kdb: core for kgdb back end (1 of 2)

This patch contains only the kdb core.  Because the change set was
large, it was split.  The next patch in the series includes the
instrumentation into the core kernel which are mainly helper functions
for kdb.

This work is directly derived from kdb v4.4 found at:

ftp://oss.sgi.com/projects/kdb/download/v4.4/

The kdb internals have been re-organized to make them mostly platform
independent and to connect everything to the debug core which is used by
gdbstub (which has long been known as kgdb).

The original version of kdb was 58,000 lines worth of changes to
support x86.  From that implementation only the kdb shell, and basic
commands for memory access, runcontrol, lsmod, and dmesg where carried
forward.

This is a generic implementation which aims to cover all the current
architectures using the kgdb core: ppc, arm, x86, mips, sparc, sh and
blackfin.  More archictectures can be added by implementing the
architecture specific kgdb functions.

[mort@sgi.com: Compile fix with hugepages enabled]
[mort@sgi.com: Clean breakpoint code renaming kdba_ -> kdb_]
[mort@sgi.com: fix new line after printing registers]
[mort@sgi.com: Remove the concept of global vs. local breakpoints]
[mort@sgi.com: Rework kdb_si_swapinfo to use more generic name]
[mort@sgi.com: fix the information dump macros, remove 'arch' from the names]
[sfr@canb.auug.org.au: include fixup to include linux/slab.h]

CC: linux-arch@vger.kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Martin Hicks <mort@sgi.com>

1 files changed, 927 insertions, 0 deletions

diff --git a/kernel/debug/kdb/kdb_support.c b/kernel/debug/kdb/kdb_support.c
new file mode 100644
index 00000000000..45344d5c53d
--- /dev/null
+++ b/kernel/debug/kdb/kdb_support.c
@@ -0,0 +1,927 @@
+/*
+ * Kernel Debugger Architecture Independent Support Functions
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (c) 1999-2004 Silicon Graphics, Inc.  All Rights Reserved.
+ * Copyright (c) 2009 Wind River Systems, Inc.  All Rights Reserved.
+ * 03/02/13    added new 2.5 kallsyms <xavier.bru@bull.net>
+ */
+
+#include <stdarg.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/kallsyms.h>
+#include <linux/stddef.h>
+#include <linux/vmalloc.h>
+#include <linux/ptrace.h>
+#include <linux/module.h>
+#include <linux/highmem.h>
+#include <linux/hardirq.h>
+#include <linux/delay.h>
+#include <linux/uaccess.h>
+#include <linux/kdb.h>
+#include <linux/slab.h>
+#include "kdb_private.h"
+
+/*
+ * kdbgetsymval - Return the address of the given symbol.
+ *
+ * Parameters:
+ *	symname	Character string containing symbol name
+ *      symtab  Structure to receive results
+ * Returns:
+ *	0	Symbol not found, symtab zero filled
+ *	1	Symbol mapped to module/symbol/section, data in symtab
+ */
+int kdbgetsymval(const char *symname, kdb_symtab_t *symtab)
+{
+	if (KDB_DEBUG(AR))
+		kdb_printf("kdbgetsymval: symname=%s, symtab=%p\n", symname,
+			   symtab);
+	memset(symtab, 0, sizeof(*symtab));
+	symtab->sym_start = kallsyms_lookup_name(symname);
+	if (symtab->sym_start) {
+		if (KDB_DEBUG(AR))
+			kdb_printf("kdbgetsymval: returns 1, "
+				   "symtab->sym_start=0x%lx\n",
+				   symtab->sym_start);
+		return 1;
+	}
+	if (KDB_DEBUG(AR))
+		kdb_printf("kdbgetsymval: returns 0\n");
+	return 0;
+}
+EXPORT_SYMBOL(kdbgetsymval);
+
+static char *kdb_name_table[100];	/* arbitrary size */
+
+/*
+ * kdbnearsym -	Return the name of the symbol with the nearest address
+ *	less than 'addr'.
+ *
+ * Parameters:
+ *	addr	Address to check for symbol near
+ *	symtab  Structure to receive results
+ * Returns:
+ *	0	No sections contain this address, symtab zero filled
+ *	1	Address mapped to module/symbol/section, data in symtab
+ * Remarks:
+ *	2.6 kallsyms has a "feature" where it unpacks the name into a
+ *	string.  If that string is reused before the caller expects it
+ *	then the caller sees its string change without warning.  To
+ *	avoid cluttering up the main kdb code with lots of kdb_strdup,
+ *	tests and kfree calls, kdbnearsym maintains an LRU list of the
+ *	last few unique strings.  The list is sized large enough to
+ *	hold active strings, no kdb caller of kdbnearsym makes more
+ *	than ~20 later calls before using a saved value.
