[PATCH v13 1/3] m68k/kernel - check syscall_trace_enter() return code on m68k

[Michael Schmitz <schmitzmic@gmail.com>]

Check return code of syscall_trace_enter(), and skip syscall
if -1. Return code will be left at what had been set by
ptrace or seccomp (in regs->d0).

No regression seen in testing with strace on ARAnyM.

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>

--
Changes from v12:

- prevent overwriting the syscall return value after change
  by ptrace or seccomp on 68020+

Changes from v7:

Al Viro:
- split return code checks from switch to syscall_trace_enter()

Changes from v6:

Geert Uytterhoeven:
- add syscall_trace_enter() return code check for 68000
  and coldfire

Changes from v5:

- add comment to explain optimization

Changes from v4:

Andreas Schwab:
- optimize return code test (addql #1,%d0 for cmpil #-1,%d0)
- spelling fix in commit message

Changes from v3:

- change syscall_trace_enter return code test from !=0 to ==-1
---
 arch/m68k/68000/entry.S    | 2 ++
 arch/m68k/coldfire/entry.S | 2 ++
 arch/m68k/kernel/entry.S   | 3 +++
 3 files changed, 7 insertions(+)

diff --git a/arch/m68k/68000/entry.S b/arch/m68k/68000/entry.S
index 997b54933015..7d63e2f1555a 100644
--- a/arch/m68k/68000/entry.S
+++ b/arch/m68k/68000/entry.S
@@ -45,6 +45,8 @@ do_trace:
 	jbsr	syscall_trace_enter
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
+	addql	#1,%d0
+	jeq	ret_from_exception
 	movel	%sp@(PT_OFF_ORIG_D0),%d1
 	movel	#-ENOSYS,%d0
 	cmpl	#NR_syscalls,%d1
diff --git a/arch/m68k/coldfire/entry.S b/arch/m68k/coldfire/entry.S
index 9f337c70243a..35104c5417ff 100644
--- a/arch/m68k/coldfire/entry.S
+++ b/arch/m68k/coldfire/entry.S
@@ -90,6 +90,8 @@ ENTRY(system_call)
 	jbsr	syscall_trace_enter
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
+	addql	#1,%d0
+	jeq	ret_from_exception
 	movel	%d3,%a0
 	jbsr	%a0@
 	movel	%d0,%sp@(PT_OFF_D0)		/* save the return value */
diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 18f278bdbd21..42879e6eb651 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -184,9 +184,12 @@ do_trace_entry:
 	jbsr	syscall_trace_enter
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
+	addql	#1,%d0			| optimization for cmpil #-1,%d0
+	jeq	ret_from_syscall
 	movel	%sp@(PT_OFF_ORIG_D0),%d0
 	cmpl	#NR_syscalls,%d0
 	jcs	syscall
+	jra	ret_from_syscall
 badsys:
 	movel	#-ENOSYS,%sp@(PT_OFF_D0)
 	jra	ret_from_syscall
-- 
2.17.1