syscall.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/syscall.c b/syscall.c
index e66ac0a95582..edd9cb804318 100644
--- a/syscall.c
+++ b/syscall.c
@@ -901,14 +901,31 @@ get_scno(struct tcb *tcp)
 		long val;
 		int pid = tcp->pid;
 
+		/* Check the high bits of eflags for processor mode */
+		if (upeek(tcp, 8*EFLAGS, &val) < 0)
+			return -1;
+		val >>= 32;
 		/* Check CS register value. On x86-64 linux it is:
 		 * 	0x33	for long mode (64 bit)
 		 * 	0x23	for compatibility mode (32 bit)
 		 * It takes only one ptrace and thus doesn't need
 		 * to be cached.
 		 */
-		if (upeek(tcp, 8*CS, &val) < 0)
-			return -1;
+		switch (val & 3) {
+		case 0:
+			/* Legacu case: check CS */
+			if (upeek(tcp, 8*CS, &val) < 0)
+				return -1;
+			break;
+		case 1:
+			/* "Long mode" value */
+			val = 0x33;
+			break;
+		case 2:
+			/* Compatibility mode */
+			val = 0x23;
+			break;
+		}
 		switch (val) {
 			case 0x23: currpers = 1; break;
 			case 0x33: currpers = 0; break;