From 2c10d8ca605c8ebd24fbb2e920a91bd5ae04ec36 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Wed, 18 Mar 2015 16:44:25 -0700
Subject: segregs: Use int 0x80 syscalls to avoid sysexit issues

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 segregs.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/segregs.c b/segregs.c
index d6fdff1..a0c34b8 100644
--- a/segregs.c
+++ b/segregs.c
@@ -1,14 +1,14 @@
+/*
+ * Copyright (c) 2014-2015 Andy Lutomirski
+ * GPL v2
+ */
+
 #include <stdio.h>
-#include <stdbool.h>
-#include <sys/syscall.h>
 #include <unistd.h>
-#include <asm/ldt.h>
+#include <time.h>
 #include <err.h>
-#include <sys/user.h>
-
-#ifdef __x86_64__
-# error This test is 32-bit only
-#endif
+#include <asm/ldt.h>
+#include <sys/syscall.h>
 
 static unsigned short GDT3(int idx)
 {
@@ -46,8 +46,22 @@ int main()
 	int errors = 0;
 	int total = 1000;
 	for (int i = 0; i < total; i++) {
+		struct timespec req = {
+			.tv_sec = 0,
+			.tv_nsec = 100000,
+		};
+		int ret;
+
 		asm volatile ("mov %0,%%es" : : "rm" (GDT3(idx)));
-		usleep(100);
+
+		/*
+		 * Force rescheduling.  On 32-bit kernels, fast syscalls
+		 * destroy DS and ES, so force int 80.
+		 */
+		asm volatile ("int $0x80"
+			      : "=a" (ret)
+			      : "a" (SYS_nanosleep), "b" (&req),
+				"c" (0));
 
 		unsigned short es;
 		asm volatile ("mov %%es,%0" : "=rm" (es));
-- 
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