* [PATCH v5 2/2] lib: make a test module with set/clear bit
2020-02-24 22:50 [PATCH v5 1/2] x86: fix bitops.h warning with a moved cast Jesse Brandeburg
@ 2020-02-24 22:50 ` Jesse Brandeburg
2020-02-25 10:30 ` [PATCH v5 1/2] x86: fix bitops.h warning with a moved cast Andy Shevchenko
1 sibling, 0 replies; 6+ messages in thread
From: Jesse Brandeburg @ 2020-02-24 22:50 UTC (permalink / raw)
To: tglx, mingo, bp
Cc: Jesse Brandeburg, x86, linux-kernel, linux, andriy.shevchenko,
dan.j.williams, peterz
Test some bit clears/sets to make sure assembly doesn't change, and
that the set_bit and clear_bit functions work and don't cause sparse
warnings.
Instruct Kbuild to build this file with extra warning level -Wextra,
to catch new issues, and also doesn't hurt to build with C=1.
This was used to test changes to arch/x86/include/asm/bitops.h.
In particular, sparse (C=1) was very concerned when the last bit
before a natural boundary, like 7, or 31, was being tested, as this
causes sign extension (0xffffff7f) for instance when clearing bit 7.
Recommended usage:
make defconfig
scripts/config -m CONFIG_TEST_BITOPS
make modules_prepare
make C=1 W=1 lib/test_bitops.ko
objdump -S -d lib/test_bitops.ko
insmod lib/test_bitops.ko
rmmod lib/test_bitops.ko
<check dmesg>, there should be no compiler/sparse warnings and no
error messages in log.
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
---
v5: no change
v4: Slight change to bitops_fun last member, as suggested by Andy, added
his reviewed-by too. Added module load/unload to usage. Added copyright.
v3: Update the test to fail if bits aren't cleared, and make the
test reproduce the original issue without patch 1/2, showing that
the issue is fixed in patch 1/2. Thanks PeterZ!
v2: Correct CC: list
---
lib/Kconfig.debug | 13 +++++++
lib/Makefile | 2 +
lib/test_bitops.c | 60 ++++++++++++++++++++++++++++++
tools/testing/selftests/lib/config | 1 +
4 files changed, 76 insertions(+)
create mode 100644 lib/test_bitops.c
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 69def4a9df00..61a5d00ea064 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1947,6 +1947,19 @@ config TEST_LKM
If unsure, say N.
+config TEST_BITOPS
+ tristate "Test module for compilation of clear_bit/set_bit operations"
+ depends on m
+ help
+ This builds the "test_bitops" module that is much like the
+ TEST_LKM module except that it does a basic exercise of the
+ clear_bit and set_bit macros to make sure there are no compiler
+ warnings from C=1 sparse checker or -Wextra compilations. It has
+ no dependencies and doesn't run or load unless explicitly requested
+ by name. for example: modprobe test_bitops.
+
+ If unsure, say N.
+
config TEST_VMALLOC
tristate "Test module for stress/performance analysis of vmalloc allocator"
default n
diff --git a/lib/Makefile b/lib/Makefile
index 611872c06926..b18db565b355 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -89,6 +89,8 @@ obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test_blackhole_dev.o
obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
+obj-$(CONFIG_TEST_BITOPS) += test_bitops.o
+CFLAGS_test_bitops.o += -Werror
obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
diff --git a/lib/test_bitops.c b/lib/test_bitops.c
new file mode 100644
index 000000000000..fd50b3ae4a14
--- /dev/null
+++ b/lib/test_bitops.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Intel Corporation
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+/* a tiny module only meant to test set/clear_bit */
+
+/* use an enum because thats the most common BITMAP usage */
+enum bitops_fun {
+ BITOPS_4 = 4,
+ BITOPS_7 = 7,
+ BITOPS_11 = 11,
+ BITOPS_31 = 31,
+ BITOPS_88 = 88,
+ BITOPS_LAST = 255,
+ BITOPS_LENGTH = 256
+};
+
+static DECLARE_BITMAP(g_bitmap, BITOPS_LENGTH);
+
+static int __init test_bitops_startup(void)
+{
+ pr_warn("Loaded test module\n");
+ set_bit(BITOPS_4, g_bitmap);
+ set_bit(BITOPS_7, g_bitmap);
+ set_bit(BITOPS_11, g_bitmap);
+ set_bit(BITOPS_31, g_bitmap);
+ set_bit(BITOPS_88, g_bitmap);
+ return 0;
+}
+
+static void __exit test_bitops_unstartup(void)
+{
+ int bit_set;
+
+ clear_bit(BITOPS_4, g_bitmap);
+ clear_bit(BITOPS_7, g_bitmap);
+ clear_bit(BITOPS_11, g_bitmap);
+ clear_bit(BITOPS_31, g_bitmap);