+ */
+int kdbnearsym(unsigned long addr, kdb_symtab_t *symtab)
+{
+	int ret = 0;
+	unsigned long symbolsize;
+	unsigned long offset;
+#define knt1_size 128		/* must be >= kallsyms table size */
+	char *knt1 = NULL;
+
+	if (KDB_DEBUG(AR))
+		kdb_printf("kdbnearsym: addr=0x%lx, symtab=%p\n", addr, symtab);
+	memset(symtab, 0, sizeof(*symtab));
+
+	if (addr < 4096)
+		goto out;
+	knt1 = debug_kmalloc(knt1_size, GFP_ATOMIC);
+	if (!knt1) {
+		kdb_printf("kdbnearsym: addr=0x%lx cannot kmalloc knt1\n",
+			   addr);
+		goto out;
+	}
+	symtab->sym_name = kallsyms_lookup(addr, &symbolsize , &offset,
+				(char **)(&symtab->mod_name), knt1);
+	if (offset > 8*1024*1024) {
+		symtab->sym_name = NULL;
+		addr = offset = symbolsize = 0;
+	}
+	symtab->sym_start = addr - offset;
+	symtab->sym_end = symtab->sym_start + symbolsize;
+	ret = symtab->sym_name != NULL && *(symtab->sym_name) != '\0';
+
+	if (ret) {
+		int i;
+		/* Another 2.6 kallsyms "feature".  Sometimes the sym_name is
+		 * set but the buffer passed into kallsyms_lookup is not used,
+		 * so it contains garbage.  The caller has to work out which
+		 * buffer needs to be saved.
+		 *
+		 * What was Rusty smoking when he wrote that code?
+		 */
+		if (symtab->sym_name != knt1) {
+			strncpy(knt1, symtab->sym_name, knt1_size);
+			knt1[knt1_size-1] = '\0';
+		}
+		for (i = 0; i < ARRAY_SIZE(kdb_name_table); ++i) {
+			if (kdb_name_table[i] &&
+			    strcmp(kdb_name_table[i], knt1) == 0)
+				break;
+		}
+		if (i >= ARRAY_SIZE(kdb_name_table)) {
+			debug_kfree(kdb_name_table[0]);
+			memcpy(kdb_name_table, kdb_name_table+1,
+			       sizeof(kdb_name_table[0]) *
+			       (ARRAY_SIZE(kdb_name_table)-1));
+		} else {
+			debug_kfree(knt1);
+			knt1 = kdb_name_table[i];
+			memcpy(kdb_name_table+i, kdb_name_table+i+1,
+			       sizeof(kdb_name_table[0]) *
+			       (ARRAY_SIZE(kdb_name_table)-i-1));
+		}
+		i = ARRAY_SIZE(kdb_name_table) - 1;
+		kdb_name_table[i] = knt1;
+		symtab->sym_name = kdb_name_table[i];
+		knt1 = NULL;
+	}
+
+	if (symtab->mod_name == NULL)
+		symtab->mod_name = "kernel";
+	if (KDB_DEBUG(AR))
+		kdb_printf("kdbnearsym: returns %d symtab->sym_start=0x%lx, "
+		   "symtab->mod_name=%p, symtab->sym_name=%p (%s)\n", ret,
+		   symtab->sym_start, symtab->mod_name, symtab->sym_name,
+		   symtab->sym_name);
+
+out:
+	debug_kfree(knt1);
+	return ret;
+}
+
+void kdbnearsym_cleanup(void)
+{
+	int i;
+	for (i = 0; i < ARRAY_SIZE(kdb_name_table); ++i) {
+		if (kdb_name_table[i]) {
+			debug_kfree(kdb_name_table[i]);
+			kdb_name_table[i] = NULL;
+		}
+	}
+}
+
+static char ks_namebuf[KSYM_NAME_LEN+1], ks_namebuf_prev[KSYM_NAME_LEN+1];
+
+/*
+ * kallsyms_symbol_complete
+ *
+ * Parameters:
+ *	prefix_name	prefix of a symbol name to lookup
+ *	max_len		maximum length that can be returned
+ * Returns:
+ *	Number of symbols which match the given prefix.
