kdb_support.c

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/*
 * 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 <[email protected]>
 */

#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 = 0;
    unsigned long offset = 0;
#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);
    memcpy(res, vaddr + (addr & (PAGE_SIZE - 1)), size);
    kunmap_atomic(vaddr);

    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 careful 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 (is_idle_task(p)) {
        /* 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];
}