On Mon, Oct 24, 2016 at 08:13:22PM -0700, Richard Henderson wrote: > On 10/24/2016 01:59 PM, Helge Deller wrote: > > Does it only happens for __copy_user() ? > > If yes, I assume the problem happens because of __copy_tofrom_user_nocheck() in > > uaccess.h is always inlined. Maybe un-inlining helps? > > Or, the inline-assembly for jsr/bsr needs tweeking ? > > Indeed. Try changing #ifdef MODULE above __copy_tofrom_user_nocheck to #if 1. Thanks, that indeed fixes it. While I have your ears (or eyes since this is email) I have been running the ltp tests and noted some syscall test failures. The sendmsg call fails with a segfault instead of returning EFAULT, when one passes in a NULL for the message arg. When the test is run under gdb it reports the segfault in the libc sendmsg function at the instruction immediately following the syscall instruction and that instruction is a move of a register to another register, not a memory access. Would I be correct in surmising that the segfault actually occurred in kernel code but gets reported at the instruction following the syscall instruction in user space? (But looking at the kernel source for sys_sendmsg it looks to me that the msg argument is properly checked before being accessed so why a segfault should occur is not obvious...) (I see fstatfs also segfaults when passed a bad pointer but that's because libc does not pass the bad address to the kernel, but passes the address of a temporary buffer from which libc then copies back into the bad address, thus kaboom instead of EFAULT. C'est la vie.) And while I mention gdb, it no longer works on Alpha since version 7.10. Richard, would you be able to take a look at the bug report: https://sourceware.org/bugzilla/show_bug.cgi?id=19061 And while I mention libc I am seeing (rather rare) random segfaults in programs such as cp, tar, install and dpkg ever since the upgrade to glibc 2.23 (or maybe it was 2.24). I am struggling to get a backtrace because it only happens very occassionally (but often enough that it is almost impossible for a build and install of large software packages such as libreoffice to complete without failure at some random point) and when I rerun the failing program manually it then always works. I'll keep trying to narrow this one down. Cheers Michael. -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
