* [PATCH 0/2] powerpc: Clang build fixes
@ 2018-09-10 8:57 Joel Stanley
2018-09-10 8:57 ` [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang Joel Stanley
2018-09-10 8:57 ` [PATCH 2/2] powerpc/boot: Ensure _zimage_start is a weak symbol Joel Stanley
0 siblings, 2 replies; 5+ messages in thread
From: Joel Stanley @ 2018-09-10 8:57 UTC (permalink / raw)
To: linuxppc-dev, Anton Blanchard
Two fixes to get us closer to building with clang. With a one patch[1]
on top of clang master I can build and boot a powernv kernel:
$ make ARCH=powerpc powernv_defconfig
$ ./scripts/config -e PPC_DISABLE_WERROR -d FTRACE -d BTRFS_FS -d MD_RAID456
$ make CC=/scratch/joel/llvm-build/bin/clang-8 CLANG_TRIPLE=powerpc64le-linux-gnu -j128
$ qemu-system-ppc64 -M powernv -m 3G -nographic -kernel zImage.epapr \
-L ~/skiboot/ -initrd ~/rootfs.cpio.xz
Linux version 4.19.0-rc3-00003-g728b25f26bce (joel@ozrom3) (clang version 8.0.0 (trunk 341773)) #12 SMP Mon Sep 10 17:32:05 ACST 2018
The DISABLE_WERROR is due to clang's -Wduplicate-decl-specifier. Some
macros we have in arch/powerpc/include/asm/uaccess.h warn on 'const
typeof(var)', where as the GCC version doesn't. Anton did fix this a
while ago, but the fix was 'reverted' to resolve some sparse warnings.
I think we should re-apply Anton's patch[2].
[1] https://reviews.llvm.org/D50965
[2] http://git.kernel.org/torvalds/c/b91c1e3e7a6f22a6b898e345b745b6a43273c973
Joel Stanley (2):
powerpc/boot: Fix crt0.S syntax for clang
powerpc/boot: Ensure _zimage_start is a weak symbol
arch/powerpc/boot/crt0.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--
2.17.1
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang
2018-09-10 8:57 [PATCH 0/2] powerpc: Clang build fixes Joel Stanley
@ 2018-09-10 8:57 ` Joel Stanley
2018-09-11 11:32 ` Segher Boessenkool
2018-09-10 8:57 ` [PATCH 2/2] powerpc/boot: Ensure _zimage_start is a weak symbol Joel Stanley
1 sibling, 1 reply; 5+ messages in thread
From: Joel Stanley @ 2018-09-10 8:57 UTC (permalink / raw)
To: linuxppc-dev, Anton Blanchard
Clang's assembler does not like the syntax of the cmpdi:
arch/powerpc/boot/crt0.S:168:22: error: unexpected modifier on variable reference
cmpdi 12,RELACOUNT@l
^
arch/powerpc/boot/crt0.S:168:11: error: unknown operand
cmpdi 12,RELACOUNT@l
^
Enclosing RELACOUNT in () makes it is happy. Tested with GCC 8 and Clang
8 (trunk).
