Merge branch 'x86/hyperv' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Topic branch for stable KVM clockource under Hyper-V.

Thanks to Christoffer Dall for resolving the ARM conflict.

19 files changed, 228 insertions, 47 deletions

diff --git a/arch/xtensa/include/asm/asmmacro.h b/arch/xtensa/include/asm/asmmacro.h
index 746dcc8b5abc..7f2ae5872151 100644
--- a/arch/xtensa/include/asm/asmmacro.h
+++ b/arch/xtensa/include/asm/asmmacro.h
@@ -150,5 +150,45 @@
 		__endl	\ar \as
 	.endm
 
+/* Load or store instructions that may cause exceptions use the EX macro. */
+
+#define EX(handler)				\
+	.section __ex_table, "a";		\
+	.word	97f, handler;			\
+	.previous				\
+97:
+
+
+/*
+ * Extract unaligned word that is split between two registers w0 and w1
+ * into r regardless of machine endianness. SAR must be loaded with the
+ * starting bit of the word (see __ssa8).
+ */
+
+	.macro __src_b	r, w0, w1
+#ifdef __XTENSA_EB__
+		src	\r, \w0, \w1
+#else
+		src	\r, \w1, \w0
+#endif
+	.endm
+
+/*
+ * Load 2 lowest address bits of r into SAR for __src_b to extract unaligned
+ * word starting at r from two registers loaded from consecutive aligned
+ * addresses covering r regardless of machine endianness.
+ *
+ *      r   0   1   2   3
+ * LE SAR   0   8  16  24
+ * BE SAR  32  24  16   8
+ */
+
+	.macro __ssa8	r
+#ifdef __XTENSA_EB__
+		ssa8b	\r
+#else
+		ssa8l	\r
+#endif
+	.endm
 
 #endif /* _XTENSA_ASMMACRO_H */
diff --git a/arch/xtensa/include/asm/current.h b/arch/xtensa/include/asm/current.h
index 47e46dcf5d49..5d98a7ad4251 100644
--- a/arch/xtensa/include/asm/current.h
+++ b/arch/xtensa/include/asm/current.h
@@ -11,6 +11,8 @@
 #ifndef _XTENSA_CURRENT_H
 #define _XTENSA_CURRENT_H
 
+#include <asm/thread_info.h>
+
 #ifndef __ASSEMBLY__
 
 #include <linux/thread_info.h>
@@ -26,8 +28,6 @@ static inline struct task_struct *get_current(void)
 
 #else
 
-#define CURRENT_SHIFT 13
-
 #define GET_CURRENT(reg,sp)		\
 	GET_THREAD_INFO(reg,sp);	\
 	l32i reg, reg, TI_TASK		\
diff --git a/arch/xtensa/include/asm/fixmap.h b/arch/xtensa/include/asm/fixmap.h
index 0d30403b6c95..7e25c1b50ac0 100644
--- a/arch/xtensa/include/asm/fixmap.h
+++ b/arch/xtensa/include/asm/fixmap.h
@@ -44,7 +44,7 @@ enum fixed_addresses {
 	__end_of_fixed_addresses
 };
 
-#define FIXADDR_TOP     (VMALLOC_START - PAGE_SIZE)
+#define FIXADDR_TOP     (XCHAL_KSEG_CACHED_VADDR - PAGE_SIZE)
 #define FIXADDR_SIZE	(__end_of_fixed_addresses << PAGE_SHIFT)
 #define FIXADDR_START	((FIXADDR_TOP - FIXADDR_SIZE) & PMD_MASK)
 
@@ -63,7 +63,7 @@ static __always_inline unsigned long fix_to_virt(const unsigned int idx)
 	 * table.
 	 */
 	BUILD_BUG_ON(FIXADDR_START <
-		     XCHAL_PAGE_TABLE_VADDR + XCHAL_PAGE_TABLE_SIZE);
+		     TLBTEMP_BASE_1 + TLBTEMP_SIZE);
 	BUILD_BUG_ON(idx >= __end_of_fixed_addresses);
 	return __fix_to_virt(idx);
 }
diff --git a/arch/xtensa/include/asm/futex.h b/arch/xtensa/include/asm/futex.h
index eaaf1ebcc7a4..5bfbc1c401d4 100644
--- a/arch/xtensa/include/asm/futex.h
+++ b/arch/xtensa/include/asm/futex.h
@@ -92,7 +92,6 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 			      u32 oldval, u32 newval)
 {
 	int ret = 0;
-	u32 prev;
 
