It turns out that SPARC hosts impose a requirement that if you mmap MAP_SHARED|MAP_FIXED then the address must be aligned to SHMLBA alignment, which for SPARC is 16K and larger than the 8K page size: http://lxr.linux.no/#linux+v4.10.1/arch/sparc/kernel/sys_sparc_64.c#L158
QEMU doesn't really cope with this. In particular, ivmshm doesn't work: $ ppc64-softmmu/qemu-system-ppc64 -display none -device ivshmem,shm=/qtest-20273-1334572184,size=0x1 qemu-system-ppc64: System page size 0x2000 is not enabled in page_size_mask (0x11000). Performance may be slow qemu-system-ppc64: -device ivshmem,shm=/qtest-20273-1334572184,size=0x1: ivshmem is deprecated, please use ivshmem-plain or ivshmem-doorbell instead Unexpected error in file_ram_alloc() at /home/pm215/qemu/exec.c:1599: qemu-system-ppc64: -device ivshmem,shm=/qtest-20273-1334572184,size=0x1: unable to map backing store for guest RAM: Invalid argument Aborted (noticed because this is a make check failure). exec.c calls qemu_fd_getpagesize() to figure out the alignment here (on a file in /dev/shm/) and ends up in its default codepath that returns getpagesize(), which is too small. What's the best way to fix this? As far as I can tell the restriction applies to any mapping, not just /dev/shm files. QEMU's assumptions that pagesize is the alignment requirement seem fairly widespread :-( thanks -- PMM
