[PATCH v2 07/10] : Add support for architecture-specific functions

George Spelvin
2016-05-27T15:03:18Z

This is just the infrastructure; there are no users yet.

This is modelled on CONFIG_ARCH_RANDOM; a CONFIG_ symbol declares
the existence of <asm/hash.h>.

That file may define its own versions of various functions, and define
HAVE_* symbols (no CONFIG_ prefix!) to suppress the generic ones.

Included is a self-test (in lib/test_hash.c) that verifies the basics.
It is NOT in general required that the arch-specific functions compute
the same thing as the generic, but if a HAVE_* symbol is defined with
the value 1, then equality is tested.

Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Cc: Philippe De Muyter <phdm@macq.eu>
Cc: linux-m68k@lists.linux-m68k.org
Cc: Alistair Francis <alistai@xilinx.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: uclinux-h8-devel@lists.sourceforge.jp
---
arch/Kconfig | 8 ++
fs/namei.c | 6 +-
include/linux/hash.h | 24 ++++-
lib/Kconfig.debug | 11 +++
lib/Makefile | 1 +
lib/test_hash.c | 250 +++++++++++++++++++++++++++++++++++++++++++++++++++
6 files changed, 296 insertions(+), 4 deletions(-)
create mode 100644 lib/test_hash.c

diff --git a/arch/Kconfig b/arch/Kconfig
index 81869a5e..96406e4d 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -589,6 +589,14 @@ config HAVE_STACK_VALIDATION
Architecture supports the 'objtool check' host tool command, which
performs compile-time stack metadata validation.

+config HAVE_ARCH_HASH
+ bool
+ default n
+ help
+ If this is set, the architecture provides an <asm/hash.h>
+ file which provides platform-specific implementations of some
+ functions in <linux/hash.h> or fs/namei.c.
+
#
# ABI hall of shame
#
diff --git a/fs/namei.c b/fs/namei.c
index 2b8d0650..cb438b84 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1788,7 +1788,11 @@ static int walk_component(struct nameidata *nd, int flags)

#include <asm/word-at-a-time.h>

-#ifdef CONFIG_64BIT
+#ifdef HASH_MIX
+
+/* Architecture provides HASH_MIX and fold_hash() in <asm/hash.h> */
+
+#elif defined(CONFIG_64BIT)
/*
* Register pressure in the mixing function is an issue, particularly
* on 32-bit x86, but almost any function requires one state value and
diff --git a/include/linux/hash.h b/include/linux/hash.h
index 8926f369..ab62a9a4 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -41,18 +41,36 @@
#define GOLDEN_RATIO_32 0x61C88647
#define GOLDEN_RATIO_64 0x61C8864680B583EBull

-static inline u32 __hash_32(u32 val)
+#ifdef CONFIG_HAVE_ARCH_HASH
+/* This header may use the GOLDEN_RATIO_xx constants */
+#include <asm/hash.h>
+#endif
+
+/*
+ * The _generic versions exist only so lib/test_hash.c can
+ * compare the arch-optimized versions with the generic.
+ */
+#ifndef HAVE_ARCH__HASH_32
+#define __hash_32 __hash_32_generic
+#endif
+static inline u32 __hash_32_generic(u32 val)
{
return val * GOLDEN_RATIO_32;
}

-static inline u32 hash_32(u32 val, unsigned int bits)
+#ifndef HAVE_ARCH_HASH_32
+#define hash_32 hash_32_generic
+#endif
+static inline u32 hash_32_generic(u32 val, unsigned int bits)
{
/* High bits are more random, so use them. */
return __hash_32(val) >> (32 - bits);
}

-static __always_inline u32 hash_64(u64 val, unsigned int bits)
+#ifndef HAVE_ARCH_HASH_64
+#define hash_64 hash_64_generic
+#endif
+static __always_inline u32 hash_64_generic(u64 val, unsigned int bits)
{
if (__builtin_constant_p(bits > 32 || bits == 0)) {
BUILD_BUG_ON(bits > 32 || bits == 0);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1e9a6075..18ec69ba 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1815,6 +1815,17 @@ config TEST_RHASHTABLE

If unsure, say N.

