[PATCH 08/14] alpha: use generic syscall exit for new tasks

[Magnus Lindholm]

Move fork and kernel-thread startup into C and use
syscall_exit_to_user_mode() for the return to userspace, retaining the
saved user context for exit work.

This also supplies the child syscall-exit tracepoint for fork, vfork,
clone and clone3.

Signed-off-by: Magnus Lindholm <linmag7@xxxxxxxxx>
---
 arch/alpha/kernel/entry.S   | 23 ++++++++++-------------
 arch/alpha/kernel/process.c | 16 ++++++++++++++++
 arch/alpha/kernel/proto.h   |  6 ++++--
 arch/alpha/kernel/signal.c  |  8 --------
 4 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/arch/alpha/kernel/entry.S b/arch/alpha/kernel/entry.S
index 2233eb6da7065e7d85cbc668a09e565bcfd75a52..5da8c0d17a1d893f59bee1a12f5782276432674d 100644
--- a/arch/alpha/kernel/entry.S
+++ b/arch/alpha/kernel/entry.S
@@ -417,11 +417,11 @@ ret_from_exception:
 	beq	$0, restore_other
 	br	restore_all
 
-ret_to_user_from_exception:
-
-	mov	$sp, $16
+ret_from_fork_common:
+	mov	$17, $16
+	mov	$sp, $17
 	DO_SWITCH_STACK
-	jsr	$26, alpha_exit_to_user_mode
+	jsr	$26, alpha_ret_from_fork
 	ldgp	$gp, 0($26)
 	UNDO_SWITCH_STACK
 	br	restore_all
@@ -548,9 +548,9 @@ alpha_switch_to:
 	.align	4
 	.ent	ret_from_fork
 ret_from_fork:
-	lda	$26, ret_to_user_from_exception
-	mov	$17, $16
-	jmp	$31, schedule_tail
+	mov	$31, $18
+	mov	$31, $19
+	br	$31, ret_from_fork_common
 .end ret_from_fork
 
 /*
@@ -560,10 +560,7 @@ ret_from_fork:
 	.globl	ret_from_kernel_thread
 	.ent	ret_from_kernel_thread
 ret_from_kernel_thread:
-	mov	$17, $16
-	jsr	$26, schedule_tail
-	mov	$9, $27
-	mov	$10, $16
-	jsr	$26, ($9)
-	br	$31, ret_to_user_from_exception
+	mov	$9, $18
+	mov	$10, $19
+	br	$31, ret_from_fork_common
 .end ret_from_kernel_thread
diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index 2182496c535661f399a73400e308c0a7fc6d76f1..c7e6e7b593af10305414ea30f5b944b9d21dd2e2 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -10,6 +10,7 @@
  */
 
 #include <linux/cpu.h>
+#include <linux/entry-common.h>
 #include <linux/errno.h>
 #include <linux/module.h>
 #include <linux/sched.h>
@@ -226,6 +227,21 @@ flush_thread(void)
 	current_thread_info()->pcb.unique = 0;
 }
 
+/* The assembly stub keeps the complete user switch_stack below regs. */
+asmlinkage noinstr void alpha_ret_from_fork(struct task_struct *prev,
+					 struct pt_regs *regs,
+					 int (*fn)(void *), void *fn_arg)
+{
+	instrumentation_begin();
+	schedule_tail(prev);
+	if (fn)
+		fn(fn_arg);
+	instrumentation_end();
+
+	/* A kernel thread may return after a successful kernel_execve(). */
+	syscall_exit_to_user_mode(regs);
+}
+
 /*
  * Copy architecture-specific thread state
  */
diff --git a/arch/alpha/kernel/proto.h b/arch/alpha/kernel/proto.h
index 90af335cd6798ad4039ecc2a3c67505eadbd32a2..c418333d0b89d910ec59d1d57d6bcc0550efc4aa 100644
--- a/arch/alpha/kernel/proto.h
+++ b/arch/alpha/kernel/proto.h
@@ -164,14 +164,16 @@ extern void entDbg(void);
 /* pci.c */
 extern void pcibios_claim_one_bus(struct pci_bus *);
 
+/* process.c */
+extern void alpha_ret_from_fork(struct task_struct *prev, struct pt_regs *regs,
+				int (*fn)(void *), void *fn_arg);
+
 /* ptrace.c */
 extern int ptrace_set_bpt (struct task_struct *child);
 extern int ptrace_cancel_bpt (struct task_struct *child);
 
 /* signal.c */
-extern void alpha_schedule_user_work(void);
 extern void do_signal(struct pt_regs *regs, unsigned long r0, unsigned long r19);
-extern void alpha_exit_to_user_mode(struct pt_regs *regs);
 
 /* syscall.c */
 extern void alpha_syscall(struct pt_regs *regs);
diff --git a/arch/alpha/kernel/signal.c b/arch/alpha/kernel/signal.c
index 244fec20294b81e0c749a07321f917befb62b1a7..e3cb1b50c83d9680032731799b644118b46803bc 100644
--- a/arch/alpha/kernel/signal.c
+++ b/arch/alpha/kernel/signal.c
@@ -538,14 +538,6 @@ do_signal(struct pt_regs *regs, unsigned long r0, unsigned long r19)
 		ptrace_set_bpt(current);	/* re-set breakpoint */
 }
 
-asmlinkage noinstr void alpha_exit_to_user_mode(struct pt_regs *regs)
-{
-	instrumentation_begin();
-	local_irq_disable();
-	instrumentation_end();
-	irqentry_exit_to_user_mode(regs);
-}
-
 void arch_do_signal_or_restart(struct pt_regs *regs)
 {
 	struct thread_info *ti = current_thread_info();
-- 
2.43.0