selftests/x86: Consolidate and fix get/set_eflags() helpers

There are several copies of get_eflags() and set_eflags() and they all are
buggy. Consolidate them and fix them. The fixes are:

Add memory clobbers. These are probably unnecessary but they make sure
that the compiler doesn't move something past one of these calls when it
shouldn't.

Respect the redzone on x86_64. There has no failure been observed related
to this, but it's definitely a bug.

Signed-off-by: Andy Lutomirski <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

tools/testing/selftests/x86/Makefile

···
 
 EXTRA_CLEAN := $(BINARIES_32) $(BINARIES_64)
 
-$(BINARIES_32): $(OUTPUT)/%_32: %.c
+$(BINARIES_32): $(OUTPUT)/%_32: %.c helpers.h
 	$(CC) -m32 -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl -lm
 
-$(BINARIES_64): $(OUTPUT)/%_64: %.c
+$(BINARIES_64): $(OUTPUT)/%_64: %.c helpers.h
 	$(CC) -m64 -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl
 
 # x86_64 users should be encouraged to install 32-bit libraries

tools/testing/selftests/x86/helpers.h

···
+// SPDX-License-Identifier: GPL-2.0-only
+#ifndef __SELFTESTS_X86_HELPERS_H
+#define __SELFTESTS_X86_HELPERS_H
+
+#include <asm/processor-flags.h>
+
+static inline unsigned long get_eflags(void)
+{
+	unsigned long eflags;
+
+	asm volatile (
+#ifdef __x86_64__
+		"subq $128, %%rsp\n\t"
+		"pushfq\n\t"
+		"popq %0\n\t"
+		"addq $128, %%rsp"
+#else
+		"pushfl\n\t"
+		"popl %0"
+#endif
+		: "=r" (eflags) :: "memory");
+
+	return eflags;
+}
+
+static inline void set_eflags(unsigned long eflags)
+{
+	asm volatile (
+#ifdef __x86_64__
+		"subq $128, %%rsp\n\t"
+		"pushq %0\n\t"
+		"popfq\n\t"
+		"addq $128, %%rsp"
+#else
+		"pushl %0\n\t"
+		"popfl"
+#endif
+		:: "r" (eflags) : "flags", "memory");
+}
+
+#endif /* __SELFTESTS_X86_HELPERS_H */

tools/testing/selftests/x86/single_step_syscall.c

···
 #include <sys/ptrace.h>
 #include <sys/user.h>
 
+#include "helpers.h"
+
 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 		       int flags)
 {
···
 # define WIDTH "l"
 # define INT80_CLOBBERS
 #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");
-}
-
-#define X86_EFLAGS_TF (1UL << 8)
 
 static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
 {

tools/testing/selftests/x86/syscall_arg_fault.c

···
 #include <setjmp.h>
 #include <errno.h>
 
-#ifdef __x86_64__
-# define WIDTH "q"
-#else
-# define WIDTH "l"
-#endif
+#include "helpers.h"
 
 /* Our sigaltstack scratch space. */
 static unsigned char altstack_data[SIGSTKSZ];
-
-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");
-}
-
-#define X86_EFLAGS_TF (1UL << 8)
 
 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 		       int flags)

tools/testing/selftests/x86/syscall_nt.c

···
 #include <signal.h>
 #include <err.h>
 #include <sys/syscall.h>
-#include <asm/processor-flags.h>
 
-#ifdef __x86_64__
-# define WIDTH "q"
-#else
-# define WIDTH "l"
-#endif
+#include "helpers.h"
 
 static unsigned int nerrs;
-
-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");
-}
 
 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 		       int flags)

tools/testing/selftests/x86/test_vsyscall.c

···
 #include <setjmp.h>
 #include <sys/uio.h>
 
+#include "helpers.h"
+
 #ifdef __x86_64__
 # define VSYS(x) (x)
 #else
···
 }
 
 #ifdef __x86_64__
-#define X86_EFLAGS_TF (1UL << 8)
 static volatile sig_atomic_t num_vsyscall_traps;
-
-static unsigned long get_eflags(void)
-{
-	unsigned long eflags;
-	asm volatile ("pushfq\n\tpopq %0" : "=rm" (eflags));
-	return eflags;
-}
-
-static void set_eflags(unsigned long eflags)
-{
-	asm volatile ("pushq %0\n\tpopfq" : : "rm" (eflags) : "flags");
-}
 
 static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
 {

tools/testing/selftests/x86/unwind_vdso.c

···
 #include <features.h>
 #include <stdio.h>
 
+#include "helpers.h"
+
 #if defined(__GLIBC__) && __GLIBC__ == 2 && __GLIBC_MINOR__ < 16
 
 int main()
···
 	if (sigaction(sig, &sa, 0))
 		err(1, "sigaction");
 }
-
-#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");
-}
-
-#define X86_EFLAGS_TF (1UL << 8)
 
 static volatile sig_atomic_t nerrs;
 static unsigned long sysinfo;