From d6f0f22c3c409f9ed88e64f881f8308730be76f0 Mon Sep 17 00:00:00 2001 From: Chris Metcalf <cmetcalf@tilera.com> Date: Thu, 14 Oct 2010 14:42:58 -0400 Subject: [PATCH] arch/tile: update some comments to clarify register usage. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com> --- arch/tile/kernel/intvec_32.S | 2 ++ arch/tile/kernel/process.c | 7 ++++--- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/tile/kernel/intvec_32.S b/arch/tile/kernel/intvec_32.S index 7c7e9ac2580d..c62c2f421ef3 100644 --- a/arch/tile/kernel/intvec_32.S +++ b/arch/tile/kernel/intvec_32.S @@ -1553,6 +1553,8 @@ STD_ENTRY(_sys_clone) * to be available to it on entry. It does not modify any callee-save * registers (including "lr"). It does not check what PL it is being * called at, so you'd better not call it other than at PL0. + * The <atomic.h> wrapper assumes it only clobbers r20-r29, so if + * it ever is necessary to use more registers, be aware. * * It does not use the stack, but since it might be re-interrupted by * a page fault which would assume the stack was valid, it does diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c index 42ff73d5f637..221f12bd27fa 100644 --- a/arch/tile/kernel/process.c +++ b/arch/tile/kernel/process.c @@ -214,9 +214,10 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, /* * Copy the callee-saved registers from the passed pt_regs struct * into the context-switch callee-saved registers area. - * We have to restore the callee-saved registers since we may - * be cloning a userspace task with userspace register state, - * and we won't be unwinding the same kernel frames to restore them. + * This way when we start the interrupt-return sequence, the + * callee-save registers will be correctly in registers, which + * is how we assume the compiler leaves them as we start doing + * the normal return-from-interrupt path after calling C code. * Zero out the C ABI save area to mark the top of the stack. */ ksp = (unsigned long) childregs; -- 2.34.1