[RFC,11/12] selftests/fpu: Move FP code to a separate translation unit

Commit Message

Samuel Holland Dec. 8, 2023, 5:54 a.m. UTC

This ensures no compiler-generated floating-point code can appear
outside kernel_fpu_{begin,end}() sections, and some architectures
enforce this separation.

Signed-off-by: Samuel Holland <[e-mail]>
---

 lib/Makefile                        |  3 ++-
 lib/{test_fpu.c => test_fpu_glue.c} | 32 +-------------------------
 lib/test_fpu_impl.c                 | 35 +++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 32 deletions(-)
 rename lib/{test_fpu.c => test_fpu_glue.c} (71%)
 create mode 100644 lib/test_fpu_impl.c

Comments

Christoph Hellwig Dec. 11, 2023, 4:18 p.m. UTC | #1

>  obj-$(CONFIG_TEST_FPU) += test_fpu.o
> -CFLAGS_test_fpu.o += $(FPU_CFLAGS)
> +test_fpu-y := test_fpu_glue.o test_fpu_impl.o
> +CFLAGS_test_fpu_impl.o += $(FPU_CFLAGS)

Btw, I really wonder if having a

modname-fpu += foo.o

syntax in kbuild wouldn't be preferable to this.  Of coure that requires
someone who understands kbuild inside out.

> +int test_fpu(void);

This needs to go into a header.

And I think I underatand your way to enforce the use of a separate
compilation unit in the riscv patch now.

Can we just make that generic, e.g. have a <linux/fpu.h> that wraps
<asm/fpu.h> that does the guard based on a
-D_LINUX_FPU_COMPILATION_UNIT=1 on the command line so that all the
code becomes fully portable?  Any legacy arch specific fpu users not
using <linux/fpu.h> would not be affected by it, although it would be
great to eventually migrate them to the common scheme.

Patch

diff --git a/lib/Makefile b/lib/Makefile
index 6b09731d8e61..e7cbd54944a2 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -132,7 +132,8 @@  FPU_CFLAGS += $(call cc-option,-msse -mpreferred-stack-boundary=3,-mpreferred-st
 endif
 
 obj-$(CONFIG_TEST_FPU) += test_fpu.o
-CFLAGS_test_fpu.o += $(FPU_CFLAGS)
+test_fpu-y := test_fpu_glue.o test_fpu_impl.o
+CFLAGS_test_fpu_impl.o += $(FPU_CFLAGS)
 
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
diff --git a/lib/test_fpu.c b/lib/test_fpu_glue.c
similarity index 71%
rename from lib/test_fpu.c
rename to lib/test_fpu_glue.c
index e82db19fed84..2761b51117b0 100644
--- a/lib/test_fpu.c
+++ b/lib/test_fpu_glue.c
@@ -19,37 +19,7 @@ 
 #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;
-}
+int test_fpu(void);
 
 static int test_fpu_get(void *data, u64 *val)
 {
diff --git a/lib/test_fpu_impl.c b/lib/test_fpu_impl.c
new file mode 100644
index 000000000000..2ff01980bc22
--- /dev/null
+++ b/lib/test_fpu_impl.c
@@ -0,0 +1,35 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/errno.h>
+
+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;
+}