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
 		return -EFAULT;
@@ -103,26 +102,24 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 
 	__asm__ __volatile__ (
 	"	# futex_atomic_cmpxchg_inatomic\n"
-	"1:	l32i	%1, %3, 0\n"
-	"	mov	%0, %5\n"
-	"	wsr	%1, scompare1\n"
-	"2:	s32c1i	%0, %3, 0\n"
-	"3:\n"
+	"	wsr	%5, scompare1\n"
+	"1:	s32c1i	%1, %4, 0\n"
+	"	s32i	%1, %6, 0\n"
+	"2:\n"
 	"	.section .fixup,\"ax\"\n"
 	"	.align 4\n"
-	"4:	.long	3b\n"
-	"5:	l32r	%1, 4b\n"
-	"	movi	%0, %6\n"
+	"3:	.long	2b\n"
+	"4:	l32r	%1, 3b\n"
+	"	movi	%0, %7\n"
 	"	jx	%1\n"
 	"	.previous\n"
 	"	.section __ex_table,\"a\"\n"
-	"	.long 1b,5b,2b,5b\n"
+	"	.long 1b,4b\n"
 	"	.previous\n"
-	: "+r" (ret), "=&r" (prev), "+m" (*uaddr)
-	: "r" (uaddr), "r" (oldval), "r" (newval), "I" (-EFAULT)
+	: "+r" (ret), "+r" (newval), "+m" (*uaddr), "+m" (*uval)
+	: "r" (uaddr), "r" (oldval), "r" (uval), "I" (-EFAULT)
 	: "memory");
 
-	*uval = prev;
 	return ret;
 }
 
diff --git a/arch/xtensa/include/asm/highmem.h b/arch/xtensa/include/asm/highmem.h
index 6e070db1022e..04e9340eac4b 100644
--- a/arch/xtensa/include/asm/highmem.h
+++ b/arch/xtensa/include/asm/highmem.h
@@ -72,7 +72,7 @@ static inline void *kmap(struct page *page)
 	 * page table.
 	 */
 	BUILD_BUG_ON(PKMAP_BASE <
-		     XCHAL_PAGE_TABLE_VADDR + XCHAL_PAGE_TABLE_SIZE);
+		     TLBTEMP_BASE_1 + TLBTEMP_SIZE);
 	BUG_ON(in_interrupt());
 	if (!PageHighMem(page))
 		return page_address(page);
diff --git a/arch/xtensa/include/asm/kasan.h b/arch/xtensa/include/asm/kasan.h
new file mode 100644
index 000000000000..54be80876e57
--- /dev/null
+++ b/arch/xtensa/include/asm/kasan.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_KASAN_H
+#define __ASM_KASAN_H
+
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_KASAN
+
+#include <linux/kernel.h>
+#include <linux/sizes.h>
+#include <asm/kmem_layout.h>
+
+/* Start of area covered by KASAN */
+#define KASAN_START_VADDR __XTENSA_UL_CONST(0x90000000)
+/* Start of the shadow map */
+#define KASAN_SHADOW_START (XCHAL_PAGE_TABLE_VADDR + XCHAL_PAGE_TABLE_SIZE)
+/* Size of the shadow map */
+#define KASAN_SHADOW_SIZE (-KASAN_START_VADDR >> KASAN_SHADOW_SCALE_SHIFT)
+/* Offset for mem to shadow address transformation */
+#define KASAN_SHADOW_OFFSET __XTENSA_UL_CONST(CONFIG_KASAN_SHADOW_OFFSET)
+
+void __init kasan_early_init(void);
+void __init kasan_init(void);
+
+#else
+
+static inline void kasan_early_init(void)
+{
+}
+
+static inline void kasan_init(void)
+{
+}
+
+#endif
+#endif
+#endif
diff --git a/arch/xtensa/include/asm/kmem_layout.h b/arch/xtensa/include/asm/kmem_layout.h
index 561f8729bcde..2317c835a4db 100644
--- a/arch/xtensa/include/asm/kmem_layout.h
+++ b/arch/xtensa/include/asm/kmem_layout.h
@@ -71,4 +71,11 @@
 