+config TEST_HASH
+ tristate "Perform selftest on hash functions"
+ default n
+ help
+ Enable this option to test the kernel's integer (<linux/hash,h>)
+ and string (<linux/stringhash.h>) hash functions on boot
+ (or module load).
+
+ This is intended to help people writing architecture-specific
+ optimized versions. If unsure, say N.
+
endmenu # runtime tests

config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index 9d9804e5..16c3bda5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -48,6 +48,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
obj-y += kstrtox.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
+obj-$(CONFIG_TEST_HASH) += test_hash.o
obj-$(CONFIG_TEST_KASAN) += test_kasan.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
obj-$(CONFIG_TEST_LKM) += test_module.o
diff --git a/lib/test_hash.c b/lib/test_hash.c
new file mode 100644
index 00000000..bb43dac1
--- /dev/null
+++ b/lib/test_hash.c
@@ -0,0 +1,250 @@
+/*
+ * Test cases for <linux/hash.h> and <linux/stringhash.h>
+ * This just verifies that various ways of computing a hash
+ * produce the same thing and, for cases where a k-bit hash
+ * value is requested, is of the requested size.
+ *
+ * We fill a buffer with a 255-byte null-terminated string,
+ * and use both full_name_hash() and hash_string() to hash the
+ * substrings from i to j, where 0 <= i < j < 256.
+ *
+ * The returned values are used to check that __hash_32() and
+ * __hash_32_generic() compute the same thing. Likewise hash_32()
+ * and hash_64().
+ * */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt "\n"
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/hash.h>
+#include <linux/stringhash.h>
+#include <linux/printk.h>
+
+/* 32-bit XORSHIFT generator. Seed must not be zero. */
+static u32 __init __attribute_const__
+xorshift(u32 seed)
+{
+ seed ^= seed << 13;
+ seed ^= seed >> 17;
+ seed ^= seed << 5;
+ return seed;
+}
+
+/* Given a non-zero x, returns a non-zero byte. */
+static u8 __init __attribute_const__
+mod255(u32 x)
+{
+ x = (x & 0xffff) + (x >> 16); /* 1 <= x <= 0x1fffe */
+ x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0x2fd */
+ x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0x100 */
+ x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0xff */
+ return x;
+}
+
+/* Fill the buffer with non-zero bytes. */
+static void __init
+fill_buf(char *buf, size_t len, u32 seed)
+{
+ size_t i;
+
+ for (i = 0; i < len; i++) {
+ seed = xorshift(seed);
+ buf[i] = mod255(seed);
+ }
+}
+
+/*
+ * Test the various integer hash functions. h64 (or its low-order bits)
+ * is the integer to hash. hash_or accumulates the OR of the hash values,
+ * which are later checked to see that they cover all the requested bits.
+ *
+ * Because these functions (as opposed to the string hashes) are all
+ * inline, the code being tested is actually in the module, and you can
+ * recompile and re-test the module without rebooting.
+ */
+static bool __init
+test_int_hash(unsigned long long h64, u32 hash_or[2][33])
+{
+ int k;
+ u32 h0 = (u32)h64, h1, h2;
+
+ /* Test __hash32 */
+ hash_or[0][0] |= h1 = __hash_32(h0);
+#ifdef HAVE_ARCH__HASH_32
+ hash_or[1][0] |= h2 = __hash_32_generic(h0);
+#if HAVE_ARCH__HASH_32 == 1
+ if (h1 != h2) {
+ pr_err("__hash_32(%#x) = %#x != __hash_32_generic() = %#x",
+ h0, h1, h2);
+ return false;
+ }
+#endif
+#endif
+
+ /* Test k = 1..32 bits */
+ for (k = 1; k <= 32; k++) {
+ u32 const m = ((u32)2 << (k-1)) - 1; /* Low k bits set */
+
+ /* Test hash_32 */
+ hash_or[0][k] |= h1 = hash_32(h0, k);
+ if (h1 > m) {
+ pr_err("hash_32(%#x, %d) = %#x > %#x", h0, k, h1, m);
+ return false;
+ }
+#ifdef HAVE_ARCH_HASH_32
+ h2 = hash_32_generic(h0, k);
+#if HAVE_ARCH_HASH_32 == 1
