malloc.c

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#define _GNU_SOURCE
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <stdint.h>
#include <errno.h>
#include <sys/mman.h>
#include "libc.h"
#include "atomic.h"
#include "pthread_impl.h"
 
#if defined(__GNUC__) && defined(__PIC__)
#define inline inline __attribute__((always_inline))
#endif
 
void *__mmap(void *, size_t, int, int, int, off_t);
int __munmap(void *, size_t);
void *__mremap(void *, size_t, size_t, int, ...);
int __madvise(void *, size_t, int);
 
struct chunk {
    size_t psize, csize;
    struct chunk *next, *prev;
};
 
struct bin {
    volatile int lock[2];
    struct chunk *head;
    struct chunk *tail;
};
 
static struct {
    volatile uint64_t binmap;
    struct bin bins[64];
    volatile int free_lock[2];
} mal;
 
 
#define SIZE_ALIGN (4*sizeof(size_t))
#define SIZE_MASK (-SIZE_ALIGN)
#define OVERHEAD (2*sizeof(size_t))
#define MMAP_THRESHOLD (0x1c00*SIZE_ALIGN)
#define DONTCARE 16
#define RECLAIM 163840
 
#define CHUNK_SIZE(c) ((c)->csize & -2)
#define CHUNK_PSIZE(c) ((c)->psize & -2)
#define PREV_CHUNK(c) ((struct chunk *)((char *)(c) - CHUNK_PSIZE(c)))
#define NEXT_CHUNK(c) ((struct chunk *)((char *)(c) + CHUNK_SIZE(c)))
#define MEM_TO_CHUNK(p) (struct chunk *)((char *)(p) - OVERHEAD)
#define CHUNK_TO_MEM(c) (void *)((char *)(c) + OVERHEAD)
#define BIN_TO_CHUNK(i) (MEM_TO_CHUNK(&mal.bins[i].head))
 
#define C_INUSE  ((size_t)1)
 
#define IS_MMAPPED(c) !((c)->csize & (C_INUSE))
 
 
/* Synchronization tools */
 
static inline void lock(volatile int *lk)
{
    if (libc.threads_minus_1)
        while(a_swap(lk, 1)) __wait(lk, lk+1, 1, 1);
}
 
static inline void unlock(volatile int *lk)
{
    if (lk[0]) {
        a_store(lk, 0);
        if (lk[1]) __wake(lk, 1, 1);
    }
}
 
static inline void lock_bin(int i)
{
    lock(mal.bins[i].lock);
    if (!mal.bins[i].head)
        mal.bins[i].head = mal.bins[i].tail = BIN_TO_CHUNK(i);
}
 
static inline void unlock_bin(int i)
{
    unlock(mal.bins[i].lock);
}
 
static int first_set(uint64_t x)
{
#if 1
    return a_ctz_64(x);
#else
    static const char debruijn64[64] = {
        0, 1, 2, 53, 3, 7, 54, 27, 4, 38, 41, 8, 34, 55, 48, 28,
        62, 5, 39, 46, 44, 42, 22, 9, 24, 35, 59, 56, 49, 18, 29, 11,
        63, 52, 6, 26, 37, 40, 33, 47, 61, 45, 43, 21, 23, 58, 17, 10,
        51, 25, 36, 32, 60, 20, 57, 16, 50, 31, 19, 15, 30, 14, 13, 12
    };
    static const char debruijn32[32] = {
        0, 1, 23, 2, 29, 24, 19, 3, 30, 27, 25, 11, 20, 8, 4, 13,
        31, 22, 28, 18, 26, 10, 7, 12, 21, 17, 9, 6, 16, 5, 15, 14
    };
    if (sizeof(long) < 8) {
        uint32_t y = x;
        if (!y) {
            y = x>>32;
            return 32 + debruijn32[(y&-y)*0x076be629 >> 27];
        }
        return debruijn32[(y&-y)*0x076be629 >> 27];
    }
    return debruijn64[(x&-x)*0x022fdd63cc95386dull >> 58];
#endif
}
 
static const unsigned char bin_tab[60] = {
                32,33,34,35,36,36,37,37,38,38,39,39,
    40,40,40,40,41,41,41,41,42,42,42,42,43,43,43,43,
    44,44,44,44,44,44,44,44,45,45,45,45,45,45,45,45,
    46,46,46,46,46,46,46,46,47,47,47,47,47,47,47,47,
};
 
static int bin_index(size_t x)
{
    x = x / SIZE_ALIGN - 1;
    if (x <= 32) return x;
    if (x < 512) return bin_tab[x/8-4];
    if (x > 0x1c00) return 63;
    return bin_tab[x/128-4] + 16;
}
 
static int bin_index_up(size_t x)
{
    x = x / SIZE_ALIGN - 1;
    if (x <= 32) return x;
    x--;
    if (x < 512) return bin_tab[x/8-4] + 1;
    return bin_tab[x/128-4] + 17;
}
 
