Re: [PATCH] host/include/generic/host/atomic128: Fix compilation problem with Clang 17

[Richard Henderson <richard.henderson@linaro.org>]

On 11/8/23 00:59, Thomas Huth wrote:
> When compiling QEMU with Clang 17 on a s390x, the compilation fails:
> 
> In file included from ../accel/tcg/cputlb.c:32:
> In file included from /root/qemu/include/exec/helper-proto-common.h:10:
> In file included from /root/qemu/include/qemu/atomic128.h:62:
> /root/qemu/host/include/generic/host/atomic128-ldst.h:68:15: error:
>   __sync builtin operation MUST have natural alignment (consider using __
> atomic). [-Werror,-Wsync-alignment]
>     68 |     } while (!__sync_bool_compare_and_swap_16(ptr_align, old, new.i));
>        |               ^
> In file included from ../accel/tcg/cputlb.c:32:
> In file included from /root/qemu/include/exec/helper-proto-common.h:10:
> In file included from /root/qemu/include/qemu/atomic128.h:61:
> /root/qemu/host/include/generic/host/atomic128-cas.h:36:11: error:
>   __sync builtin operation MUST have natural alignment (consider using __a
> tomic). [-Werror,-Wsync-alignment]
>     36 |     r.i = __sync_val_compare_and_swap_16(ptr_align, c.i, n.i);
>        |           ^
> 2 errors generated.
> 
> It's arguably a bug in Clang since we already use __builtin_assume_aligned()
> to tell the compiler that the pointer is properly aligned. But according to
> https://github.com/llvm/llvm-project/issues/69146 it seems like the Clang
> folks don't see an easy fix on their side and recommend to use a type
> declared with __attribute__((aligned(16))) to work around this problem.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1934
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   host/include/generic/host/atomic128-cas.h  | 2 +-
>   host/include/generic/host/atomic128-ldst.h | 2 +-
>   include/qemu/int128.h                      | 1 +
>   3 files changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~