 #endif
 
+#ifndef CONFIG_KASAN
+#define KERNEL_STACK_SHIFT	13
+#else
+#define KERNEL_STACK_SHIFT	15
+#endif
+#define KERNEL_STACK_SIZE	(1 << KERNEL_STACK_SHIFT)
+
 #endif
diff --git a/arch/xtensa/include/asm/linkage.h b/arch/xtensa/include/asm/linkage.h
new file mode 100644
index 000000000000..0ba9973235d9
--- /dev/null
+++ b/arch/xtensa/include/asm/linkage.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_LINKAGE_H
+#define __ASM_LINKAGE_H
+
+#define __ALIGN		.align 4
+#define __ALIGN_STR	".align 4"
+
+#endif
diff --git a/arch/xtensa/include/asm/mmu_context.h b/arch/xtensa/include/asm/mmu_context.h
index f7e186dfc4e4..de5e6cbbafe4 100644
--- a/arch/xtensa/include/asm/mmu_context.h
+++ b/arch/xtensa/include/asm/mmu_context.h
@@ -52,6 +52,7 @@ DECLARE_PER_CPU(unsigned long, asid_cache);
 #define ASID_INSERT(x)	(0x03020001 | (((x) & ASID_MASK) << 8))
 
 void init_mmu(void);
+void init_kio(void);
 
 static inline void set_rasid_register (unsigned long val)
 {
diff --git a/arch/xtensa/include/asm/nommu_context.h b/arch/xtensa/include/asm/nommu_context.h
index 2cebdbbdb633..37251b2ef871 100644
--- a/arch/xtensa/include/asm/nommu_context.h
+++ b/arch/xtensa/include/asm/nommu_context.h
@@ -3,6 +3,10 @@ static inline void init_mmu(void)
 {
 }
 
+static inline void init_kio(void)
+{
+}
+
 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
 {
 }
diff --git a/arch/xtensa/include/asm/page.h b/arch/xtensa/include/asm/page.h
index 4ddbfd57a7c8..5d69c11c01b8 100644
--- a/arch/xtensa/include/asm/page.h
+++ b/arch/xtensa/include/asm/page.h
@@ -36,8 +36,6 @@
 #define MAX_LOW_PFN	PHYS_PFN(0xfffffffful)
 #endif
 
-#define PGTABLE_START	0x80000000
-
 /*
  * Cache aliasing:
  *
diff --git a/arch/xtensa/include/asm/pgtable.h b/arch/xtensa/include/asm/pgtable.h
index 30dd5b2e4ad5..38802259978f 100644
--- a/arch/xtensa/include/asm/pgtable.h
+++ b/arch/xtensa/include/asm/pgtable.h
@@ -12,9 +12,9 @@
 #define _XTENSA_PGTABLE_H
 
 #define __ARCH_USE_5LEVEL_HACK
-#include <asm-generic/pgtable-nopmd.h>
 #include <asm/page.h>
 #include <asm/kmem_layout.h>
+#include <asm-generic/pgtable-nopmd.h>
 
 /*
  * We only use two ring levels, user and kernel space.
@@ -170,6 +170,7 @@
 #define PAGE_SHARED_EXEC \
 	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_WRITABLE | _PAGE_HW_EXEC)
 #define PAGE_KERNEL	   __pgprot(_PAGE_PRESENT | _PAGE_HW_WRITE)
+#define PAGE_KERNEL_RO	   __pgprot(_PAGE_PRESENT)
 #define PAGE_KERNEL_EXEC   __pgprot(_PAGE_PRESENT|_PAGE_HW_WRITE|_PAGE_HW_EXEC)
 
