tor

memarea.c (11535B)

---

/* Copyright (c) 2008-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
* \file memarea.c
*
* \brief Implementation for memarea_t, an allocator for allocating lots of
* small objects that will be freed all at once.
*/

#include "orconfig.h"
#include "lib/memarea/memarea.h"

#include <stdlib.h>
#include <string.h>

#include "lib/arch/bytes.h"
#include "lib/cc/torint.h"
#include "lib/smartlist_core/smartlist_core.h"
#include "lib/smartlist_core/smartlist_foreach.h"
#include "lib/log/log.h"
#include "lib/log/util_bug.h"
#include "lib/malloc/malloc.h"

#ifndef DISABLE_MEMORY_SENTINELS

/** If true, we try to detect any attempts to write beyond the length of a
* memarea. */
#define USE_SENTINELS

/** All returned pointers should be aligned to the nearest multiple of this
* value. */
#define MEMAREA_ALIGN SIZEOF_VOID_P

/** A value which, when masked out of a pointer, produces a maximally aligned
* pointer. */
#if MEMAREA_ALIGN == 4
#define MEMAREA_ALIGN_MASK ((uintptr_t)3)
#elif MEMAREA_ALIGN == 8
#define MEMAREA_ALIGN_MASK ((uintptr_t)7)
#else
#error "void* is neither 4 nor 8 bytes long."
#endif /* MEMAREA_ALIGN == 4 || ... */

#if defined(__GNUC__) && defined(FLEXIBLE_ARRAY_MEMBER)
#define USE_ALIGNED_ATTRIBUTE
/** Name for the 'memory' member of a memory chunk. */
#define U_MEM mem
#else
#define U_MEM u.mem
#endif /* defined(__GNUC__) && defined(FLEXIBLE_ARRAY_MEMBER) */

#ifdef USE_SENTINELS
/** Magic value that we stick at the end of a memarea so we can make sure
* there are no run-off-the-end bugs. */
#define SENTINEL_VAL 0x90806622u
/** How many bytes per area do we devote to the sentinel? */
#define SENTINEL_LEN sizeof(uint32_t)
/** Given a mem_area_chunk_t with SENTINEL_LEN extra bytes allocated at the
* end, set those bytes. */
#define SET_SENTINEL(chunk)                                     \
 STMT_BEGIN                                                    \
 set_uint32( &(chunk)->U_MEM[chunk->mem_size], SENTINEL_VAL ); \
 STMT_END
/** Assert that the sentinel on a memarea is set correctly. */
#define CHECK_SENTINEL(chunk)                                           \
 STMT_BEGIN                                                            \
 uint32_t sent_val = get_uint32(&(chunk)->U_MEM[chunk->mem_size]);     \
 tor_assert(sent_val == SENTINEL_VAL);                                 \
 STMT_END
#else /* !defined(USE_SENTINELS) */
#define SENTINEL_LEN 0
#define SET_SENTINEL(chunk) STMT_NIL
#define CHECK_SENTINEL(chunk) STMT_NIL
#endif /* defined(USE_SENTINELS) */

/** Increment <b>ptr</b> until it is aligned to MEMAREA_ALIGN. */
static inline void *
realign_pointer(void *ptr)
{
 uintptr_t x = (uintptr_t)ptr;
 x = (x+MEMAREA_ALIGN_MASK) & ~MEMAREA_ALIGN_MASK;
 /* Reinstate this if bug 930 ever reappears
 tor_assert(((void*)x) >= ptr);
 */
 return (void*)x;
}

/** Implements part of a memarea.  New memory is carved off from chunk->mem in
* increasing order until a request is too big, at which point a new chunk is
* allocated. */
typedef struct memarea_chunk_t {
 /** Next chunk in this area. Only kept around so we can free it. */
 struct memarea_chunk_t *next_chunk;
 size_t mem_size; /**< How much RAM is available in mem, total? */
 char *next_mem; /**< Next position in mem to allocate data at.  If it's
                  * equal to mem+mem_size, this chunk is full. */
#ifdef USE_ALIGNED_ATTRIBUTE
 /** Actual content of the memory chunk. */
 char mem[FLEXIBLE_ARRAY_MEMBER] __attribute__((aligned(MEMAREA_ALIGN)));
#else
 union {
   char mem[1]; /**< Memory space in this chunk.  */
   void *void_for_alignment_; /**< Dummy; used to make sure mem is aligned. */
 } u; /**< Union used to enforce alignment when we don't have support for
       * doing it right. */
#endif /* defined(USE_ALIGNED_ATTRIBUTE) */
} memarea_chunk_t;

/** How many bytes are needed for overhead before we get to the memory part
* of a chunk? */
#define CHUNK_HEADER_SIZE offsetof(memarea_chunk_t, U_MEM)