+ * Notes:
+ *	prefix_name is changed to contain the longest unique prefix that
+ *	starts with this prefix (tab completion).
+ */
+int kallsyms_symbol_complete(char *prefix_name, int max_len)
+{
+	loff_t pos = 0;
+	int prefix_len = strlen(prefix_name), prev_len = 0;
+	int i, number = 0;
+	const char *name;
+
+	while ((name = kdb_walk_kallsyms(&pos))) {
+		if (strncmp(name, prefix_name, prefix_len) == 0) {
+			strcpy(ks_namebuf, name);
+			/* Work out the longest name that matches the prefix */
+			if (++number == 1) {
+				prev_len = min_t(int, max_len-1,
+						 strlen(ks_namebuf));
+				memcpy(ks_namebuf_prev, ks_namebuf, prev_len);
+				ks_namebuf_prev[prev_len] = '\0';
+				continue;
+			}
+			for (i = 0; i < prev_len; i++) {
+				if (ks_namebuf[i] != ks_namebuf_prev[i]) {
+					prev_len = i;
+					ks_namebuf_prev[i] = '\0';
+					break;
+				}
+			}
+		}
+	}
+	if (prev_len > prefix_len)
+		memcpy(prefix_name, ks_namebuf_prev, prev_len+1);
+	return number;
+}
+
+/*
+ * kallsyms_symbol_next
+ *
+ * Parameters:
+ *	prefix_name	prefix of a symbol name to lookup
+ *	flag	0 means search from the head, 1 means continue search.
+ * Returns:
+ *	1 if a symbol matches the given prefix.
+ *	0 if no string found
+ */
+int kallsyms_symbol_next(char *prefix_name, int flag)
+{
+	int prefix_len = strlen(prefix_name);
+	static loff_t pos;
+	const char *name;
+
+	if (!flag)
+		pos = 0;
+
+	while ((name = kdb_walk_kallsyms(&pos))) {
+		if (strncmp(name, prefix_name, prefix_len) == 0) {
+			strncpy(prefix_name, name, strlen(name)+1);
+			return 1;
+		}
+	}
+	return 0;
+}
+
+/*
+ * kdb_symbol_print - Standard method for printing a symbol name and offset.
+ * Inputs:
+ *	addr	Address to be printed.
+ *	symtab	Address of symbol data, if NULL this routine does its
+ *		own lookup.
+ *	punc	Punctuation for string, bit field.
+ * Remarks:
+ *	The string and its punctuation is only printed if the address
+ *	is inside the kernel, except that the value is always printed
+ *	when requested.
+ */
+void kdb_symbol_print(unsigned long addr, const kdb_symtab_t *symtab_p,
+		      unsigned int punc)
+{
+	kdb_symtab_t symtab, *symtab_p2;
+	if (symtab_p) {
+		symtab_p2 = (kdb_symtab_t *)symtab_p;
+	} else {
+		symtab_p2 = &symtab;
+		kdbnearsym(addr, symtab_p2);
+	}
+	if (!(symtab_p2->sym_name || (punc & KDB_SP_VALUE)))
+		return;
+	if (punc & KDB_SP_SPACEB)
+		kdb_printf(" ");
+	if (punc & KDB_SP_VALUE)
+		kdb_printf(kdb_machreg_fmt0, addr);
+	if (symtab_p2->sym_name) {
+		if (punc & KDB_SP_VALUE)
+			kdb_printf(" ");
+		if (punc & KDB_SP_PAREN)
+			kdb_printf("(");
+		if (strcmp(symtab_p2->mod_name, "kernel"))
+			kdb_printf("[%s]", symtab_p2->mod_name);
+		kdb_printf("%s", symtab_p2->sym_name);
+		if (addr != symtab_p2->sym_start)
+			kdb_printf("+0x%lx", addr - symtab_p2->sym_start);
+		if (punc & KDB_SP_SYMSIZE)
+			kdb_printf("/0x%lx",
+				   symtab_p2->sym_end - symtab_p2->sym_start);
+		if (punc & KDB_SP_PAREN)
+			kdb_printf(")");
+	}
+	if (punc & KDB_SP_SPACEA)
+		kdb_printf(" ");
+	if (punc & KDB_SP_NEWLINE)
+		kdb_printf("\n");
+}
+
+/*
+ * kdb_strdup - kdb equivalent of strdup, for disasm code.