 #if (DCACHE_WAY_SIZE > PAGE_SIZE)
diff --git a/arch/xtensa/include/asm/ptrace.h b/arch/xtensa/include/asm/ptrace.h
index e2d9c5eb10bd..3a5c5918aea3 100644
--- a/arch/xtensa/include/asm/ptrace.h
+++ b/arch/xtensa/include/asm/ptrace.h
@@ -10,6 +10,7 @@
 #ifndef _XTENSA_PTRACE_H
 #define _XTENSA_PTRACE_H
 
+#include <asm/kmem_layout.h>
 #include <uapi/asm/ptrace.h>
 
 /*
@@ -38,20 +39,6 @@
  *		+-----------------------+ --------
  */
 
-#define KERNEL_STACK_SIZE (2 * PAGE_SIZE)
-
-/*  Offsets for exception_handlers[] (3 x 64-entries x 4-byte tables). */
-
-#define EXC_TABLE_KSTK		0x004	/* Kernel Stack */
-#define EXC_TABLE_DOUBLE_SAVE	0x008	/* Double exception save area for a0 */
-#define EXC_TABLE_FIXUP		0x00c	/* Fixup handler */
-#define EXC_TABLE_PARAM		0x010	/* For passing a parameter to fixup */
-#define EXC_TABLE_SYSCALL_SAVE	0x014	/* For fast syscall handler */
-#define EXC_TABLE_FAST_USER	0x100	/* Fast user exception handler */
-#define EXC_TABLE_FAST_KERNEL	0x200	/* Fast kernel exception handler */
-#define EXC_TABLE_DEFAULT	0x300	/* Default C-Handler */
-#define EXC_TABLE_SIZE		0x400
-
 #ifndef __ASSEMBLY__
 
 #include <asm/coprocessor.h>
diff --git a/arch/xtensa/include/asm/regs.h b/arch/xtensa/include/asm/regs.h
index 881a1134a4b4..477594e5817f 100644
--- a/arch/xtensa/include/asm/regs.h
+++ b/arch/xtensa/include/asm/regs.h
@@ -76,6 +76,7 @@
 #define EXCCAUSE_COPROCESSOR5_DISABLED		37
 #define EXCCAUSE_COPROCESSOR6_DISABLED		38
 #define EXCCAUSE_COPROCESSOR7_DISABLED		39
+#define EXCCAUSE_N				64
 
 /*  PS register fields.  */
 
diff --git a/arch/xtensa/include/asm/stackprotector.h b/arch/xtensa/include/asm/stackprotector.h
new file mode 100644
index 000000000000..e368f94fd2af
--- /dev/null
+++ b/arch/xtensa/include/asm/stackprotector.h
@@ -0,0 +1,40 @@
+/*
+ * GCC stack protector support.
+ *
+ * (This is directly adopted from the ARM implementation)
+ *
+ * Stack protector works by putting predefined pattern at the start of
+ * the stack frame and verifying that it hasn't been overwritten when
+ * returning from the function.  The pattern is called stack canary
+ * and gcc expects it to be defined by a global variable called
+ * "__stack_chk_guard" on Xtensa.  This unfortunately means that on SMP
+ * we cannot have a different canary value per task.
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H 1
+
+#include <linux/random.h>
+#include <linux/version.h>
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * Initialize the stackprotector canary value.
+ *
+ * NOTE: this must only be called from functions that never return,
+ * and it must always be inlined.
+ */
+static __always_inline void boot_init_stack_canary(void)
+{
+	unsigned long canary;
+
+	/* Try to get a semi random initial value. */
+	get_random_bytes(&canary, sizeof(canary));
+	canary ^= LINUX_VERSION_CODE;
+
+	current->stack_canary = canary;
+	__stack_chk_guard = current->stack_canary;
+}
+
+#endif	/* _ASM_STACKPROTECTOR_H */
diff --git a/arch/xtensa/include/asm/string.h b/arch/xtensa/include/asm/string.h
index 8d5d9dfadb09..89b51a0c752f 100644
--- a/arch/xtensa/include/asm/string.h
+++ b/arch/xtensa/include/asm/string.h
@@ -53,7 +53,7 @@ static inline char *strncpy(char *__dest, const char *__src, size_t __n)
 		"bne	%1, %5, 1b\n"
 		"2:"
 		: "=r" (__dest), "=r" (__src), "=&r" (__dummy)
-		: "0" (__dest), "1" (__src), "r" (__src+__n)
+		: "0" (__dest), "1" (__src), "r" ((uintptr_t)__src+__n)
 		: "memory");
 