#if 0
void __dump_heap(int x)
{
    struct chunk *c;
    int i;
    for (c = (void *)mal.heap; CHUNK_SIZE(c); c = NEXT_CHUNK(c))
        fprintf(stderr, "base %p size %zu (%d) flags %d/%d\n",
            c, CHUNK_SIZE(c), bin_index(CHUNK_SIZE(c)),
            c->csize & 15,
            NEXT_CHUNK(c)->psize & 15);
    for (i=0; i<64; i++) {
        if (mal.bins[i].head != BIN_TO_CHUNK(i) && mal.bins[i].head) {
            fprintf(stderr, "bin %d: %p\n", i, mal.bins[i].head);
            if (!(mal.binmap & 1ULL<<i))
                fprintf(stderr, "missing from binmap!\n");
        } else if (mal.binmap & 1ULL<<i)
            fprintf(stderr, "binmap wrongly contains %d!\n", i);
    }
}
#endif
 
void *__expand_heap(size_t *);
 
static struct chunk *expand_heap(size_t n)
{
    static int heap_lock[2];
    static void *end;
    void *p;
    struct chunk *w;
 
    /* The argument n already accounts for the caller's chunk
     * overhead needs, but if the heap can't be extended in-place,
     * we need room for an extra zero-sized sentinel chunk. */
    n += SIZE_ALIGN;
 
    lock(heap_lock);
 
    p = __expand_heap(&n);
    if (!p) {
        unlock(heap_lock);
        return 0;
    }
 
    /* If not just expanding existing space, we need to make a
     * new sentinel chunk below the allocated space. */
    if (p != end) {
        /* Valid/safe because of the prologue increment. */
        n -= SIZE_ALIGN;
        p = (char *)p + SIZE_ALIGN;
        w = MEM_TO_CHUNK(p);
        w->psize = 0 | C_INUSE;
    }
 
    /* Record new heap end and fill in footer. */
    end = (char *)p + n;
    w = MEM_TO_CHUNK(end);
    w->psize = n | C_INUSE;
    w->csize = 0 | C_INUSE;
 
    /* Fill in header, which may be new or may be replacing a
     * zero-size sentinel header at the old end-of-heap. */
    w = MEM_TO_CHUNK(p);
    w->csize = n | C_INUSE;
 
    unlock(heap_lock);
 
    return w;
}
 
static int adjust_size(size_t *n)
{
    /* Result of pointer difference must fit in ptrdiff_t. */
    if (*n-1 > PTRDIFF_MAX - SIZE_ALIGN - PAGE_SIZE) {
        if (*n) {
            errno = ENOMEM;
            return -1;
        } else {
            *n = SIZE_ALIGN;
            return 0;
        }
    }
    *n = (*n + OVERHEAD + SIZE_ALIGN - 1) & SIZE_MASK;
    return 0;
}
 
static void unbin(struct chunk *c, int i)
{
    if (c->prev == c->next)
        a_and_64(&mal.binmap, ~(1ULL<<i));
    c->prev->next = c->next;
    c->next->prev = c->prev;
    c->csize |= C_INUSE;
    NEXT_CHUNK(c)->psize |= C_INUSE;
}
 
static int alloc_fwd(struct chunk *c)
{
    int i;
    size_t k;
    while (!((k=c->csize) & C_INUSE)) {
        i = bin_index(k);
        lock_bin(i);
        if (c->csize == k) {
            unbin(c, i);
            unlock_bin(i);
            return 1;
        }
        unlock_bin(i);
    }
    return 0;
}
 
static int alloc_rev(struct chunk *c)
{
    int i;
    size_t k;
    while (!((k=c->psize) & C_INUSE)) {
        i = bin_index(k);
        lock_bin(i);
        if (c->psize == k) {
            unbin(PREV_CHUNK(c), i);
            unlock_bin(i);
            return 1;
        }
        unlock_bin(i);
    }
    return 0;
}
 
