Re: linux-next: build failure after merge of the kvm-arm tree

[Joey Gouly]

On Thu, Feb 22, 2024 at 10:03:49PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> After merging the kvm tree, today's linux-next build (arm64 defconfig)
> failed like this:
> 
> In file included from <command-line>:
> In function 'check_res_bits',
>     inlined from 'kvm_sys_reg_table_init' at arch/arm64/kvm/sys_regs.c:4109:2:
> include/linux/compiler_types.h:449:45: error: call to '__compiletime_assert_591' declared with attribute error: BUILD_BUG_ON failed: ID_AA64DFR1_EL1_RES0 != (GENMASK_ULL(63, 0))
>   449 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       |                                             ^
> include/linux/compiler_types.h:430:25: note: in definition of macro '__compiletime_assert'
>   430 |                         prefix ## suffix();                             \
>       |                         ^~~~~~
> include/linux/compiler_types.h:449:9: note: in expansion of macro '_compiletime_assert'
>   449 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       |         ^~~~~~~~~~~~~~~~~~~
> include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
>    39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>       |                                     ^~~~~~~~~~~~~~~~~~
> include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
>    50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>       |         ^~~~~~~~~~~~~~~~
> arch/arm64/kvm/check-res-bits.h:58:9: note: in expansion of macro 'BUILD_BUG_ON'
>    58 |         BUILD_BUG_ON(ID_AA64DFR1_EL1_RES0       != (GENMASK_ULL(63, 0)));
>       |         ^~~~~~~~~~~~
> 
> I bisected this to the merge of the kvm-arm tree into linux-next but I
> could not figure out why it fails :-(
> 
> -- 
> Cheers,
> Stephen Rothwell

This fails because https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=fdd867fe9b32
added new fields to that register (ID_AA64DFR1_EL1)

and commit b80b701d5a6 ("KVM: arm64: Snapshot all non-zero RES0/RES1 sysreg fields for later checking")
took a snapshot of the fields, so the RES0 (reserved 0) bits don't match anymore.

Not sure how to resolve it in the git branches though.

Thanks,
Joey