[PATCH v1] m68k: save extra registers on sys_exit and sys_exit_group syscall entry

[Michael Schmitz <schmitzmic@gmail.com>]

do_exit() calls prace_stop() which may require access to all saved
registers. We only save those registers not preserved by C code
currently.

Provide a special syscall entry for exit and exit_group syscalls
similar to that used by clone and clone3, which have the same
requirements.

No fix to io_uring appears to be needed, because m68k copy_thread
treats kernel threads the same as e.g. alpha does, and copies only
a subset of registers in that case.

CC: Eric W. Biederman <ebiederm@xmission.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
---
 arch/m68k/kernel/entry.S              | 14 ++++++++++++++
 arch/m68k/kernel/process.c            | 16 ++++++++++++++++
 arch/m68k/kernel/syscalls/syscall.tbl |  4 ++--
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 9dd76fb..1e067e6 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -76,6 +76,20 @@ ENTRY(__sys_clone3)
 	lea	%sp@(28),%sp
 	rts
 
+ENTRY(__sys_exit)
+	SAVE_SWITCH_STACK
+	pea	%sp@(SWITCH_STACK_SIZE)
+	jbsr	m68k_exit
+	lea	%sp@(28),%sp
+	rts
+
+ENTRY(__sys_exit_group)
+	SAVE_SWITCH_STACK
+	pea	%sp@(SWITCH_STACK_SIZE)
+	jbsr	m68k_exit_group
+	lea	%sp@(28),%sp
+	rts
+
 ENTRY(sys_sigreturn)
 	SAVE_SWITCH_STACK
 	movel	%sp,%sp@-		  | switch_stack pointer
diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
index da83cc8..df4e5f1 100644
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -138,6 +138,22 @@ asmlinkage int m68k_clone3(struct pt_regs *regs)
 	return sys_clone3((struct clone_args __user *)regs->d1, regs->d2);
 }
 
+/*
+ * Because extra registers are saved on the stack after the sys_exit()
+ * arguments, this C wrapper extracts them from pt_regs * and then calls the
+ * generic sys_exit() implementation.
+ */
+asmlinkage int m68k_exit(struct pt_regs *regs)
+{
+	return sys_exit(regs->d1);
+}
+
+/* Same for sys_exit_group ... */
+asmlinkage int m68k_exit_group(struct pt_regs *regs)
+{
+	return sys_exit_group(regs->d1);
+}
+
 int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
 		struct task_struct *p, unsigned long tls)
 {
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 0dd019d..3d5b6fbc 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -8,7 +8,7 @@
 # The <abi> is always "common" for this file
 #
 0	common	restart_syscall			sys_restart_syscall
-1	common	exit				sys_exit
+1	common	exit				__sys_exit
 2	common	fork				__sys_fork
 3	common	read				sys_read
 4	common	write				sys_write
@@ -254,7 +254,7 @@
 244	common	io_submit			sys_io_submit
 245	common	io_cancel			sys_io_cancel
 246	common	fadvise64			sys_fadvise64
-247	common	exit_group			sys_exit_group
+247	common	exit_group			__sys_exit_group
 248	common	lookup_dcookie			sys_lookup_dcookie
 249	common	epoll_create			sys_epoll_create
 250	common	epoll_ctl			sys_epoll_ctl
-- 
2.7.4