 
/* pretrim - trims a chunk _prior_ to removing it from its bin.
 * Must be called with i as the ideal bin for size n, j the bin
 * for the _free_ chunk self, and bin j locked. */
static int pretrim(struct chunk *self, size_t n, int i, int j)
{
    size_t n1;
    struct chunk *next, *split;
 
    /* We cannot pretrim if it would require re-binning. */
    if (j < 40) return 0;
    if (j < i+3) {
        if (j != 63) return 0;
        n1 = CHUNK_SIZE(self);
        if (n1-n <= MMAP_THRESHOLD) return 0;
    } else {
        n1 = CHUNK_SIZE(self);
    }
    if (bin_index(n1-n) != j) return 0;
 
    next = NEXT_CHUNK(self);
    split = (void *)((char *)self + n);
 
    split->prev = self->prev;
    split->next = self->next;
    split->prev->next = split;
    split->next->prev = split;
    split->psize = n | C_INUSE;
    split->csize = n1-n;
    next->psize = n1-n;
    self->csize = n | C_INUSE;
    return 1;
}
 
static void trim(struct chunk *self, size_t n)
{
    size_t n1 = CHUNK_SIZE(self);
    struct chunk *next, *split;
 
    if (n >= n1 - DONTCARE) return;
 
    next = NEXT_CHUNK(self);
    split = (void *)((char *)self + n);
 
    split->psize = n | C_INUSE;
    split->csize = n1-n | C_INUSE;
    next->psize = n1-n | C_INUSE;
    self->csize = n | C_INUSE;
 
    free(CHUNK_TO_MEM(split));
}
 
void *malloc(size_t n)
{
    struct chunk *c;
    int i, j;
 
    if (adjust_size(&n) < 0) return 0;
 
    if (n > MMAP_THRESHOLD) {
        size_t len = n + OVERHEAD + PAGE_SIZE - 1 & -PAGE_SIZE;
        char *base = __mmap(0, len, PROT_READ|PROT_WRITE,
            MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
        if (base == (void *)-1) return 0;
        c = (void *)(base + SIZE_ALIGN - OVERHEAD);
        c->csize = len - (SIZE_ALIGN - OVERHEAD);
        c->psize = SIZE_ALIGN - OVERHEAD;
        return CHUNK_TO_MEM(c);
    }
 
    i = bin_index_up(n);
    for (;;) {
        uint64_t mask = mal.binmap & -(1ULL<<i);
        if (!mask) {
            c = expand_heap(n);
            if (!c) return 0;
            if (alloc_rev(c)) {
                struct chunk *x = c;
                c = PREV_CHUNK(c);
                NEXT_CHUNK(x)->psize = c->csize =
                    x->csize + CHUNK_SIZE(c);
            }
            break;
        }
        j = first_set(mask);
        lock_bin(j);
        c = mal.bins[j].head;
        if (c != BIN_TO_CHUNK(j)) {
            if (!pretrim(c, n, i, j)) unbin(c, j);
            unlock_bin(j);
            break;
        }
        unlock_bin(j);
    }
 
    /* Now patch up in case we over-allocated */
    trim(c, n);
 
    return CHUNK_TO_MEM(c);
}
 
void *__malloc0(size_t n)
{
    void *p = malloc(n);
    if (p && !IS_MMAPPED(MEM_TO_CHUNK(p))) {
        size_t *z;
        n = (n + sizeof *z - 1)/sizeof *z;
        for (z=p; n; n--, z++) if (*z) *z=0;
    }
    return p;
}
 
void *realloc(void *p, size_t n)
{
    struct chunk *self, *next;
    size_t n0, n1;
    void *new;
 
    if (!p) return malloc(n);
 
    if (adjust_size(&n) < 0) return 0;
 
    self = MEM_TO_CHUNK(p);
    n1 = n0 = CHUNK_SIZE(self);
 
    if (IS_MMAPPED(self)) {
        size_t extra = self->psize;
        char *base = (char *)self - extra;
        size_t oldlen = n0 + extra;
        size_t newlen = n + extra;
        /* Crash on realloc of freed chunk */
        if (extra & 1) a_crash();
        if (newlen < PAGE_SIZE && (new = malloc(n))) {
            memcpy(new, p, n-OVERHEAD);
            free(p);
            return new;
        }
        newlen = (newlen + PAGE_SIZE-1) & -PAGE_SIZE;
        if (oldlen == newlen) return p;
        base = __mremap(base, oldlen, newlen, MREMAP_MAYMOVE);
        if (base == (void *)-1)
            goto copy_realloc;
        self = (void *)(base + extra);
        self->csize = newlen - extra;
        return CHUNK_TO_MEM(self);
    }
 
    next = NEXT_CHUNK(self);
 
