[PATCH v2 1/3] powerpc: Don't force ENOSYS as error on syscall fail

[Bogdan Purcareata <bogdan.purcareata@freescale.com>]

In certain scenarios - e.g. seccomp filtering with ERRNO as default action -
the system call fails for other reasons than the syscall not being available.
The seccomp filter can be configured to store a user-defined error code on
return from a blacklisted syscall. Don't always set ENOSYS on
do_syscall_trace_enter failure.

v2:
- move setting ENOSYS as errno from the syscall entry assembly to
  do_syscall_trace_enter, only in the specific case

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@freescale.com>
---
 arch/powerpc/kernel/entry_32.S | 2 +-
 arch/powerpc/kernel/entry_64.S | 1 -
 arch/powerpc/kernel/ptrace.c   | 4 +++-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 10a0935..d2c58a3 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -425,7 +425,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
 	b	1b
 #endif  /* CONFIG_44x */
 
-66:	li	r3,-ENOSYS
+66:
 	b	ret_from_syscall
 
 	.globl	ret_from_fork
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 194e46d..0111e04 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -269,7 +269,6 @@ syscall_dotrace:
 	b	.Lsyscall_dotrace_cont
 
 syscall_enosys:
-	li	r3,-ENOSYS
 	b	syscall_exit
 	
 syscall_exit_work:
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index f21897b..d82fd0b 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1775,13 +1775,15 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 	secure_computing_strict(regs->gpr[0]);
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
-	    tracehook_report_syscall_entry(regs))
+	    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;
+		syscall_set_return_value(current, regs, -ENOSYS, 0);
+	}
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->gpr[0]);
-- 
2.1.4