[ARM] 3262/4: allow ptraced syscalls to be overriden

Patch from Nicolas Pitre

This is needed by strace to properly handle the tracing of some system
calls. It could be useful for other applications as well.

Based on an earlier patch from Daniel Jacobowitz.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Daniel Jacobowitz <dan@debian.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 8826d9803aeb..2b92ce85f97f 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -214,11 +214,13 @@ ENTRY(vector_swi)
          * context switches, and waiting for our parent to respond.
          */
 __sys_trace:
+        mov     r2, scno
         add     r1, sp, #S_OFF
         mov     r0, #0                          @ trace entry [IP = 0]
         bl      syscall_trace
 
         adr     lr, __sys_trace_return          @ return address
+        mov     scno, r0                        @ syscall number (possibly new)
         add     r1, sp, #S_R0 + S_OFF           @ pointer to regs
         cmp     scno, #NR_syscalls              @ check upper syscall limit
         ldmccia r1, {r0 - r3}                   @ have to reload r0 - r3
@@ -227,6 +229,7 @@ __sys_trace:
 
 __sys_trace_return:
         str     r0, [sp, #S_R0 + S_OFF]!        @ save returned r0
+        mov     r2, scno
         mov     r1, sp
         mov     r0, #1                          @ trace exit [IP = 1]
         bl      syscall_trace