On Mon, Mar 28, 2011 at 12:19:39PM +0000, Chen Jie wrote: > Hi all, Hi, > In an o32 user land + n64 kernel, calling 'fanotify_mark' indirectly > will always fail due to alignment[1]: > syscall(_NR_fanotify_mark, fanotify_fd, flags, mask, dfd, pathname) > > The prototype of fanotify_mark is "fanotify_mark (int fanotify_fd, > unsigned int flags, __u64 mask, int dfd, const char __user * > pathname)", which has a 64bit argument. > > In the case of o32 user land + n64 kernel and indirect syscall: > 1. User calls libc routine syscall(...), MIPS ABI enforce a padding > word before argument 'mask' to make it 64bit-aligned. The padding word > resides at a3 register. > 2. Kernel fetches 4 32bit arguments from a0-a3, and then 4 32bit > arguments from stack. > 3. Kernel shifts arguments by one, then redirects to sys_32_fanotify_mark. > 4. sys_32_fanotify_mark synthesizes the 64bit argument 'mask' by > merge_64(a2, a3), note a2 is the padding word, so the synthesized > argument is invalid. > > The syscall routine in libc doesn't know the prototype, so it can't do > anything. It seems the bug of syscall handling code, any idea? > I can confirm the issue, however it is not specific to a n64 kernel. Even with an o32 kernel the issue is present. I also have been able to reproduce the issue on other architectures, like PowerPC. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurelien@xxxxxxxxxxx http://www.aurel32.net
