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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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