/powerpc/boot/pseries-head.o:(.text+0x0): first defined here

Clang requires the .weak directive to appear after the symbol is
declared. The binutils manual says:

This directive sets the weak attribute on the comma separated list of
symbol names. If the symbols do not already exist, they will be
created.

So it appears this is different with clang. The only reference I could
see for this was an OpenBSD mailing list post[1].

Changing it to be after the declaration fixes building with Clang, and
still works with GCC.

$ objdump -t arch/powerpc/boot/crt0.o |grep _zimage_start$
0000000000000058 w .text 0000000000000000 _zimage_start

Reported to clang as https://bugs.llvm.org/show_bug.cgi?id=38921

[1] https://groups.google.com/forum/#!topic/fa.openbsd.tech/PAgKKen2YCY

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/boot/crt0.S | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/powerpc/boot/crt0.S
+++ b/arch/powerpc/boot/crt0.S
@@ -47,8 +47,10 @@ p_end: .long _end
p_pstack: .long _platform_stack_top
#endif

- .weak _zimage_start
.globl _zimage_start
+ /* Clang appears to require the .weak directive to be after the symbol
+ * is defined. See https://bugs.llvm.org/show_bug.cgi?id=38921 */
+ .weak _zimage_start
_zimage_start:
.globl _zimage_start_lib