[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>

2 files changed, 15 insertions, 3 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
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index e591f72bcdeb..7b6256bb590e 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -766,6 +766,11 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
                                        (unsigned long __user *) data);
                         break;
 
+                case PTRACE_SET_SYSCALL:
+                        ret = 0;
+                        child->ptrace_message = data;
+                        break;
+
                 default:
                         ret = ptrace_request(child, request, addr, data);
                         break;
@@ -774,14 +779,14 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
         return ret;
 }
 
-asmlinkage void syscall_trace(int why, struct pt_regs *regs)
+asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
 {
         unsigned long ip;
 
         if (!test_thread_flag(TIF_SYSCALL_TRACE))
-                return;
+                return scno;
         if (!(current->ptrace & PT_PTRACED))
-                return;
+                return scno;
 
         /*
          * Save IP.  IP is used to denote syscall entry/exit:
@@ -790,6 +795,8 @@ asmlinkage void syscall_trace(int why, struct pt_regs *regs)
         ip = regs->ARM_ip;
         regs->ARM_ip = why;
 
+        current->ptrace_message = scno;
+
         /* the 0x80 provides a way for the tracing parent to distinguish
            between a syscall stop and SIGTRAP delivery */
         ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
@@ -804,4 +811,6 @@ asmlinkage void syscall_trace(int why, struct pt_regs *regs)
                 current->exit_code = 0;
         }
         regs->ARM_ip = ip;
+
+        return current->ptrace_message;
 }