selftests/fpu: Add an FPU selftest

	  If unsure, say N.

config TEST_FPU

	tristate "Test floating point operations in kernel space"

	depends on X86 && !KCOV_INSTRUMENT_ALL

	help

	  Enable this option to add /sys/kernel/debug/selftest_helpers/test_fpu

	  which will trigger a sequence of floating point operations. This is used

	  for self-testing floating point control register setting in

	  kernel_fpu_begin().

	  If unsure, say N.

endif # RUNTIME_TESTING_MENU

config MEMTEST

obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o

obj-$(CONFIG_TEST_HMM) += test_hmm.o

#

# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns

# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS

# get appended last to CFLAGS and thus override those previous compiler options.

#

FPU_CFLAGS := -mhard-float -msse -msse2

ifdef CONFIG_CC_IS_GCC

# Stack alignment mismatch, proceed with caution.

# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3

# (8B stack alignment).

# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383

#

# The "-msse" in the first argument is there so that the

# -mpreferred-stack-boundary=3 build error:

#

#  -mpreferred-stack-boundary=3 is not between 4 and 12

#

# can be triggered. Otherwise gcc doesn't complain.

FPU_CFLAGS += $(call cc-option,-msse -mpreferred-stack-boundary=3,-mpreferred-stack-boundary=4)

endif

obj-$(CONFIG_TEST_FPU) += test_fpu.o

CFLAGS_test_fpu.o += $(FPU_CFLAGS)

obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/

obj-$(CONFIG_KUNIT) += kunit/

// SPDX-License-Identifier: GPL-2.0+

/*

 * Test cases for using floating point operations inside a kernel module.

 *

 * This tests kernel_fpu_begin() and kernel_fpu_end() functions, especially

 * when userland has modified the floating point control registers. The kernel

 * state might depend on the state set by the userland thread that was active

 * before a syscall.

 *

 * To facilitate the test, this module registers file

 * /sys/kernel/debug/selftest_helpers/test_fpu, which when read causes a

 * sequence of floating point operations. If the operations fail, either the

 * read returns error status or the kernel crashes.

 * If the operations succeed, the read returns "1\n".

 */

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/debugfs.h>

#include <asm/fpu/api.h>

static int test_fpu(void)

{

	/*

	 * This sequence of operations tests that rounding mode is

	 * to nearest and that denormal numbers are supported.

	 * Volatile variables are used to avoid compiler optimizing

	 * the calculations away.

	 */

	volatile double a, b, c, d, e, f, g;

	a = 4.0;

	b = 1e-15;

	c = 1e-310;

	/* Sets precision flag */

	d = a + b;

	/* Result depends on rounding mode */

	e = a + b / 2;

	/* Denormal and very large values */

	f = b / c;

	/* Depends on denormal support */

	g = a + c * f;

	if (d > a && e > a && g > a)

		return 0;

	else

		return -EINVAL;

}

static int test_fpu_get(void *data, u64 *val)

{

	int status = -EINVAL;

	kernel_fpu_begin();

	status = test_fpu();

	kernel_fpu_end();

	*val = 1;

	return status;

}

DEFINE_SIMPLE_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");

static struct dentry *selftest_dir;

static int __init test_fpu_init(void)

{

	selftest_dir = debugfs_create_dir("selftest_helpers", NULL);

	if (!selftest_dir)

		return -ENOMEM;

	debugfs_create_file("test_fpu", 0444, selftest_dir, NULL,

			    &test_fpu_fops);

	return 0;

}

static void __exit test_fpu_exit(void)

{

	debugfs_remove(selftest_dir);

}

module_init(test_fpu_init);

module_exit(test_fpu_exit);

MODULE_LICENSE("GPL");

TARGETS += filesystems/binderfs

TARGETS += filesystems/epoll

TARGETS += firmware

TARGETS += fpu

TARGETS += ftrace

TARGETS += futex

TARGETS += gpio

# SPDX-License-Identifier: GPL-2.0+

test_fpu