+ if (h1 != h2) {
+ pr_err("hash_32(%#x, %d) = %#x != hash_32_generic() "
+ " = %#x", h0, k, h1, h2);
+ return false;
+ }
+#else
+ if (h2 > m) {
+ pr_err("hash_32_generic(%#x, %d) = %#x > %#x",
+ h0, k, h1, m);
+ return false;
+ }
+#endif
+#endif
+ /* Test hash_64 */
+ hash_or[1][k] |= h1 = hash_64(h64, k);
+ if (h1 > m) {
+ pr_err("hash_64(%#llx, %d) = %#x > %#x", h64, k, h1, m);
+ return false;
+ }
+#ifdef HAVE_ARCH_HASH_64
+ h2 = hash_64_generic(h64, k);
+#if HAVE_ARCH_HASH_64 == 1
+ if (h1 != h2) {
+ pr_err("hash_64(%#llx, %d) = %#x != hash_64_generic() "
+ "= %#x", h64, k, h1, h2);
+ return false;
+ }
+#else
+ if (h2 > m) {
+ pr_err("hash_64_generic(%#llx, %d) = %#x > %#x",
+ h64, k, h1, m);
+ return false;
+ }
+#endif
+#endif
+ }
+
+ (void)h2; /* Suppress unused variable warning */
+ return true;
+}
+
+#define SIZE 256 /* Run time is cubic in SIZE */
+
+static int __init
+test_hash_init(void)
+{
+ char buf[SIZE];
+ u32 string_or = 0, hash_or[2][33] = { 0 };
+ unsigned tests = 0;
+ unsigned long long h64 = 0;
+ int i, j;
+
+ fill_buf(buf, SIZE-1, 1);
+
+ /* Test every possible non-empty substring in the buffer. */
+ for (j = SIZE; j > 0; --j) {
+ buf[j-1] = '\0';
+
+ for (i = 0; i < j; i++) {
+ u32 h0 = full_name_hash(buf+i, j-i);
+ u64 hashlen = hash_string(buf+i);
+
+ /* Check that hash_string gets the length right */
+ if (hashlen_len(hashlen) != j-i-1) {
+ pr_err("hash_string(%d..%d) returned length "
+ "%u, expected %d",
+ i, j, hashlen_len(hashlen), j-i-1);
+ return -EINVAL;
+ }
+ /* Check that the hashes match */
+ if (hashlen_hash(hashlen) != h0) {
+ pr_err("hash_string(%d..%d) = %08x != "
+ "full_name_hash() = %08x",
+ i, j, hashlen_hash(hashlen), h0);
+ return -EINVAL;
+ }
+
+ string_or |= h0;
+ h64 = h64 << 32 | h0; /* For use with hash_64 */
+ if (!test_int_hash(h64, hash_or))
+ return -EINVAL;
+ tests++;
+ } /* i */
+ } /* j */
+
+ /* The OR of all the hash values should cover all the bits */
+ if (~string_or) {
+ pr_err("OR of all string hash results = %#x != %#x",
+ string_or, -1u);
+ return -EINVAL;
+ }
+ if (~hash_or[0][0]) {
+ pr_err("OR of all __hash_32 results = %#x != %#x",
+ hash_or[0][0], -1u);
+ return -EINVAL;
+ }
+#ifdef HAVE_ARCH__HASH_32
+#if HAVE_ARCH__HASH_32 != 1 /* Test is pointless if results match */
+ if (~hash_or[1][0]) {
+ pr_err("OR of all __hash_32_generic results = %#x != %#x",
+ hash_or[1][0], -1u);
+ return -EINVAL;
+ }
+#endif
+#endif
+
+ /* Likewise for all the i-bit hash values */
+ for (i = 1; i <= 32; i++) {
+ u32 const m = ((u32)2 << (i-1)) - 1; /* Low i bits set */
+
+ if (hash_or[0][i] != m) {
+ pr_err("OR of all hash_32(%d) results = %#x "
+ "(%#x expected)", i, hash_or[0][i], m);
+ return -EINVAL;
+ }
+ if (hash_or[1][i] != m) {
+ pr_err("OR of all hash_64(%d) results = %#x "
+ "(%#x expected)", i, hash_or[1][i], m);
+ return -EINVAL;
+ }
+ }
+
+ /* Issue notices about skipped tests. */
+#ifndef HAVE_ARCH__HASH_32
+ pr_info("__hash_32() has no arch implementation to test.");
+#elif HAVE_ARCH__HASH_32 != 1
+ pr_info("__hash_32() is arch-specific; not compared to generic.");
+#endif
+#ifndef HAVE_ARCH_HASH_32
+ pr_info("hash_32() has no arch implementation to test.");
+#elif HAVE_ARCH_HASH_32 != 1
+ pr_info("hash_32() is arch-specific; not compared to generic.");
+#endif
+#ifndef HAVE_ARCH_HASH_64
+ pr_info("hash_64() has no arch implementation to test.");
+#elif HAVE_ARCH_HASH_64 != 1
+ pr_info("hash_64() is arch-specific; not compared to generic.");
+#endif
+
+ pr_notice("%u tests passed.", tests);
+
+ return 0;
+}
+
+static void __exit test_hash_exit(void)
+{
+}
+
+module_init(test_hash_init); /* Does everything */
+module_exit(test_hash_exit); /* Does nothing */
+
+MODULE_LICENSE("GPL");
--
2.8.1