+ * Inputs:
+ *	str	The string to duplicate.
+ *	type	Flags to kmalloc for the new string.
+ * Returns:
+ *	Address of the new string, NULL if storage could not be allocated.
+ * Remarks:
+ *	This is not in lib/string.c because it uses kmalloc which is not
+ *	available when string.o is used in boot loaders.
+ */
+char *kdb_strdup(const char *str, gfp_t type)
+{
+	int n = strlen(str)+1;
+	char *s = kmalloc(n, type);
+	if (!s)
+		return NULL;
+	return strcpy(s, str);
+}
+
+/*
+ * kdb_getarea_size - Read an area of data.  The kdb equivalent of
+ *	copy_from_user, with kdb messages for invalid addresses.
+ * Inputs:
+ *	res	Pointer to the area to receive the result.
+ *	addr	Address of the area to copy.
+ *	size	Size of the area.
+ * Returns:
+ *	0 for success, < 0 for error.
+ */
+int kdb_getarea_size(void *res, unsigned long addr, size_t size)
+{
+	int ret = probe_kernel_read((char *)res, (char *)addr, size);
+	if (ret) {
+		if (!KDB_STATE(SUPPRESS)) {
+			kdb_printf("kdb_getarea: Bad address 0x%lx\n", addr);
+			KDB_STATE_SET(SUPPRESS);
+		}
+		ret = KDB_BADADDR;
+	} else {
+		KDB_STATE_CLEAR(SUPPRESS);
+	}
+	return ret;
+}
+
+/*
+ * kdb_putarea_size - Write an area of data.  The kdb equivalent of
+ *	copy_to_user, with kdb messages for invalid addresses.
+ * Inputs:
+ *	addr	Address of the area to write to.
+ *	res	Pointer to the area holding the data.
+ *	size	Size of the area.
+ * Returns:
+ *	0 for success, < 0 for error.
+ */
+int kdb_putarea_size(unsigned long addr, void *res, size_t size)
+{
+	int ret = probe_kernel_read((char *)addr, (char *)res, size);
+	if (ret) {
+		if (!KDB_STATE(SUPPRESS)) {
+			kdb_printf("kdb_putarea: Bad address 0x%lx\n", addr);
+			KDB_STATE_SET(SUPPRESS);
+		}
+		ret = KDB_BADADDR;
+	} else {
+		KDB_STATE_CLEAR(SUPPRESS);
+	}
+	return ret;
+}
+
+/*
+ * kdb_getphys - Read data from a physical address. Validate the
+ * 	address is in range, use kmap_atomic() to get data
+ * 	similar to kdb_getarea() - but for phys addresses
+ * Inputs:
+ * 	res	Pointer to the word to receive the result
+ * 	addr	Physical address of the area to copy
+ * 	size	Size of the area
+ * Returns:
+ *	0 for success, < 0 for error.
+ */
+static int kdb_getphys(void *res, unsigned long addr, size_t size)
+{
+	unsigned long pfn;
+	void *vaddr;
+	struct page *page;
+
+	pfn = (addr >> PAGE_SHIFT);
+	if (!pfn_valid(pfn))
+		return 1;
+	page = pfn_to_page(pfn);
+	vaddr = kmap_atomic(page, KM_KDB);
+	memcpy(res, vaddr + (addr & (PAGE_SIZE - 1)), size);
+	kunmap_atomic(vaddr, KM_KDB);
+
+	return 0;
+}
+
+/*
+ * kdb_getphysword
+ * Inputs:
+ *	word	Pointer to the word to receive the result.
+ *	addr	Address of the area to copy.
+ *	size	Size of the area.
+ * Returns:
+ *	0 for success, < 0 for error.
