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(-)