selftests: vDSO: vdso_standalone_test_x86: Switch to nolibc

vdso_standalone_test_x86 provides its own ASM syscall wrappers and
_start() implementation. The in-tree nolibc library already provides
this functionality for multiple architectures. By making use of nolibc,
the standalone testcase can be built from the exact same codebase as the
non-standalone version.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/all/20250226-parse_vdso-nolibc-v2-16-28e14e031ed8@linutronix.de

Author: t-8ch

tools/testing/selftests/vDSO/Makefile

@@ -22,13 +22,17 @@ include ../lib.mk
 
 CFLAGS += $(TOOLS_INCLUDES)
 
+CFLAGS_NOLIBC := -nostdlib -nostdinc -ffreestanding -fno-asynchronous-unwind-tables \
+		 -fno-stack-protector -include $(top_srcdir)/tools/include/nolibc/nolibc.h \
+		 -I$(top_srcdir)/tools/include/nolibc/ $(KHDR_INCLUDES)
+
 $(OUTPUT)/vdso_test_gettimeofday: parse_vdso.c vdso_test_gettimeofday.c
 $(OUTPUT)/vdso_test_getcpu: parse_vdso.c vdso_test_getcpu.c
 $(OUTPUT)/vdso_test_abi: parse_vdso.c vdso_test_abi.c
 $(OUTPUT)/vdso_test_clock_getres: vdso_test_clock_getres.c
 
-$(OUTPUT)/vdso_standalone_test_x86: vdso_standalone_test_x86.c parse_vdso.c
-$(OUTPUT)/vdso_standalone_test_x86: CFLAGS +=-nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector
+$(OUTPUT)/vdso_standalone_test_x86: vdso_standalone_test_x86.c parse_vdso.c | headers
+$(OUTPUT)/vdso_standalone_test_x86: CFLAGS:=$(CFLAGS_NOLIBC) $(CFLAGS)
 
 $(OUTPUT)/vdso_test_correctness: vdso_test_correctness.c
 $(OUTPUT)/vdso_test_correctness: LDFLAGS += -ldl

tools/testing/selftests/vDSO/vdso_standalone_test_x86.c

@@ -1,167 +1,58 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * vdso_test.c: Sample code to test parse_vdso.c on x86
- * Copyright (c) 2011-2014 Andy Lutomirski
+ * vdso_test_gettimeofday.c: Sample code to test parse_vdso.c and
+ *                           vDSO gettimeofday()
+ * Copyright (c) 2014 Andy Lutomirski
  *
- * You can amuse yourself by compiling with:
- * gcc -std=gnu99 -nostdlib
- *     -Os -fno-asynchronous-unwind-tables -flto -lgcc_s
- *      vdso_standalone_test_x86.c parse_vdso.c
- * to generate a small binary.  On x86_64, you can omit -lgcc_s
- * if you want the binary to be completely standalone.
+ * Compile with:
+ * gcc -std=gnu99 vdso_test_gettimeofday.c parse_vdso_gettimeofday.c
+ *
+ * Tested on x86, 32-bit and 64-bit.  It may work on other architectures, too.
  */
 
-#include <sys/syscall.h>
+#include <stdio.h>
+#ifndef NOLIBC
+#include <sys/auxv.h>
 #include <sys/time.h>
-#include <unistd.h>
-#include <stdint.h>
-#include <linux/auxvec.h>
-
-#include "parse_vdso.h"
-
-/* We need some libc functions... */
-int strcmp(const char *a, const char *b)
-{
-	/* This implementation is buggy: it never returns -1. */
-	while (*a || *b) {
-		if (*a != *b)
-			return 1;
-		if (*a == 0 || *b == 0)
-			return 1;
-		a++;
-		b++;
-	}
-
-	return 0;
-}
-
-/*
- * The clang build needs this, although gcc does not.
- * Stolen from lib/string.c.
- */
-void *memcpy(void *dest, const void *src, size_t count)
-{
-	char *tmp = dest;
-	const char *s = src;
-
-	while (count--)
-		*tmp++ = *s++;
-	return dest;
-}
-
-/* ...and two syscalls.  This is x86-specific. */
-static inline long x86_syscall3(long nr, long a0, long a1, long a2)
-{
-	long ret;
-#ifdef __x86_64__
-	asm volatile ("syscall" : "=a" (ret) : "a" (nr),
-		      "D" (a0), "S" (a1), "d" (a2) :
-		      "cc", "memory", "rcx",
-		      "r8", "r9", "r10", "r11" );
-#else
-	asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
-		      "b" (a0), "c" (a1), "d" (a2) :
-		      "cc", "memory" );
 #endif
-	return ret;
-}
-
-static inline long linux_write(int fd, const void *data, size_t len)
-{
-	return x86_syscall3(__NR_write, fd, (long)data, (long)len);
-}
 