+ */
+int kdb_getphysword(unsigned long *word, unsigned long addr, size_t size)
+{
+	int diag;
+	__u8  w1;
+	__u16 w2;
+	__u32 w4;
+	__u64 w8;
+	*word = 0;	/* Default value if addr or size is invalid */
+
+	switch (size) {
+	case 1:
+		diag = kdb_getphys(&w1, addr, sizeof(w1));
+		if (!diag)
+			*word = w1;
+		break;
+	case 2:
+		diag = kdb_getphys(&w2, addr, sizeof(w2));
+		if (!diag)
+			*word = w2;
+		break;
+	case 4:
+		diag = kdb_getphys(&w4, addr, sizeof(w4));
+		if (!diag)
+			*word = w4;
+		break;
+	case 8:
+		if (size <= sizeof(*word)) {
+			diag = kdb_getphys(&w8, addr, sizeof(w8));
+			if (!diag)
+				*word = w8;
+			break;
+		}
+		/* drop through */
+	default:
+		diag = KDB_BADWIDTH;
+		kdb_printf("kdb_getphysword: bad width %ld\n", (long) size);
+	}
+	return diag;
+}
+
+/*
+ * kdb_getword - Read a binary value.  Unlike kdb_getarea, this treats
+ *	data as numbers.
+ * Inputs:
+ *	word	Pointer to the word to receive the result.
+ *	addr	Address of the area to copy.
+ *	size	Size of the area.
+ * Returns:
+ *	0 for success, < 0 for error.
+ */
+int kdb_getword(unsigned long *word, unsigned long addr, size_t size)
+{
+	int diag;
+	__u8  w1;
+	__u16 w2;
+	__u32 w4;
+	__u64 w8;
+	*word = 0;	/* Default value if addr or size is invalid */
+	switch (size) {
+	case 1:
+		diag = kdb_getarea(w1, addr);
+		if (!diag)
+			*word = w1;
+		break;
+	case 2:
+		diag = kdb_getarea(w2, addr);
+		if (!diag)
+			*word = w2;
+		break;
+	case 4:
+		diag = kdb_getarea(w4, addr);
+		if (!diag)
+			*word = w4;
+		break;
+	case 8:
+		if (size <= sizeof(*word)) {
+			diag = kdb_getarea(w8, addr);
+			if (!diag)
+				*word = w8;
+			break;
+		}
+		/* drop through */
+	default:
+		diag = KDB_BADWIDTH;
+		kdb_printf("kdb_getword: bad width %ld\n", (long) size);
+	}
+	return diag;
+}
+
+/*
+ * kdb_putword - Write a binary value.  Unlike kdb_putarea, this
+ *	treats data as numbers.
+ * Inputs:
+ *	addr	Address of the area to write to..
+ *	word	The value to set.
+ *	size	Size of the area.
+ * Returns:
+ *	0 for success, < 0 for error.
+ */
+int kdb_putword(unsigned long addr, unsigned long word, size_t size)
+{
+	int diag;
+	__u8  w1;
+	__u16 w2;
+	__u32 w4;
+	__u64 w8;
+	switch (size) {
+	case 1:
+		w1 = word;
+		diag = kdb_putarea(addr, w1);
+		break;
+	case 2:
+		w2 = word;
+		diag = kdb_putarea(addr, w2);
+		break;
+	case 4:
+		w4 = word;
+		diag = kdb_putarea(addr, w4);
+		break;
+	case 8:
+		if (size <= sizeof(word)) {
+			w8 = word;
+			diag = kdb_putarea(addr, w8);
+			break;
+		}
+		/* drop through */
+	default:
+		diag = KDB_BADWIDTH;
+		kdb_printf("kdb_putword: bad width %ld\n", (long) size);
+	}
+	return diag;
+}
+
+/*
+ * kdb_task_state_string - Convert a string containing any of the
+ *	letters DRSTCZEUIMA to a mask for the process state field and
+ *	return the value.  If no argument is supplied, return the mask
+ *	that corresponds to environment variable PS, DRSTCZEU by
+ *	default.
+ * Inputs:
+ *	s	String to convert
+ * Returns:
+ *	Mask for process state.
+ * Notes:
+ *	The mask folds data from several sources into a single long value, so
+ *	be carefull not to overlap the bits.  TASK_* bits are in the LSB,
+ *	special cases like UNRUNNABLE are in the MSB.  As of 2.6.10-rc1 there
+ *	is no overlap between TASK_* and EXIT_* but that may not always be
+ *	true, so EXIT_* bits are shifted left 16 bits before being stored in
+ *	the mask.
