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- // 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_DEBUGFS_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_unsafe("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");
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