diff options
| -rw-r--r-- | hw/display/qxl.c | 26 | ||||
| -rw-r--r-- | include/qemu/compiler.h | 9 |
2 files changed, 34 insertions, 1 deletions
diff --git a/hw/display/qxl.c b/hw/display/qxl.c index 747986478f..e628cf1286 100644 --- a/hw/display/qxl.c +++ b/hw/display/qxl.c @@ -1893,7 +1893,31 @@ static void qxl_send_events(PCIQXLDevice *d, uint32_t events) trace_qxl_send_events_vm_stopped(d->id, events); return; } - old_pending = atomic_fetch_or(&d->ram->int_pending, le_events); + /* + * Older versions of Spice forgot to define the QXLRam struct + * with the '__aligned__(4)' attribute. clang 7 and newer will + * thus warn that atomic_fetch_or(&d->ram->int_pending, ...) + * might be a misaligned atomic access, and will generate an + * out-of-line call for it, which results in a link error since + * we don't currently link against libatomic. + * + * In fact we set up d->ram in init_qxl_ram() so it always starts + * at a 4K boundary, so we know that &d->ram->int_pending is + * naturally aligned for a uint32_t. Newer Spice versions + * (with Spice commit beda5ec7a6848be20c0cac2a9a8ef2a41e8069c1) + * will fix the bug directly. To deal with older versions, + * we tell the compiler to assume the address really is aligned. + * Any compiler which cares about the misalignment will have + * __builtin_assume_aligned. + */ +#ifdef HAS_ASSUME_ALIGNED +#define ALIGNED_UINT32_PTR(P) ((uint32_t *)__builtin_assume_aligned(P, 4)) +#else +#define ALIGNED_UINT32_PTR(P) ((uint32_t *)P) +#endif + + old_pending = atomic_fetch_or(ALIGNED_UINT32_PTR(&d->ram->int_pending), + le_events); if ((old_pending & le_events) == le_events) { return; } diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h index 5843812710..bf47e7bee4 100644 --- a/include/qemu/compiler.h +++ b/include/qemu/compiler.h @@ -122,6 +122,15 @@ #ifndef __has_feature #define __has_feature(x) 0 /* compatibility with non-clang compilers */ #endif + +#ifndef __has_builtin +#define __has_builtin(x) 0 /* compatibility with non-clang compilers */ +#endif + +#if __has_builtin(__builtin_assume_aligned) || QEMU_GNUC_PREREQ(4, 7) +#define HAS_ASSUME_ALIGNED +#endif + /* Implement C11 _Generic via GCC builtins. Example: * * QEMU_GENERIC(x, (float, sinf), (long double, sinl), sin) (x) |