Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs

This fix two related bugs:
* PTRACE_GETREGS doesn't get the right orig_ax (syscall) value
* PTRACE_SETREGS can't set the orig_ax value (erased by initial value)

Remove the now useless and error-prone get_syscall().

Signed-off-by: Mickaël Salaün <redacted>
Cc: Jeff Dike <redacted>
Cc: Richard Weinberger <richard-/L3Ra7n9ekc@public.gmane.org>
Cc: Thomas Gleixner <redacted>
Cc: Kees Cook <redacted>
Cc: Andy Lutomirski <redacted>
Cc: Will Drewry <redacted>
Cc: Thomas Meyer <redacted>
Cc: Nicolas Iooss <redacted>
Cc: Anton Ivanov <redacted>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: user-mode-linux-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Cc: user-mode-linux-user-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Cc: Meredydd Luff <redacted>
Cc: David Drysdale <redacted>
---
 arch/um/kernel/skas/syscall.c   | 7 ++++++-
 arch/um/os-Linux/skas/process.c | 7 -------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index 1683b8e..65f0d1a 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c

@@ -7,6 +7,7 @@
 #include <linux/ptrace.h>
 #include <kern_util.h>
 #include <sysdep/ptrace.h>
+#include <sysdep/ptrace_user.h>
 #include <sysdep/syscalls.h>
 #include <os.h>
 

@@ -16,12 +17,16 @@ void handle_syscall(struct uml_pt_regs *r)
 	long result;
 	int syscall;
 
+	/* Save the syscall register. */
+	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
+
 	if (syscall_trace_enter(regs)) {
 		result = -ENOSYS;
 		goto out;
 	}
 
-	syscall = get_syscall(r);
+	/* Get the syscall after being potentially updated with ptrace. */
+	syscall = UPT_SYSCALL_NR(r);