powerpc: Rearrange copy_thread child stack creation

This makes it a bit clearer where the stack frame is created, and will
allow easier use of some of the stack offset constants in a later
change.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-5-npiggin@gmail.com

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 5265da2d80340e079e12d354030aa8b3f7abecfa..f93703ea4a127d2bf60563ab2b0e8a656f4c623a 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1755,13 +1755,16 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
        klp_init_thread_info(p);
 
+       /* Create initial stack frame. */
+       sp -= (sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD);
+       ((unsigned long *)sp)[0] = 0;
+
        /* Copy registers */
-       sp -= sizeof(struct pt_regs);
-       childregs = (struct pt_regs *) sp;
+       childregs = (struct pt_regs *)(sp + STACK_FRAME_OVERHEAD);
        if (unlikely(args->fn)) {
                /* kernel thread */
                memset(childregs, 0, sizeof(struct pt_regs));
-               childregs->gpr[1] = sp + sizeof(struct pt_regs);
+               childregs->gpr[1] = sp + (sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD);
                /* function */
                if (args->fn)
                        childregs->gpr[14] = ppc_function_entry((void *)args->fn);
@@ -1796,7 +1799,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
                        f = ret_from_fork;
        }
        childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);
-       sp -= STACK_FRAME_OVERHEAD;
 
        /*
         * The way this works is that at some point in the future
@@ -1806,7 +1808,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
         * do some house keeping and then return from the fork or clone
         * system call, using the stack frame created above.
         */
-       ((unsigned long *)sp)[0] = 0;
        sp -= sizeof(struct pt_regs);
        kregs = (struct pt_regs *) sp;
        sp -= STACK_FRAME_OVERHEAD;