-static inline void linux_exit(int code)
-{
-	x86_syscall3(__NR_exit, code, 0, 0);
-}
-
-void to_base10(char *lastdig, time_t n)
-{
-	while (n) {
-		*lastdig = (n % 10) + '0';
-		n /= 10;
-		lastdig--;
-	}
-}
+#include "../kselftest.h"
+#include "parse_vdso.h"
+#include "vdso_config.h"
+#include "vdso_call.h"
 
-unsigned long getauxval(const unsigned long *auxv, unsigned long type)
+int main(int argc, char **argv)
 {
-	unsigned long ret;
-
-	if (!auxv)
-		return 0;
-
-	while (1) {
-		if (!auxv[0] && !auxv[1]) {
-			ret = 0;
-			break;
-		}
+	const char *version = versions[VDSO_VERSION];
+	const char **name = (const char **)&names[VDSO_NAMES];
 
-		if (auxv[0] == type) {
-			ret = auxv[1];
-			break;
-		}
-
-		auxv += 2;
+	unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
+	if (!sysinfo_ehdr) {
+		printf("AT_SYSINFO_EHDR is not present!\n");
+		return KSFT_SKIP;
 	}
 
-	return ret;
-}
-
-void c_main(void **stack)
-{
-	/* Parse the stack */
-	long argc = (long)*stack;
-	stack += argc + 2;
-
-	/* Now we're pointing at the environment.  Skip it. */
-	while(*stack)
-		stack++;
-	stack++;
-
-	/* Now we're pointing at auxv.  Initialize the vDSO parser. */
-	vdso_init_from_sysinfo_ehdr(getauxval((unsigned long *)stack, AT_SYSINFO_EHDR));
+	vdso_init_from_sysinfo_ehdr(getauxval(AT_SYSINFO_EHDR));
 
 	/* Find gettimeofday. */
 	typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
-	gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
+	gtod_t gtod = (gtod_t)vdso_sym(version, name[0]);
 
-	if (!gtod)
-		linux_exit(1);
+	if (!gtod) {
+		printf("Could not find %s\n", name[0]);
+		return KSFT_SKIP;
+	}
 
 	struct timeval tv;
-	long ret = gtod(&tv, 0);
+	long ret = VDSO_CALL(gtod, 2, &tv, 0);
 
 	if (ret == 0) {
-		char buf[] = "The time is                     .000000\n";
-		to_base10(buf + 31, tv.tv_sec);
-		to_base10(buf + 38, tv.tv_usec);
-		linux_write(1, buf, sizeof(buf) - 1);
+		printf("The time is %lld.%06lld\n",
+		       (long long)tv.tv_sec, (long long)tv.tv_usec);
 	} else {
-		linux_exit(ret);
+		printf("%s failed\n", name[0]);
+		return KSFT_FAIL;
 	}
 
-	linux_exit(0);
+	return 0;
 }
-
-/*
- * This is the real entry point.  It passes the initial stack into
- * the C entry point.
- */
-asm (
-	".text\n"
-	".global _start\n"
-	".type _start,@function\n"
-	"_start:\n\t"
-#ifdef __x86_64__
-	"mov %rsp,%rdi\n\t"
-	"and $-16,%rsp\n\t"
-	"sub $8,%rsp\n\t"
-	"jmp c_main"
-#else
-	"push %esp\n\t"
-	"call c_main\n\t"
-	"int $3"
-#endif
-	);