Re: [Xen-devel] [PATCH 2/2] build/clang: fix XSM dummy policy when using clang 4.0

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/06/2017 09:54 AM, Jan Beulich wrote:
>>>> On 06.03.17 at 15:42, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> On 03/06/2017 07:52 AM, Jan Beulich wrote:
>>>>>> On 06.03.17 at 13:31, <roger.pau@xxxxxxxxxx> wrote:
>>>> There seems to be some weird bug in clang 4.0 that prevents xsm_pmu_op from
>>>> working as expected, and vpmu.o ends up with a reference to
>>>> __xsm_action_mismatch_detected which makes the build fail:
>>>>
>>>> [...]
>>>> ld    -melf_x86_64_fbsd  -T xen.lds -N prelink.o  \
>>>>     xen/common/symbols-dummy.o -o xen/.xen-syms.0
>>>> prelink.o: In function `xsm_default_action':
>>>> xen/include/xsm/dummy.h:80: undefined reference to 
>>>> `__xsm_action_mismatch_detected'
>>>> xen/xen/include/xsm/dummy.h:80: relocation truncated to fit: R_X86_64_PC32 
>>>> against undefined symbol `__xsm_action_mismatch_detected'
>>>> ld: xen/xen/.xen-syms.0: hidden symbol `__xsm_action_mismatch_detected' 
>>>> isn't defined
>>>>
>>>> Then doing a search in the objects files:
>>>>
>>>> # find xen/ -type f -name '*.o' -print0 | xargs -0 bash -c \
>>>>   'for filename; do nm "$filename" | \
>>>>   grep -q __xsm_action_mismatch_detected && echo "$filename"; done' bash
>>>> xen/arch/x86/prelink.o
>>>> xen/arch/x86/cpu/vpmu.o
>>>> xen/arch/x86/cpu/built_in.o
>>>> xen/arch/x86/built_in.o
>>>>
>>>> The current patch is the only way I've found to fix this so far, by simply
>>>> moving the XSM_PRIV check into the default case in xsm_pmu_op. This also 
>>>> fixes
>>>> the behavior of do_xenpmu_op, which will now return -EINVAL for unknown
>>>> XENPMU_* operations, instead of -EPERM when called by a privileged domain.
>> How will these changes make do_xenpmu_op() return -EINVAL?
> Since the XSM check no longer returns -EPERM, the handling inside
> do_vpmu_op() will now reach the default case there.

Oh, I was staring at xsm_default_action() and trying to see where
-EINVAL would be coming from.

Sorry for the noise.

-boris

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