On 08/11/2023 18.57, Richard Henderson wrote:
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 <th...@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.hender...@linaro.org>
I just noticed that this new type needs to be declared for the #else part,
too, otherwise the compilation breaks with --enable-tcg-interpreter :
diff --git a/include/qemu/int128.h b/include/qemu/int128.h
--- a/include/qemu/int128.h
+++ b/include/qemu/int128.h
@@ -225,6 +225,7 @@ static inline Int128 int128_rems(Int128 a, Int128 b)
#else /* !CONFIG_INT128 */
typedef struct Int128 Int128;
+typedef struct Int128 __attribute__((aligned(16))) Int128Aligned;
/*
* We guarantee that the in-memory byte representation of an
I'll add that when picking up the patch.
Thomas
