[PATCH 3/3] selftests/x86: Add syscall_nt selftest

[Andy Lutomirski <luto@kernel.org>]

I've had this sitting around for a while.  Add it to the selftests
tree.  Far Cry running under Wine depends on this behavior.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 tools/testing/selftests/x86/Makefile     |  2 +-
 tools/testing/selftests/x86/syscall_nt.c | 54 ++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/x86/syscall_nt.c

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 1cda40be06ca..2221f2ba449d 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -4,7 +4,7 @@ include ../lib.mk
 
 .PHONY: all all_32 all_64 warn_32bit_failure clean
 
-TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs
+TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt
 TARGETS_C_32BIT_ONLY := entry_from_vm86 sigreturn
 
 TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
diff --git a/tools/testing/selftests/x86/syscall_nt.c b/tools/testing/selftests/x86/syscall_nt.c
new file mode 100644
index 000000000000..60c06af4646a
--- /dev/null
+++ b/tools/testing/selftests/x86/syscall_nt.c
@@ -0,0 +1,54 @@
+/*
+ * syscall_nt.c - checks syscalls with NT set
+ * Copyright (c) 2014-2015 Andrew Lutomirski
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * Some obscure user-space code requires the ability to make system calls
+ * with FLAGS.NT set.  Make sure it works.
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <asm/processor-flags.h>
+
+#ifdef __x86_64__
+# define WIDTH "q"
+#else
+# define WIDTH "l"
+#endif
+
+static unsigned long get_eflags(void)
+{
+	unsigned long eflags;
+	asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
+	return eflags;
+}
+
+static void set_eflags(unsigned long eflags)
+{
+	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
+		      : : "rm" (eflags) : "flags");
+}
+
+int main()
+{
+	printf("[RUN]\tSet NT and issue a syscall\n");
+	set_eflags(get_eflags() | X86_EFLAGS_NT);
+	syscall(SYS_getpid);
+	if (get_eflags() & X86_EFLAGS_NT) {
+		printf("[OK]\tThe syscall worked and NT is still set\n");
+		return 0;
+	} else {
+		printf("[FAIL]\tThe syscall worked but NT was cleared\n");
+		return 1;
+	}
+}
-- 
2.4.3