powerpc: Make syscall tracing use tracehook.h helpers

This changes powerpc syscall tracing to use the new tracehook.h entry
points.  There is no change, only cleanup.

In addition, the assembly changes allow do_syscall_trace_enter() to
abort the syscall without losing the information about the original
r0 value.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/entry_32.S

@@ -343,7 +343,12 @@ syscall_dotrace:
 	stw	r0,_TRAP(r1)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_syscall_trace_enter
-	lwz	r0,GPR0(r1)	/* Restore original registers */
+	/*
+	 * Restore argument registers possibly just changed.
+	 * We use the return value of do_syscall_trace_enter
+	 * for call number to look up in the table (r0).
+	 */
+	mr	r0,r3
 	lwz	r3,GPR3(r1)
 	lwz	r4,GPR4(r1)
 	lwz	r5,GPR5(r1)

arch/powerpc/kernel/entry_64.S

@@ -214,7 +214,12 @@ syscall_dotrace:
 	bl	.save_nvgprs
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	.do_syscall_trace_enter
-	ld	r0,GPR0(r1)	/* Restore original registers */
+	/*
+	 * Restore argument registers possibly just changed.
+	 * We use the return value of do_syscall_trace_enter
+	 * for the call number to look up in the table (r0).
+	 */
+	mr	r0,r3
 	ld	r3,GPR3(r1)
 	ld	r4,GPR4(r1)
 	ld	r5,GPR5(r1)

arch/powerpc/kernel/ptrace.c

@@ -22,6 +22,7 @@
 #include <linux/errno.h>
 #include <linux/ptrace.h>
 #include <linux/regset.h>
+#include <linux/tracehook.h>
 #include <linux/elf.h>
 #include <linux/user.h>
 #include <linux/security.h>
@@ -1014,31 +1015,24 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 	return ret;
 }
 
-static void do_syscall_trace(void)
+/*
+ * We must return the syscall number to actually look up in the table.
+ * This can be -1L to skip running any syscall at all.
+ */
+long do_syscall_trace_enter(struct pt_regs *regs)
 {
-	/* 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)
-				 ? 0x80 : 0));
-
-	/*
-	 * this isn't the same as continuing with a signal, but it will do
-	 * for normal use.  strace only continues with a signal if the
-	 * stopping signal is not SIGTRAP.  -brl
-	 */
-	if (current->exit_code) {
-		send_sig(current->exit_code, current, 1);
-		current->exit_code = 0;
-	}
-}
+	long ret = 0;
 
-void do_syscall_trace_enter(struct pt_regs *regs)
-{
 	secure_computing(regs->gpr[0]);
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE)
-	    && (current->ptrace & PT_PTRACED))
-		do_syscall_trace();
+	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
+	    tracehook_report_syscall_entry(regs))
+		/*
+		 * Tracing decided this syscall should not happen.
+		 * We'll return a bogus call number to get an ENOSYS
+		 * error, but leave the original number in regs->gpr[0].
+		 */
+		ret = -1L;
 
 	if (unlikely(current->audit_context)) {
 #ifdef CONFIG_PPC64
@@ -1056,16 +1050,19 @@ void do_syscall_trace_enter(struct pt_regs *regs)
 					    regs->gpr[5] & 0xffffffff,
 					    regs->gpr[6] & 0xffffffff);
 	}
+
+	return ret ?: regs->gpr[0];
 }
 
 void do_syscall_trace_leave(struct pt_regs *regs)
 {
+	int step;
+
 	if (unlikely(current->audit_context))
 		audit_syscall_exit((regs->ccr&0x10000000)?AUDITSC_FAILURE:AUDITSC_SUCCESS,
 				   regs->result);
 
-	if ((test_thread_flag(TIF_SYSCALL_TRACE)
-	     || test_thread_flag(TIF_SINGLESTEP))
-	    && (current->ptrace & PT_PTRACED))
-		do_syscall_trace();
+	step = test_thread_flag(TIF_SINGLESTEP);
+	if (step || test_thread_flag(TIF_SYSCALL_TRACE))
+		tracehook_report_syscall_exit(regs, step);
 }