On Fri, Nov 07, 2014 at 12:44:07PM +0000, Arnd Bergmann wrote: > On Friday 07 November 2014 12:11:19 Russell King - ARM Linux wrote: > > On Fri, Nov 07, 2014 at 01:03:00PM +0100, Arnd Bergmann wrote: > > > On Friday 07 November 2014 11:55:51 Will Deacon wrote: > > > > We need this for arm64 and, since all architectures seem to have a > > > > mechanism > > > > for setting a system call via ptrace, moving it to generic code should > > > > make > > > > sense for new architectures too, no? > > > > > > It makes a little more sense now, but I still don't understand why you > > > need to set the system call number via ptrace. What is this used for, > > > and why doesn't any other architecture have this? > > > > All other architectures have a way. x86, for example, you set orig_eax > > (or orig_rax) to change the syscall number. On ARM, that doesn't work > > because we don't always pass the syscall number in a register. > > > > Sorry for being slow today, but why can't we use the same interface that > s390 has on arm64: > > static int s390_system_call_get(struct task_struct *target, > const struct user_regset *regset, > unsigned int pos, unsigned int count, > void *kbuf, void __user *ubuf) > { > unsigned int *data = &task_thread_info(target)->system_call; > return user_regset_copyout(&pos, &count, &kbuf, &ubuf, > data, 0, sizeof(unsigned int)); > } > > static int s390_system_call_set(struct task_struct *target, > const struct user_regset *regset, > unsigned int pos, unsigned int count, > const void *kbuf, const void __user *ubuf) > { > unsigned int *data = &task_thread_info(target)->system_call; > return user_regset_copyin(&pos, &count, &kbuf, &ubuf, > data, 0, sizeof(unsigned int)); > } > > static const struct user_regset s390_regsets[] = { > ... > { > .core_note_type = NT_S390_SYSTEM_CALL, > .n = 1, > .size = sizeof(unsigned int), > .align = sizeof(unsigned int), > .get = s390_system_call_get, > .set = s390_system_call_set, > }, > ... > }; > > Is it just preference for being consistent with ARM32, or is there a > reason this won't work?
Interesting, I hadn't considered a unit-length regset. > It's not that I care strongly about the interface, my main point is > that the changelog doesn't describe why one interface was used instead > the other. I suspect the current approach was taken because it follows the same scheme as 32-bit ARM. If both methods are sufficient (Kees would have a better idea than me on that), then I don't have a strong preference. Will -- 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/