    /* Crash on corrupted footer (likely from buffer overflow) */
    if (next->psize != self->csize) a_crash();
 
    /* Merge adjacent chunks if we need more space. This is not
     * a waste of time even if we fail to get enough space, because our
     * subsequent call to free would otherwise have to do the merge. */
    if (n > n1 && alloc_fwd(next)) {
        n1 += CHUNK_SIZE(next);
        next = NEXT_CHUNK(next);
    }
    /* FIXME: find what's wrong here and reenable it..? */
    if (0 && n > n1 && alloc_rev(self)) {
        self = PREV_CHUNK(self);
        n1 += CHUNK_SIZE(self);
    }
    self->csize = n1 | C_INUSE;
    next->psize = n1 | C_INUSE;
 
    /* If we got enough space, split off the excess and return */
    if (n <= n1) {
        //memmove(CHUNK_TO_MEM(self), p, n0-OVERHEAD);
        trim(self, n);
        return CHUNK_TO_MEM(self);
    }
 
copy_realloc:
    /* As a last resort, allocate a new chunk and copy to it. */
    new = malloc(n-OVERHEAD);
    if (!new) return 0;
    memcpy(new, p, n0-OVERHEAD);
    free(CHUNK_TO_MEM(self));
    return new;
}
 
void free(void *p)
{
    struct chunk *self = MEM_TO_CHUNK(p);
    struct chunk *next;
    size_t final_size, new_size, size;
    int reclaim=0;
    int i;
 
    if (!p) return;
 
    if (IS_MMAPPED(self)) {
        size_t extra = self->psize;
        char *base = (char *)self - extra;
        size_t len = CHUNK_SIZE(self) + extra;
        /* Crash on double free */
        if (extra & 1) a_crash();
        __munmap(base, len);
        return;
    }
 
    final_size = new_size = CHUNK_SIZE(self);
    next = NEXT_CHUNK(self);
 
    /* Crash on corrupted footer (likely from buffer overflow) */
    if (next->psize != self->csize) a_crash();
 
    for (;;) {
        if (self->psize & next->csize & C_INUSE) {
            self->csize = final_size | C_INUSE;
            next->psize = final_size | C_INUSE;
            i = bin_index(final_size);
            lock_bin(i);
            lock(mal.free_lock);
            if (self->psize & next->csize & C_INUSE)
                break;
            unlock(mal.free_lock);
            unlock_bin(i);
        }
 
        if (alloc_rev(self)) {
            self = PREV_CHUNK(self);
            size = CHUNK_SIZE(self);
            final_size += size;
            if (new_size+size > RECLAIM && (new_size+size^size) > size)
                reclaim = 1;
        }
 
        if (alloc_fwd(next)) {
            size = CHUNK_SIZE(next);
            final_size += size;
            if (new_size+size > RECLAIM && (new_size+size^size) > size)
                reclaim = 1;
            next = NEXT_CHUNK(next);
        }
    }
 
    if (!(mal.binmap & 1ULL<<i))
        a_or_64(&mal.binmap, 1ULL<<i);
 
    self->csize = final_size;
    next->psize = final_size;
    unlock(mal.free_lock);
 
    self->next = BIN_TO_CHUNK(i);
    self->prev = mal.bins[i].tail;
    self->next->prev = self;
    self->prev->next = self;
 
    /* Replace middle of large chunks with fresh zero pages */
    if (reclaim) {
        uintptr_t a = (uintptr_t)self + SIZE_ALIGN+PAGE_SIZE-1 & -PAGE_SIZE;
        uintptr_t b = (uintptr_t)next - SIZE_ALIGN & -PAGE_SIZE;
#if 1
        __madvise((void *)a, b-a, MADV_DONTNEED);
#else
        __mmap((void *)a, b-a, PROT_READ|PROT_WRITE,
            MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0);
#endif
    }
 
    unlock_bin(i);
}