/** What's the smallest that we'll allocate a chunk? */
#define CHUNK_SIZE 4096

/** A memarea_t is an allocation region for a set of small memory requests
* that will all be freed at once. */
struct memarea_t {
 memarea_chunk_t *first; /**< Top of the chunk stack: never NULL. */
};

/** Helper: allocate a new memarea chunk of around <b>chunk_size</b> bytes. */
static memarea_chunk_t *
alloc_chunk(size_t sz)
{
 tor_assert(sz < SIZE_T_CEILING);

 size_t chunk_size = sz < CHUNK_SIZE ? CHUNK_SIZE : sz;
 memarea_chunk_t *res;
 chunk_size += SENTINEL_LEN;
 res = tor_malloc(chunk_size);
 res->next_chunk = NULL;
 res->mem_size = chunk_size - CHUNK_HEADER_SIZE - SENTINEL_LEN;
 res->next_mem = res->U_MEM;
 tor_assert(res->next_mem+res->mem_size+SENTINEL_LEN ==
            ((char*)res)+chunk_size);
 tor_assert(realign_pointer(res->next_mem) == res->next_mem);
 SET_SENTINEL(res);
 return res;
}

/** Release <b>chunk</b> from a memarea. */
static void
memarea_chunk_free_unchecked(memarea_chunk_t *chunk)
{
 CHECK_SENTINEL(chunk);
 tor_free(chunk);
}

/** Allocate and return new memarea. */
memarea_t *
memarea_new(void)
{
 memarea_t *head = tor_malloc(sizeof(memarea_t));
 head->first = alloc_chunk(CHUNK_SIZE);
 return head;
}

/** Free <b>area</b>, invalidating all pointers returned from memarea_alloc()
* and friends for this area */
void
memarea_drop_all_(memarea_t *area)
{
 memarea_chunk_t *chunk, *next;
 for (chunk = area->first; chunk; chunk = next) {
   next = chunk->next_chunk;
   memarea_chunk_free_unchecked(chunk);
 }
 area->first = NULL; /*fail fast on */
 tor_free(area);
}

/** Forget about having allocated anything in <b>area</b>, and free some of
* the backing storage associated with it, as appropriate. Invalidates all
* pointers returned from memarea_alloc() for this area. */
void
memarea_clear(memarea_t *area)
{
 memarea_chunk_t *chunk, *next;
 if (area->first->next_chunk) {
   for (chunk = area->first->next_chunk; chunk; chunk = next) {
     next = chunk->next_chunk;
     memarea_chunk_free_unchecked(chunk);
   }
   area->first->next_chunk = NULL;
 }
 area->first->next_mem = area->first->U_MEM;
}

/** Return true iff <b>p</b> is in a range that has been returned by an
* allocation from <b>area</b>. */
int
memarea_owns_ptr(const memarea_t *area, const void *p)
{
 memarea_chunk_t *chunk;
 const char *ptr = p;
 for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
   if (ptr >= chunk->U_MEM && ptr < chunk->next_mem)
     return 1;
 }
 return 0;
}

/** Return a pointer to a chunk of memory in <b>area</b> of at least <b>sz</b>
* bytes.  <b>sz</b> should be significantly smaller than the area's chunk
* size, though we can deal if it isn't. */
void *
memarea_alloc(memarea_t *area, size_t sz)
{
 memarea_chunk_t *chunk = area->first;
 char *result;
 tor_assert(chunk);
 CHECK_SENTINEL(chunk);
 tor_assert(sz < SIZE_T_CEILING);
 if (sz == 0)
   sz = 1;
 tor_assert(chunk->next_mem <= chunk->U_MEM + chunk->mem_size);
 const size_t space_remaining =
   (chunk->U_MEM + chunk->mem_size) - chunk->next_mem;
 if (sz > space_remaining) {
   if (sz+CHUNK_HEADER_SIZE >= CHUNK_SIZE) {
     /* This allocation is too big.  Stick it in a special chunk, and put
      * that chunk second in the list. */
     memarea_chunk_t *new_chunk = alloc_chunk(sz+CHUNK_HEADER_SIZE);
     new_chunk->next_chunk = chunk->next_chunk;
     chunk->next_chunk = new_chunk;
     chunk = new_chunk;
   } else {
     memarea_chunk_t *new_chunk = alloc_chunk(CHUNK_SIZE);
     new_chunk->next_chunk = chunk;
     area->first = chunk = new_chunk;
   }
   tor_assert(chunk->mem_size >= sz);
 }
 result = chunk->next_mem;
 chunk->next_mem = chunk->next_mem + sz;
 /* Reinstate these if bug 930 ever comes back
 tor_assert(chunk->next_mem >= chunk->U_MEM);
 tor_assert(chunk->next_mem <= chunk->U_MEM+chunk->mem_size);
 */
 chunk->next_mem = realign_pointer(chunk->next_mem);
 return result;
}

