On Sun, Jan 26, 2014 at 02:28:15PM -0800, Linus Torvalds wrote: > The x86-64 (and 32-bit, for that matter) system call slowpaths are all > in C, but the *selection* of which slow-path to take is a mixture of > complicated assembler ("sysret_check -> sysret_careful -> > sysret_signal ->sysret_audit -> int_check_syscall_exit_work" etc), and > oddly named and placed C code ("schedule_user" vs > "__audit_syscall_exit" vs "do_notify_resume"). > > This attached patch tries to take the "do_notify_resume()" approach, > and renaming it to something sane ("syscall_exit_slowpath") and call > out to *all* the different slow cases from that one place, instead of > having some cases hardcoded in asm, and some in C. And instead of > hardcoding which cases result in a "iretq" and which cases result in a > faster sysret case, it's now simply a return value from that > syscall_exit_slowpath() function, so it's very natural and easy to say > "taking a signal will force us to do the slow iretq case, but we can > do the task exit work and still do the sysret". > > I've marked this as an RFC, because I didn't bother trying to clean up > the 32-bit code similarly (no test-cases, and trust me, if you get > this wrong, it will fail spectacularly but in very subtle and > hard-to-debug ways), and I also didn't bother with the slow cases in > the "iretq" path, so that path still has the odd asm cases and calls > the old (now legacy) do_notify_resume() path.
Umm... Can't uprobe_notify_resume() modify regs as well? While we are at it, when we start using the same thing on 32bit kernels, we'll need to watch out for execve() - the reason why start_thread() sets TIF_NOTIFY_RESUME is to force us away from sysexit path. IIRC, vm86 is another thing to watch out for (same reasons). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/