[bitops] Add generic atomic bit test, set, and clear functions

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/include/bits/bitops.h

@@ -0,0 +1,94 @@
+#ifndef _BITS_BITOPS_H
+#define _BITS_BITOPS_H
+
+/** @file
+ *
+ * x86 bit operations
+ *
+ * We perform atomic bit set and bit clear operations using "lock bts"
+ * and "lock btr".  We use the output constraint to inform the
+ * compiler that any memory from the start of the bit field up to and
+ * including the byte containing the bit may be modified.  (This is
+ * overkill but shouldn't matter in practice since we're unlikely to
+ * subsequently read other bits from the same bit field.)
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdint.h>
+
+/**
+ * Set bit atomically
+ *
+ * @v bit		Bit to set
+ * @v bits		Bit field
+ */
+static inline __attribute__ (( always_inline )) void
+set_bit ( unsigned int bit, volatile void *bits ) {
+	volatile struct {
+		uint8_t byte[ ( bit / 8 ) + 1 ];
+	} *bytes = bits;
+
+	__asm__ __volatile__ ( "lock bts %1, %0"
+			       : "+m" ( *bytes ) : "Ir" ( bit ) );
+}
+
+/**
+ * Clear bit atomically
+ *
+ * @v bit		Bit to set
+ * @v bits		Bit field
+ */
+static inline __attribute__ (( always_inline )) void
+clear_bit ( unsigned int bit, volatile void *bits ) {
+	volatile struct {
+		uint8_t byte[ ( bit / 8 ) + 1 ];
+	} *bytes = bits;
+
+	__asm__ __volatile__ ( "lock btr %1, %0"
+			       : "+m" ( *bytes ) : "Ir" ( bit ) );
+}
+
+/**
+ * Test and set bit atomically
+ *
+ * @v bit		Bit to set
+ * @v bits		Bit field
+ * @ret old		Old value of bit (zero or non-zero)
+ */
+static inline __attribute__ (( always_inline )) int
+test_and_set_bit ( unsigned int bit, volatile void *bits ) {
+	volatile struct {
+		uint8_t byte[ ( bit / 8 ) + 1 ];
+	} *bytes = bits;
+	int old;
+
+	__asm__ __volatile__ ( "lock bts %2, %0\n\t"
+			       "sbb %1, %1\n\t"
+			       : "+m" ( *bytes ), "=r"  ( old )
+			       : "Ir" ( bit ) );
+	return old;
+}
+
+/**
+ * Test and clear bit atomically
+ *
+ * @v bit		Bit to set
+ * @v bits		Bit field
+ * @ret old		Old value of bit (zero or non-zero)
+ */
+static inline __attribute__ (( always_inline )) int
+test_and_clear_bit ( unsigned int bit, volatile void *bits ) {
+	volatile struct {
+		uint8_t byte[ ( bit / 8 ) + 1 ];
+	} *bytes = bits;
+	int old;
+
+	__asm__ __volatile__ ( "lock btr %2, %0\n\t"
+			       "sbb %1, %1\n\t"
+			       : "+m" ( *bytes ), "=r"  ( old )
+			       : "Ir" ( bit ) );
+	return old;
+}
+
+#endif /* _BITS_BITOPS_H */

src/include/ipxe/bitops.h

@@ -0,0 +1,19 @@
+#ifndef _IPXE_BITOPS_H
+#define _IPXE_BITOPS_H
+
+/** @file
+ *
+ * Bit operations
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <bits/bitops.h>
+
+void set_bit ( unsigned int bit, volatile void *bits );
+void clear_bit ( unsigned int bit, volatile void *bits );
+int test_and_set_bit ( unsigned int bit, volatile void *bits );
+int test_and_clear_bit ( unsigned int bit, volatile void *bits );
+
+#endif /* _IPXE_BITOPS_H */

src/tests/bitops_test.c

@@ -0,0 +1,102 @@
+/*
+ * Copyright (C) 2016 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/** @file
+ *
+ * Bit operations self-tests
+ *
+ */
+
+/* Forcibly enable assertions */
+#undef NDEBUG
+
+#include <stdint.h>
+#include <string.h>
+#include <assert.h>
+#include <ipxe/bitops.h>
+#include <ipxe/test.h>
+
+/**
+ * Perform bit operations self-tests
+ *
+ */
+static void bitops_test_exec ( void ) {
+	uint8_t bits[32];
+
+	/* Initialise bits */
+	memset ( bits, 0, sizeof ( bits ) );
+
+	/* Test set_bit() */
+	set_bit ( 0, bits );
+	ok ( bits[0] == 0x01 );
+	set_bit ( 17, bits );
+	ok ( bits[2] == 0x02 );
+	set_bit ( 22, bits );
+	ok ( bits[2] == 0x42 );
+	set_bit ( 22, bits );
+	ok ( bits[2] == 0x42 );
+
+	/* Test clear_bit() */
+	clear_bit ( 0, bits );
+	ok ( bits[5] == 0x00 );
+	bits[5] = 0xff;
+	clear_bit ( 42, bits );
+	ok ( bits[5] == 0xfb );
+	clear_bit ( 42, bits );
+	ok ( bits[5] == 0xfb );
+	clear_bit ( 44, bits );
+	ok ( bits[5] == 0xeb );
+
+	/* Test test_and_set_bit() */
+	ok ( test_and_set_bit ( 0, bits ) == 0 );
+	ok ( bits[0] == 0x01 );
+	ok ( test_and_set_bit ( 0, bits ) != 0 );
+	ok ( bits[0] == 0x01 );
+	ok ( test_and_set_bit ( 69, bits ) == 0 );
+	ok ( bits[8] == 0x20 );
+	ok ( test_and_set_bit ( 69, bits ) != 0 );
+	ok ( bits[8] == 0x20 );
+	ok ( test_and_set_bit ( 69, bits ) != 0 );
+	ok ( bits[8] == 0x20 );
+
+	/* Test test_and_clear_bit() */
+	ok ( test_and_clear_bit ( 0, bits ) != 0 );
+	ok ( bits[0] == 0x00 );
+	ok ( test_and_clear_bit ( 0, bits ) == 0 );
+	ok ( bits[0] == 0x00 );
+	bits[31] = 0xeb;
+	ok ( test_and_clear_bit ( 255, bits ) != 0 );
+	ok ( bits[31] == 0x6b );
+	ok ( test_and_clear_bit ( 255, bits ) == 0 );
+	ok ( bits[31] == 0x6b );
+	ok ( test_and_clear_bit ( 255, bits ) == 0 );
+	ok ( bits[31] == 0x6b );
+}
+
+/** Bit operations self-test */
+struct self_test bitops_test __self_test = {
+	.name = "bitops",
+	.exec = bitops_test_exec,
+};

src/tests/tests.c

@@ -68,3 +68,4 @@ REQUIRE_OBJECT ( setjmp_test );
 REQUIRE_OBJECT ( pccrc_test );
 REQUIRE_OBJECT ( linebuf_test );
 REQUIRE_OBJECT ( iobuf_test );
+REQUIRE_OBJECT ( bitops_test );