Signed-off-by: Joel Stanley <joel@jms.id.au>
---
arch/powerpc/boot/crt0.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index dcf2f15e6797..ace3f3c64620 100644
--- a/arch/powerpc/boot/crt0.S
+++ b/arch/powerpc/boot/crt0.S
@@ -165,7 +165,7 @@ p_base: mflr r10 /* r10 now points to runtime addr of p_base */
ld r13,8(r11) /* get RELA pointer in r13 */
b 11f
10: addis r12,r12,(-RELACOUNT)@ha
- cmpdi r12,RELACOUNT@l
+ cmpdi r12,(RELACOUNT)@l
bne 11f
ld r8,8(r11) /* get RELACOUNT value in r8 */
11: addi r11,r11,16
--
2.17.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 2/2] powerpc/boot: Ensure _zimage_start is a weak symbol
2018-09-10 8:57 [PATCH 0/2] powerpc: Clang build fixes Joel Stanley
2018-09-10 8:57 ` [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang Joel Stanley
@ 2018-09-10 8:57 ` Joel Stanley
1 sibling, 0 replies; 5+ messages in thread
From: Joel Stanley @ 2018-09-10 8:57 UTC (permalink / raw)
To: linuxppc-dev, Anton Blanchard
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
[1] https://groups.google.com/forum/#!topic/fa.openbsd.tech/PAgKKen2YCY
Signed-off-by: Joel Stanley <joel@jms.id.au>
---
arch/powerpc/boot/crt0.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index ace3f3c64620..41c6d03d6e2d 100644
--- a/arch/powerpc/boot/crt0.S
+++ b/arch/powerpc/boot/crt0.S
@@ -47,8 +47,8 @@ p_end: .long _end
p_pstack: .long _platform_stack_top
#endif
- .weak _zimage_start
.globl _zimage_start
+ .weak _zimage_start
_zimage_start:
.globl _zimage_start_lib
_zimage_start_lib:
--
2.17.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang
2018-09-10 8:57 ` [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang Joel Stanley
@ 2018-09-11 11:32 ` Segher Boessenkool
2018-09-14 2:55 ` Joel Stanley
0 siblings, 1 reply; 5+ messages in thread
From: Segher Boessenkool @ 2018-09-11 11:32 UTC (permalink / raw)
To: Joel Stanley; +Cc: linuxppc-dev, Anton Blanchard
On Mon, Sep 10, 2018 at 06:57:13PM +1000, Joel Stanley wrote:
> Clang's assembler does not like the syntax of the cmpdi:
>
> arch/powerpc/boot/crt0.S:168:22: error: unexpected modifier on variable reference
> cmpdi 12,RELACOUNT@l
> ^
> arch/powerpc/boot/crt0.S:168:11: error: unknown operand
> cmpdi 12,RELACOUNT@l
> ^
> Enclosing RELACOUNT in () makes it is happy. Tested with GCC 8 and Clang
> 8 (trunk).
Is clang going to fix this? You also might want to add a comment that
this is a workaround for that broken assembler.
Segher
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang
2018-09-11 11:32 ` Segher Boessenkool
@ 2018-09-14 2:55 ` Joel Stanley
0 siblings, 0 replies; 5+ messages in thread
From: Joel Stanley @ 2018-09-14 2:55 UTC (permalink / raw)
To: Segher Boessenkool; +Cc: linuxppc-dev, Anton Blanchard
On Tue, 11 Sep 2018 at 21:02, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> On Mon, Sep 10, 2018 at 06:57:13PM +1000, Joel Stanley wrote:
> > Clang's assembler does not like the syntax of the cmpdi:
> >
> > arch/powerpc/boot/crt0.S:168:22: error: unexpected modifier on variable reference
> > cmpdi 12,RELACOUNT@l
> > ^
> > arch/powerpc/boot/crt0.S:168:11: error: unknown operand
> > cmpdi 12,RELACOUNT@l
> > ^
> > Enclosing RELACOUNT in () makes it is happy. Tested with GCC 8 and Clang
> > 8 (trunk).
>
> Is clang going to fix this? You also might want to add a comment that
> this is a workaround for that broken assembler.
I am not sure that we need a comment, it doesn't look too out of place
compared to the other uses of wrapping symbols in ().
I did open a bug against clang though in the hope that they can fix
the behaviour:
https://bugs.llvm.org/show_bug.cgi?id=38945
Cheers,
Joel
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2018-09-14 2:55 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-09-10 8:57 [PATCH 0/2] powerpc: Clang build fixes Joel Stanley
2018-09-10 8:57 ` [PATCH 1/2] powerpc/boot: Fix crt0.S syntax for clang Joel Stanley
2018-09-11 11:32 ` Segher Boessenkool
2018-09-14 2:55 ` Joel Stanley
2018-09-10 8:57 ` [PATCH 2/2] powerpc/boot: Ensure _zimage_start is a weak symbol Joel Stanley
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