+ */
+
+/* unrunnable is < 0 */
+#define UNRUNNABLE	(1UL << (8*sizeof(unsigned long) - 1))
+#define RUNNING		(1UL << (8*sizeof(unsigned long) - 2))
+#define IDLE		(1UL << (8*sizeof(unsigned long) - 3))
+#define DAEMON		(1UL << (8*sizeof(unsigned long) - 4))
+
+unsigned long kdb_task_state_string(const char *s)
+{
+	long res = 0;
+	if (!s) {
+		s = kdbgetenv("PS");
+		if (!s)
+			s = "DRSTCZEU";	/* default value for ps */
+	}
+	while (*s) {
+		switch (*s) {
+		case 'D':
+			res |= TASK_UNINTERRUPTIBLE;
+			break;
+		case 'R':
+			res |= RUNNING;
+			break;
+		case 'S':
+			res |= TASK_INTERRUPTIBLE;
+			break;
+		case 'T':
+			res |= TASK_STOPPED;
+			break;
+		case 'C':
+			res |= TASK_TRACED;
+			break;
+		case 'Z':
+			res |= EXIT_ZOMBIE << 16;
+			break;
+		case 'E':
+			res |= EXIT_DEAD << 16;
+			break;
+		case 'U':
+			res |= UNRUNNABLE;
+			break;
+		case 'I':
+			res |= IDLE;
+			break;
+		case 'M':
+			res |= DAEMON;
+			break;
+		case 'A':
+			res = ~0UL;
+			break;
+		default:
+			  kdb_printf("%s: unknown flag '%c' ignored\n",
+				     __func__, *s);
+			  break;
+		}
+		++s;
+	}
+	return res;
+}
+
+/*
+ * kdb_task_state_char - Return the character that represents the task state.
+ * Inputs:
+ *	p	struct task for the process
+ * Returns:
+ *	One character to represent the task state.
+ */
+char kdb_task_state_char (const struct task_struct *p)
+{
+	int cpu;
+	char state;
+	unsigned long tmp;
+
+	if (!p || probe_kernel_read(&tmp, (char *)p, sizeof(unsigned long)))
+		return 'E';
+
+	cpu = kdb_process_cpu(p);
+	state = (p->state == 0) ? 'R' :
+		(p->state < 0) ? 'U' :
+		(p->state & TASK_UNINTERRUPTIBLE) ? 'D' :
+		(p->state & TASK_STOPPED) ? 'T' :
+		(p->state & TASK_TRACED) ? 'C' :
+		(p->exit_state & EXIT_ZOMBIE) ? 'Z' :
+		(p->exit_state & EXIT_DEAD) ? 'E' :
+		(p->state & TASK_INTERRUPTIBLE) ? 'S' : '?';
+	if (p->pid == 0) {
+		/* Idle task.  Is it really idle, apart from the kdb
+		 * interrupt? */
+		if (!kdb_task_has_cpu(p) || kgdb_info[cpu].irq_depth == 1) {
+			if (cpu != kdb_initial_cpu)
+				state = 'I';	/* idle task */
+		}
+	} else if (!p->mm && state == 'S') {
+		state = 'M';	/* sleeping system daemon */
+	}
+	return state;
+}
+
+/*
+ * kdb_task_state - Return true if a process has the desired state
+ *	given by the mask.
+ * Inputs:
+ *	p	struct task for the process
+ *	mask	mask from kdb_task_state_string to select processes
+ * Returns:
+ *	True if the process matches at least one criteria defined by the mask.
+ */
+unsigned long kdb_task_state(const struct task_struct *p, unsigned long mask)
+{
+	char state[] = { kdb_task_state_char(p), '\0' };
+	return (mask & kdb_task_state_string(state)) != 0;
+}
+
+/*
+ * kdb_print_nameval - Print a name and its value, converting the
+ *	value to a symbol lookup if possible.
+ * Inputs:
+ *	name	field name to print
+ *	val	value of field
+ */
+void kdb_print_nameval(const char *name, unsigned long val)
+{
+	kdb_symtab_t symtab;
+	kdb_printf("  %-11.11s ", name);
+	if (kdbnearsym(val, &symtab))
+		kdb_symbol_print(val, &symtab,
+				 KDB_SP_VALUE|KDB_SP_SYMSIZE|KDB_SP_NEWLINE);
+	else
+		kdb_printf("0x%lx\n", val);
+}
+
+/* Last ditch allocator for debugging, so we can still debug even when
+ * the GFP_ATOMIC pool has been exhausted.  The algorithms are tuned
+ * for space usage, not for speed.  One smallish memory pool, the free
+ * chain is always in ascending address order to allow coalescing,
+ * allocations are done in brute force best fit.
