ARM: 7456/1: ptrace: provide separate functions for tracing syscall {entry,exit}

The syscall_trace on ARM takes a `why' parameter to indicate whether or
not we are entering or exiting a system call. This can be confusing for
people looking at the code since (a) it conflicts with the why register
alias in the entry assembly code and (b) it is not immediately clear
what it represents.

This patch splits up the syscall_trace function into separate wrappers
for syscall entry and exit, allowing the low-level syscall handling
code to branch to the appropriate function.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 31 insertions, 20 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 10911c93fbf1..49d9f9305247 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -442,10 +442,9 @@ ENDPROC(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
+        mov     r1, scno
+        add     r0, sp, #S_OFF
+        bl      syscall_trace_enter
 
         adr     lr, BSYM(__sys_trace_return)    @ return address
         mov     scno, r0                        @ syscall number (possibly new)
@@ -457,10 +456,9 @@ __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
+        mov     r1, scno
+        mov     r0, sp
+        bl      syscall_trace_exit
         b       ret_slow_syscall
 
         .align  5
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 592a39d0ef31..dab711e6e1ca 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -907,12 +907,18 @@ long arch_ptrace(struct task_struct *child, long request,
         return ret;
 }
 
-asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
+enum ptrace_syscall_dir {
+        PTRACE_SYSCALL_ENTER = 0,
+        PTRACE_SYSCALL_EXIT,
+};
+
+static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
+                                enum ptrace_syscall_dir dir)
 {
         unsigned long ip;
 
         if (!test_thread_flag(TIF_SYSCALL_TRACE))
-                goto out_no_trace;
+                return scno;
 
         current_thread_info()->syscall = scno;
 
@@ -921,21 +927,28 @@ asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
          * IP = 0 -> entry, =1 -> exit
          */
         ip = regs->ARM_ip;
-        regs->ARM_ip = why;
+        regs->ARM_ip = dir;
 
-        if (why)
+        if (dir == PTRACE_SYSCALL_EXIT)
                 tracehook_report_syscall_exit(regs, 0);
         else if (tracehook_report_syscall_entry(regs))
                 current_thread_info()->syscall = -1;
 
         regs->ARM_ip = ip;
-        scno = current_thread_info()->syscall;
+        return current_thread_info()->syscall;
+}
 
-out_no_trace:
-        if (why)
-                audit_syscall_exit(regs);
-        else
-                audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0,
-                                    regs->ARM_r1, regs->ARM_r2, regs->ARM_r3);
-        return scno;
+asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
+{
+        int ret = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_ENTER);
+        audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,
+                            regs->ARM_r2, regs->ARM_r3);
+        return ret;
+}
+
+asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
+{
+        int ret = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_EXIT);
+        audit_syscall_exit(regs);
+        return ret;
 }