 	return __xdest;
@@ -101,21 +101,40 @@ static inline int strncmp(const char *__cs, const char *__ct, size_t __n)
 		"2:\n\t"
 		"sub	%2, %2, %3"
 		: "=r" (__cs), "=r" (__ct), "=&r" (__res), "=&r" (__dummy)
-		: "0" (__cs), "1" (__ct), "r" (__cs+__n));
+		: "0" (__cs), "1" (__ct), "r" ((uintptr_t)__cs+__n));
 
 	return __res;
 }
 
 #define __HAVE_ARCH_MEMSET
 extern void *memset(void *__s, int __c, size_t __count);
+extern void *__memset(void *__s, int __c, size_t __count);
 
 #define __HAVE_ARCH_MEMCPY
 extern void *memcpy(void *__to, __const__ void *__from, size_t __n);
+extern void *__memcpy(void *__to, __const__ void *__from, size_t __n);
 
 #define __HAVE_ARCH_MEMMOVE
 extern void *memmove(void *__dest, __const__ void *__src, size_t __n);
+extern void *__memmove(void *__dest, __const__ void *__src, size_t __n);
 
 /* Don't build bcopy at all ...  */
 #define __HAVE_ARCH_BCOPY
 
+#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
+
+/*
+ * For files that are not instrumented (e.g. mm/slub.c) we
+ * should use not instrumented version of mem* functions.
+ */
+
+#define memcpy(dst, src, len) __memcpy(dst, src, len)
+#define memmove(dst, src, len) __memmove(dst, src, len)
+#define memset(s, c, n) __memset(s, c, n)
+
+#ifndef __NO_FORTIFY
+#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
+#endif
+#endif
+
 #endif	/* _XTENSA_STRING_H */
diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
index 7be2400f745a..2bd19ae61e47 100644
--- a/arch/xtensa/include/asm/thread_info.h
+++ b/arch/xtensa/include/asm/thread_info.h
@@ -11,7 +11,9 @@
 #ifndef _XTENSA_THREAD_INFO_H
 #define _XTENSA_THREAD_INFO_H
 
-#ifdef __KERNEL__
+#include <asm/kmem_layout.h>
+
+#define CURRENT_SHIFT KERNEL_STACK_SHIFT
 
 #ifndef __ASSEMBLY__
 # include <asm/processor.h>
@@ -77,14 +79,11 @@ struct thread_info {
 	.addr_limit	= KERNEL_DS,		\
 }
 
-#define init_thread_info	(init_thread_union.thread_info)
-#define init_stack		(init_thread_union.stack)
-
 /* how to get the thread information struct from C */
 static inline struct thread_info *current_thread_info(void)
 {
 	struct thread_info *ti;
-	 __asm__("extui %0,a1,0,13\n\t"
+	 __asm__("extui %0, a1, 0, "__stringify(CURRENT_SHIFT)"\n\t"
 	         "xor %0, a1, %0" : "=&r" (ti) : );
 	return ti;
 }
@@ -93,7 +92,7 @@ static inline struct thread_info *current_thread_info(void)
 
 /* how to get the thread information struct from ASM */
 #define GET_THREAD_INFO(reg,sp) \
-	extui reg, sp, 0, 13; \
+	extui reg, sp, 0, CURRENT_SHIFT; \
 	xor   reg, sp, reg
 #endif
 
