On Thu, Oct 4, 2012 at 3:48 AM, Al Viro <v...@zeniv.linux.org.uk> wrote: > On Wed, Oct 03, 2012 at 03:23:56PM -0700, Chris Zankel wrote: >> Hi Linus, >> >> Please pull the changes for the Xtensa architecture for v3.7. >> >> Thanks, >> -Chris > > BTW, could you do an xtensa counterpart of the stuff in > git.kernel.org/pub/scm/linux/kernel/git/viro/signal#experimental-kernel_thread?
I will try to do it, thanks for the outline. > Basically, > * switch kernel_thread() away from "syscall in kernel" model; > select GENERIC_KERNEL_THREAD in Kconfig and have copy_thread() check > p->flags & PF_KTHREAD instead of user_mode(regs). If it's true, set the > child up so that it would wake up not in ret_from_fork() but in > ret_from_kernel_thread(), the latter being > schedule_tail(last); > fn(arg); > sys_exit(0); > where fn and arg would be picked from something set by copy_thread() - either > pt_regs or callee-saved registers if your switch_to() deals with those (in > the latter case you'll obviously have then already in place by the time your > newborn kernel thread wakes up). Have the same value for kernel stack pointer > regardless of user_mode. Use 'usp' for fn, 'unused' for arg and expect regs > to be NULL. Kill kernel_thread() in entry.S. > * add ret_from_kernel_execve() that would simply set sp to value > normal for common_exception_return (i.e. what you used to set it when > going into ret_from_kernel_thread()/ret_from_fork()) and branch to said > common_exception_return(). Define __ARCH_WANT_KERNEL_EXECVE in unistd.h > and kill kernel_execve() in entry.S. ret_from_kernel_execve() will get as > its argument task_pt_regs(current), which often spares us some calculations. > * define __ARCH_WANT_SYS_EXECVE in unistd.h, kill xtensa_execve(); > just use sys_execve instead. > * as an optimization, define current_pt_regs() as > (struct pt_regs *)((unsigned long)current_thread_info() + > KERNEL_STACK_SIZE - (XCHAL_NUM_AREGS-16)*4) - 1). I.e. an equivalent of > task_pt_regs(current) without useless work - task_stack_page(current) is > expanded to task_stack_page(current_thread_info()->task), which is > equal to current_thread_info()... > > That would probably allow more glue removal - no more syscalls from the > kernel, for one thing. For another, xtensa_clone() won't need to locate > struct pt_regs * - current_pt_regs() would work just as well and be faster > anyway. The same goes for xtensa_rt_sigreturn() and xtensa_sigaltstack()... -- Thanks. -- Max -- 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/
