From: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Date: Tue, 19 Jan 2016 14:14:43 -0800 > On Tue, Jan 19, 2016 at 1:55 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: >> On Tue, Jan 19, 2016 at 01:47:24PM -0800, Andy Lutomirski wrote: >>> Essentially all users of is_compat_task in the kernel are trying to >>> determine whether they are executing in the context of a compat >>> syscall. On at least x86_64 and sparc, these are not at all the >>> same question. >>> >>> On x86_64 and sparc, therefore, is_compat_task doesn't return the >>> overall compat state of the task; it returns true if the task is >>> currently in a compat syscall. >> >> The hell it does. Andy, TIF_32BIT is *NOT* set on syscall entry; it is >> set by execve(). And 64bit task (with that bit clear) can bloody well >> issue 32bit syscalls. Really. > > It does on x86. It does not on sparc. But syscall_get_arch on sparc > *also* doesn't appear to work right. > > davem, how can I check the current syscall bitness on sparc? It's not > obvious to me that it's possible. You have to do it by context if it's important. In addition to the example Al gave, 32-bit processes can make 64-bit syscalls too. GDB and other ptrace() using applications can use this to trace 64-bit programs from 32-bit tracer apps. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