@@ -130,8 +129,7 @@ static inline struct thread_info *current_thread_info(void)
  */
 #define TS_USEDFPU		0x0001	/* FPU was used by this task this quantum (SMP) */
 
-#define THREAD_SIZE 8192	//(2*PAGE_SIZE)
-#define THREAD_SIZE_ORDER 1
+#define THREAD_SIZE KERNEL_STACK_SIZE
+#define THREAD_SIZE_ORDER (KERNEL_STACK_SHIFT - PAGE_SHIFT)
 
-#endif	/* __KERNEL__ */
 #endif	/* _XTENSA_THREAD_INFO */
diff --git a/arch/xtensa/include/asm/traps.h b/arch/xtensa/include/asm/traps.h
index 2e69aa4b843f..f5cd7a7e65e0 100644
--- a/arch/xtensa/include/asm/traps.h
+++ b/arch/xtensa/include/asm/traps.h
@@ -13,12 +13,47 @@
 #include <asm/ptrace.h>
 
 /*
+ * Per-CPU exception handling data structure.
+ * EXCSAVE1 points to it.
+ */
+struct exc_table {
+	/* Kernel Stack */
+	void *kstk;
+	/* Double exception save area for a0 */
+	unsigned long double_save;
+	/* Fixup handler */
+	void *fixup;
+	/* For passing a parameter to fixup */
+	void *fixup_param;
+	/* For fast syscall handler */
+	unsigned long syscall_save;
+	/* Fast user exception handlers */
+	void *fast_user_handler[EXCCAUSE_N];
+	/* Fast kernel exception handlers */
+	void *fast_kernel_handler[EXCCAUSE_N];
+	/* Default C-Handlers */
+	void *default_handler[EXCCAUSE_N];
+};
+
+/*
  * handler must be either of the following:
  *  void (*)(struct pt_regs *regs);
  *  void (*)(struct pt_regs *regs, unsigned long exccause);
  */
 extern void * __init trap_set_handler(int cause, void *handler);
 extern void do_unhandled(struct pt_regs *regs, unsigned long exccause);
+void fast_second_level_miss(void);
+
+/* Initialize minimal exc_table structure sufficient for basic paging */
+static inline void __init early_trap_init(void)
+{
+	static struct exc_table exc_table __initdata = {
+		.fast_kernel_handler[EXCCAUSE_DTLB_MISS] =
+			fast_second_level_miss,
+	};
+	__asm__ __volatile__("wsr  %0, excsave1\n" : : "a" (&exc_table));
+}
+
 void secondary_trap_init(void);
 
 static inline void spill_registers(void)
diff --git a/arch/xtensa/include/asm/uaccess.h b/arch/xtensa/include/asm/uaccess.h
index b8f152b6aaa5..f1158b4c629c 100644
--- a/arch/xtensa/include/asm/uaccess.h
+++ b/arch/xtensa/include/asm/uaccess.h
@@ -44,6 +44,8 @@
 #define __access_ok(addr, size) (__kernel_ok || __user_ok((addr), (size)))
 #define access_ok(type, addr, size) __access_ok((unsigned long)(addr), (size))
 
+#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
+
 /*
  * These are the main single-value transfer routines.  They
  * automatically use the right size if we just have the right pointer
@@ -261,7 +263,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 static inline unsigned long
 __xtensa_clear_user(void *addr, unsigned long size)
 {
-	if ( ! memset(addr, 0, size) )
+	if (!__memset(addr, 0, size))
 		return size;
 	return 0;
 }
@@ -277,6 +279,8 @@ clear_user(void *addr, unsigned long size)
 #define __clear_user  __xtensa_clear_user
 
 
+#ifndef CONFIG_GENERIC_STRNCPY_FROM_USER
+
 extern long __strncpy_user(char *, const char *, long);
 
 static inline long
@@ -286,6 +290,9 @@ strncpy_from_user(char *dst, const char *src, long count)
 		return __strncpy_user(dst, src, count);
 	return -EFAULT;
 }
+#else
+long strncpy_from_user(char *dst, const char *src, long count);
+#endif
 
 /*
  * Return the size of a string (including the ending 0!)