+ */
+
+struct debug_alloc_header {
+	u32 next;	/* offset of next header from start of pool */
+	u32 size;
+	void *caller;
+};
+
+/* The memory returned by this allocator must be aligned, which means
+ * so must the header size.  Do not assume that sizeof(struct
+ * debug_alloc_header) is a multiple of the alignment, explicitly
+ * calculate the overhead of this header, including the alignment.
+ * The rest of this code must not use sizeof() on any header or
+ * pointer to a header.
+ */
+#define dah_align 8
+#define dah_overhead ALIGN(sizeof(struct debug_alloc_header), dah_align)
+
+static u64 debug_alloc_pool_aligned[256*1024/dah_align];	/* 256K pool */
+static char *debug_alloc_pool = (char *)debug_alloc_pool_aligned;
+static u32 dah_first, dah_first_call = 1, dah_used, dah_used_max;
+
+/* Locking is awkward.  The debug code is called from all contexts,
+ * including non maskable interrupts.  A normal spinlock is not safe
+ * in NMI context.  Try to get the debug allocator lock, if it cannot
+ * be obtained after a second then give up.  If the lock could not be
+ * previously obtained on this cpu then only try once.
+ *
+ * sparse has no annotation for "this function _sometimes_ acquires a
+ * lock", so fudge the acquire/release notation.
+ */
+static DEFINE_SPINLOCK(dap_lock);
+static int get_dap_lock(void)
+	__acquires(dap_lock)
+{
+	static int dap_locked = -1;
+	int count;
+	if (dap_locked == smp_processor_id())
+		count = 1;
+	else
+		count = 1000;
+	while (1) {
+		if (spin_trylock(&dap_lock)) {
+			dap_locked = -1;
+			return 1;
+		}
+		if (!count--)
+			break;
+		udelay(1000);
+	}
+	dap_locked = smp_processor_id();
+	__acquire(dap_lock);
+	return 0;
+}
+
+void *debug_kmalloc(size_t size, gfp_t flags)
+{
+	unsigned int rem, h_offset;
+	struct debug_alloc_header *best, *bestprev, *prev, *h;
+	void *p = NULL;
+	if (!get_dap_lock()) {
+		__release(dap_lock);	/* we never actually got it */
+		return NULL;
+	}
+	h = (struct debug_alloc_header *)(debug_alloc_pool + dah_first);
+	if (dah_first_call) {
+		h->size = sizeof(debug_alloc_pool_aligned) - dah_overhead;
+		dah_first_call = 0;
+	}
+	size = ALIGN(size, dah_align);
+	prev = best = bestprev = NULL;
+	while (1) {
+		if (h->size >= size && (!best || h->size < best->size)) {
+			best = h;
+			bestprev = prev;
+			if (h->size == size)
+				break;
+		}
+		if (!h->next)
+			break;
+		prev = h;
+		h = (struct debug_alloc_header *)(debug_alloc_pool + h->next);
+	}
+	if (!best)
+		goto out;
+	rem = best->size - size;
+	/* The pool must always contain at least one header */
+	if (best->next == 0 && bestprev == NULL && rem < dah_overhead)
+		goto out;
+	if (rem >= dah_overhead) {
+		best->size = size;
+		h_offset = ((char *)best - debug_alloc_pool) +
+			   dah_overhead + best->size;
+		h = (struct debug_alloc_header *)(debug_alloc_pool + h_offset);
+		h->size = rem - dah_overhead;
+		h->next = best->next;
+	} else
+		h_offset = best->next;
+	best->caller = __builtin_return_address(0);
+	dah_used += best->size;
+	dah_used_max = max(dah_used, dah_used_max);
+	if (bestprev)
+		bestprev->next = h_offset;
+	else
+		dah_first = h_offset;
+	p = (char *)best + dah_overhead;
+	memset(p, POISON_INUSE, best->size - 1);
+	*((char *)p + best->size - 1) = POISON_END;
+out:
+	spin_unlock(&dap_lock);
+	return p;
+}
+
+void debug_kfree(void *p)
+{
+	struct debug_alloc_header *h;
+	unsigned int h_offset;
+	if (!p)
+		return;
+	if ((char *)p < debug_alloc_pool ||
+	    (char *)p >= debug_alloc_pool + sizeof(debug_alloc_pool_aligned)) {
+		kfree(p);