+ clear_bit(BITOPS_88, g_bitmap);
+
+ bit_set = find_first_bit(g_bitmap, BITOPS_LAST);
+ if (bit_set != BITOPS_LAST)
+ pr_err("ERROR: FOUND SET BIT %d\n", bit_set);
+
+ pr_warn("Unloaded test module\n");
+}
+
+module_init(test_bitops_startup);
+module_exit(test_bitops_unstartup);
+
+MODULE_AUTHOR("Jesse Brandeburg <jesse.brandeburg@intel.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Bit testing module");
diff --git a/tools/testing/selftests/lib/config b/tools/testing/selftests/lib/config
index 14a77ea4a8da..b80ee3f6e265 100644
--- a/tools/testing/selftests/lib/config
+++ b/tools/testing/selftests/lib/config
@@ -2,3 +2,4 @@ CONFIG_TEST_PRINTF=m
CONFIG_TEST_BITMAP=m
CONFIG_PRIME_NUMBERS=m
CONFIG_TEST_STRSCPY=m
+CONFIG_TEST_BITOPS=m
--
2.24.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v5 1/2] x86: fix bitops.h warning with a moved cast
2020-02-24 22:50 [PATCH v5 1/2] x86: fix bitops.h warning with a moved cast Jesse Brandeburg
2020-02-24 22:50 ` [PATCH v5 2/2] lib: make a test module with set/clear bit Jesse Brandeburg
@ 2020-02-25 10:30 ` Andy Shevchenko
2020-02-25 11:52 ` Andy Shevchenko
2020-02-25 12:50 ` Peter Zijlstra
1 sibling, 2 replies; 6+ messages in thread
From: Andy Shevchenko @ 2020-02-25 10:30 UTC (permalink / raw)
To: Jesse Brandeburg
Cc: tglx, mingo, bp, x86, linux-kernel, linux, dan.j.williams, peterz
On Mon, Feb 24, 2020 at 02:50:19PM -0800, Jesse Brandeburg wrote:
> Fix many sparse warnings when building with C=1.
>
> When the kernel is compiled with C=1, there are lots of messages like:
> arch/x86/include/asm/bitops.h:77:37: warning: cast truncates bits from constant value (ffffff7f becomes 7f)
>
> CONST_MASK() is using a signed integer "1" to create the mask which
> is later cast to (u8) when used, in order to yield an 8-bit value
> for the assembly instructions to use. Simplify the expressions used to
> clearly indicate they are working on 8-bit values only, which still
> keeps sparse happy without an accidental promotion to a 32 bit integer.
>
> The reason the warning was occurring is because certain bitmasks that
> end with a mask next to a natural boundary like 7, 15, 23, 31, end up
> with a mask like 0x7f, which then results in sign extension when doing
> an invert (but I'm not a compiler expert). It was really only
> "clear_bit" that was having problems, and it was only on bit checks next
> to a byte boundary (top bit).
I guess this describes it incorrectly.
The problem is integer promotion of negation operation for any bit basically.
For example, if we have bit 3 (nr = 3) and got it in the clear bit we will
get (according to what I see in the warnings) 0xfffffff7. Which is simple
~(1 << 3) promoted to integer.
I think it is a C standard which dictates this, compiler just follows.
> Verified with a test module (see next patch) and assembly inspection
> that the patch doesn't introduce any change in generated code.
>
> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> ---
> v5: changed code to use simple AND and XOR, updated commit message
> v4: reverse argument order as suggested by David Laight, added reviewed-by
> v3: Clean up the header file changes as per peterz.
> v2: use correct CC: list
> ---
> arch/x86/include/asm/bitops.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
> index 062cdecb2f24..53f246e9df5a 100644
> --- a/arch/x86/include/asm/bitops.h
> +++ b/arch/x86/include/asm/bitops.h
> @@ -54,7 +54,7 @@ arch_set_bit(long nr, volatile unsigned long *addr)
> if (__builtin_constant_p(nr)) {
> asm volatile(LOCK_PREFIX "orb %1,%0"
> : CONST_MASK_ADDR(nr, addr)
> - : "iq" ((u8)CONST_MASK(nr))
> + : "iq" (CONST_MASK(nr) & 0xff)
> : "memory");
> } else {
> asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0"
> @@ -74,7 +74,7 @@ arch_clear_bit(long nr, volatile unsigned long *addr)
> if (__builtin_constant_p(nr)) {
> asm volatile(LOCK_PREFIX "andb %1,%0"
> : CONST_MASK_ADDR(nr, addr)
> - : "iq" ((u8)~CONST_MASK(nr)));
> + : "iq" (CONST_MASK(nr) ^ 0xff));
> } else {
> asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0"
> : : RLONG_ADDR(addr), "Ir" (nr) : "memory");
>
> base-commit: ca7e1fd1026c5af6a533b4b5447e1d2f153e28f2
> --
> 2.24.1
>
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply [flat|nested] 6+ messages in thread