/** As memarea_alloc(), but clears the memory it returns. */
void *
memarea_alloc_zero(memarea_t *area, size_t sz)
{
 void *result = memarea_alloc(area, sz);
 memset(result, 0, sz);
 return result;
}

/** As memdup, but returns the memory from <b>area</b>. */
void *
memarea_memdup(memarea_t *area, const void *s, size_t n)
{
 char *result = memarea_alloc(area, n);
 memcpy(result, s, n);
 return result;
}

/** As strdup, but returns the memory from <b>area</b>. */
char *
memarea_strdup(memarea_t *area, const char *s)
{
 return memarea_memdup(area, s, strlen(s)+1);
}

/** As strndup, but returns the memory from <b>area</b>. */
char *
memarea_strndup(memarea_t *area, const char *s, size_t n)
{
 size_t ln = 0;
 char *result;
 tor_assert(n < SIZE_T_CEILING);
 for (ln = 0; ln < n && s[ln]; ++ln)
   ;
 result = memarea_alloc(area, ln+1);
 memcpy(result, s, ln);
 result[ln]='\0';
 return result;
}

/** Set <b>allocated_out</b> to the number of bytes allocated in <b>area</b>,
* and <b>used_out</b> to the number of bytes currently used. */
void
memarea_get_stats(memarea_t *area, size_t *allocated_out, size_t *used_out)
{
 size_t a = 0, u = 0;
 memarea_chunk_t *chunk;
 for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
   CHECK_SENTINEL(chunk);
   a += CHUNK_HEADER_SIZE + chunk->mem_size;
   tor_assert(chunk->next_mem >= chunk->U_MEM);
   u += CHUNK_HEADER_SIZE + (chunk->next_mem - chunk->U_MEM);
 }
 *allocated_out = a;
 *used_out = u;
}

/** Assert that <b>area</b> is okay. */
void
memarea_assert_ok(memarea_t *area)
{
 memarea_chunk_t *chunk;
 tor_assert(area->first);

 for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
   CHECK_SENTINEL(chunk);
   tor_assert(chunk->next_mem >= chunk->U_MEM);
   tor_assert(chunk->next_mem <=
         (char*) realign_pointer(chunk->U_MEM+chunk->mem_size));
 }
}

#else /* defined(DISABLE_MEMORY_SENTINELS) */

struct memarea_t {
 smartlist_t *pieces;
};

memarea_t *
memarea_new(void)
{
 memarea_t *ma = tor_malloc_zero(sizeof(memarea_t));
 ma->pieces = smartlist_new();
 return ma;
}
void
memarea_drop_all_(memarea_t *area)
{
 memarea_clear(area);
 smartlist_free(area->pieces);
 tor_free(area);
}
void
memarea_clear(memarea_t *area)
{
 SMARTLIST_FOREACH(area->pieces, void *, p, tor_free_(p));
 smartlist_clear(area->pieces);
}
int
memarea_owns_ptr(const memarea_t *area, const void *ptr)
{
 SMARTLIST_FOREACH(area->pieces, const void *, p, if (ptr == p) return 1;);
 return 0;
}

void *
memarea_alloc(memarea_t *area, size_t sz)
{
 void *result = tor_malloc(sz);
 smartlist_add(area->pieces, result);
 return result;
}

void *
memarea_alloc_zero(memarea_t *area, size_t sz)
{
 void *result = tor_malloc_zero(sz);
 smartlist_add(area->pieces, result);
 return result;
}
void *
memarea_memdup(memarea_t *area, const void *s, size_t n)
{
 void *r = memarea_alloc(area, n);
 memcpy(r, s, n);
 return r;
}
char *
memarea_strdup(memarea_t *area, const char *s)
{
 size_t n = strlen(s);
 char *r = memarea_alloc(area, n+1);
 memcpy(r, s, n);
 r[n] = 0;
 return r;
}
char *
memarea_strndup(memarea_t *area, const char *s, size_t n)
{
 size_t ln = strnlen(s, n);
 char *r = memarea_alloc(area, ln+1);
 memcpy(r, s, ln);
 r[ln] = 0;
 return r;
}
void
memarea_get_stats(memarea_t *area,
                 size_t *allocated_out, size_t *used_out)
{
 (void)area;
 *allocated_out = *used_out = 128;
}
void
memarea_assert_ok(memarea_t *area)
{
 (void)area;
}

#endif /* !defined(DISABLE_MEMORY_SENTINELS) */