+		return;
+	}
+	if (!get_dap_lock()) {
+		__release(dap_lock);	/* we never actually got it */
+		return;		/* memory leak, cannot be helped */
+	}
+	h = (struct debug_alloc_header *)((char *)p - dah_overhead);
+	memset(p, POISON_FREE, h->size - 1);
+	*((char *)p + h->size - 1) = POISON_END;
+	h->caller = NULL;
+	dah_used -= h->size;
+	h_offset = (char *)h - debug_alloc_pool;
+	if (h_offset < dah_first) {
+		h->next = dah_first;
+		dah_first = h_offset;
+	} else {
+		struct debug_alloc_header *prev;
+		unsigned int prev_offset;
+		prev = (struct debug_alloc_header *)(debug_alloc_pool +
+						     dah_first);
+		while (1) {
+			if (!prev->next || prev->next > h_offset)
+				break;
+			prev = (struct debug_alloc_header *)
+				(debug_alloc_pool + prev->next);
+		}
+		prev_offset = (char *)prev - debug_alloc_pool;
+		if (prev_offset + dah_overhead + prev->size == h_offset) {
+			prev->size += dah_overhead + h->size;
+			memset(h, POISON_FREE, dah_overhead - 1);
+			*((char *)h + dah_overhead - 1) = POISON_END;
+			h = prev;
+			h_offset = prev_offset;
+		} else {
+			h->next = prev->next;
+			prev->next = h_offset;
+		}
+	}
+	if (h_offset + dah_overhead + h->size == h->next) {
+		struct debug_alloc_header *next;
+		next = (struct debug_alloc_header *)
+			(debug_alloc_pool + h->next);
+		h->size += dah_overhead + next->size;
+		h->next = next->next;
+		memset(next, POISON_FREE, dah_overhead - 1);
+		*((char *)next + dah_overhead - 1) = POISON_END;
+	}
+	spin_unlock(&dap_lock);
+}
+
+void debug_kusage(void)
+{
+	struct debug_alloc_header *h_free, *h_used;
+#ifdef	CONFIG_IA64
+	/* FIXME: using dah for ia64 unwind always results in a memory leak.
+	 * Fix that memory leak first, then set debug_kusage_one_time = 1 for
+	 * all architectures.
+	 */
+	static int debug_kusage_one_time;
+#else
+	static int debug_kusage_one_time = 1;
+#endif
+	if (!get_dap_lock()) {
+		__release(dap_lock);	/* we never actually got it */
+		return;
+	}
+	h_free = (struct debug_alloc_header *)(debug_alloc_pool + dah_first);
+	if (dah_first == 0 &&
+	    (h_free->size == sizeof(debug_alloc_pool_aligned) - dah_overhead ||
+	     dah_first_call))
+		goto out;
+	if (!debug_kusage_one_time)
+		goto out;
+	debug_kusage_one_time = 0;
+	kdb_printf("%s: debug_kmalloc memory leak dah_first %d\n",
+		   __func__, dah_first);
+	if (dah_first) {
+		h_used = (struct debug_alloc_header *)debug_alloc_pool;
+		kdb_printf("%s: h_used %p size %d\n", __func__, h_used,
+			   h_used->size);
+	}
+	do {
+		h_used = (struct debug_alloc_header *)
+			  ((char *)h_free + dah_overhead + h_free->size);
+		kdb_printf("%s: h_used %p size %d caller %p\n",
+			   __func__, h_used, h_used->size, h_used->caller);
+		h_free = (struct debug_alloc_header *)
+			  (debug_alloc_pool + h_free->next);
+	} while (h_free->next);
+	h_used = (struct debug_alloc_header *)
+		  ((char *)h_free + dah_overhead + h_free->size);
+	if ((char *)h_used - debug_alloc_pool !=
+	    sizeof(debug_alloc_pool_aligned))
+		kdb_printf("%s: h_used %p size %d caller %p\n",
+			   __func__, h_used, h_used->size, h_used->caller);
+out:
+	spin_unlock(&dap_lock);
+}
+
+/* Maintain a small stack of kdb_flags to allow recursion without disturbing
+ * the global kdb state.
+ */
+
+static int kdb_flags_stack[4], kdb_flags_index;
+
+void kdb_save_flags(void)
+{
+	BUG_ON(kdb_flags_index >= ARRAY_SIZE(kdb_flags_stack));
+	kdb_flags_stack[kdb_flags_index++] = kdb_flags;
+}
+
+void kdb_restore_flags(void)
+{
+	BUG_ON(kdb_flags_index <= 0);
+	kdb_flags = kdb_flags_stack[--kdb_flags_index];
+}