On 01.10.2018 18:53, Russell King - ARM Linux wrote:
> On Sun, Sep 30, 2018 at 04:48:20PM -0700, Joe Perches wrote:
>> On Mon, 2018-10-01 at 00:22 +0200, Stefan Agner wrote:
>> > The kernel passes the ArmV6K architecture to the compiler when
>> > using the multi platform selection and enabling ARMv6. Clang
>> > older than version 8.0 emit assembly with an non-existing CPU,
>> > which then makes the assembler fail. Prevent the user from
>> > selecting ARMv6 when using Clang before 8.0.
>> >
>> > Signed-off-by: Stefan Agner <[email protected]>
>> > Link: https://github.com/ClangBuiltLinux/linux/issues/55
>> > ---
>> > arch/arm/Kconfig | 1 +
>> > 1 file changed, 1 insertion(+)
>> >
>> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> > index e8cd55a5b04c..8da160757381 100644
>> > --- a/arch/arm/Kconfig
>> > +++ b/arch/arm/Kconfig
>> > @@ -671,6 +671,7 @@ config ARCH_MULTI_V4_V5
>> >
>> > config ARCH_MULTI_V6
>> > bool "ARMv6 based platforms (ARM11)"
>> > + depends on !CC_IS_CLANG || CLANG_VERSION>=80000
>> > select ARCH_MULTI_V6_V7
>> > select CPU_V6K
>> >
>>
>> Perhaps it'd be better to avoid this in selection
>> criteria in Kconfig and instead add this to
>> include/linux/compiler_clang.h
>> ---
>> include/linux/compiler-clang.h | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
>> index b1ce500fe8b3..90fd16c85359 100644
>> --- a/include/linux/compiler-clang.h
>> +++ b/include/linux/compiler-clang.h
>> @@ -3,6 +3,10 @@
>> #error "Please don't include <linux/compiler-clang.h> directly, include
>> <linux/compiler.h> instead."
>> #endif
>>
>> +#if defined(CONFIG_ARCH_MULTI_V6) && CLANG_VERSION < 80000
>> +# error Sorry, your compiler is too old - please upgrade it.
>> +#endif
>
> (a) does it makes sense to have arch CONFIG_* in linux/*.h? It could
> instead go in arch/arm/kernel/asm-offsets.c, where we have the other
> tests similar to this for GCC.
>
> (b) do we get far enough that the #error will be generated before the
> reported assembler error happens? IOW, would the assembler error
> mask this #error?
>
> I think it needs confirmation that a #error for this problem results
> in the desired behaviour.
Adding the above #error errors out before the assembler error happen in
both cases.
However, adding it to include/linux/compiler-clang.h leads to a bunch of
warnings too:
...
CC kernel/bounds.s
In file included from <built-in>:2:
In file included from ././include/linux/compiler_types.h:59:
./include/linux/compiler-clang.h:7:2: error: "Sorry, your compiler is
too old - please upgrade it."
#error "Sorry, your compiler is too old - please upgrade it."
^
In file included from kernel/bounds.c:10:
In file included from ./include/linux/page-flags.h:10:
In file included from ./include/linux/bug.h:5:
In file included from ./arch/arm/include/asm/bug.h:60:
In file included from ./include/asm-generic/bug.h:18:
In file included from ./include/linux/kernel.h:11:
./include/linux/bitops.h:53:41: warning: shift count >= width of type
[-Wshift-count-overflow]
return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
^~~~~~~~~~~~
./include/asm-generic/bitops/const_hweight.h:29:49: note: expanded from
macro 'hweight64'
#define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) :
__arch_hweight64(w))
^~~~~~~~~~~~~~~~~~~~
./include/asm-generic/bitops/const_hweight.h:21:76: note: expanded from
macro '__const_hweight64'
#define __const_hweight64(w) (__const_hweight32(w) +
__const_hweight32((w) >> 32))
^ ~~
./include/asm-generic/bitops/const_hweight.h:20:49: note: expanded from
macro '__const_hweight32'
#define __const_hweight32(w) (__const_hweight16(w) +
__const_hweight16((w) >> 16))
^
./include/asm-generic/bitops/const_hweight.h:19:48: note: expanded from
macro '__const_hweight16'
#define __const_hweight16(w) (__const_hweight8(w) +
__const_hweight8((w) >> 8 ))
^
./include/asm-generic/bitops/const_hweight.h:10:9: note: expanded from
macro '__const_hweight8'
((!!((w) & (1ULL << 0))) + \
^
Including it to arch/arm/kernel/asm-offsets.c does not lead to those
warnings:
...
CC kernel/bounds.s
UPD include/generated/bounds.h
CC arch/arm/kernel/asm-offsets.s
arch/arm/kernel/asm-offsets.c:51:2: error: "Sorry, your compiler is too
old - please upgrade it."
#error "Sorry, your compiler is too old - please upgrade it."
^
1 error generated.
make[1]: *** [Kbuild:56: arch/arm/kernel/asm-offsets.s] Error 1
make: *** [Makefile:1100: prepare0] Error 2
--
Stefan
