coregrind/m_mallocfree.c

/*--------------------------------------------------------------------*/
/*--- An implementation of malloc/free which doesn't use sbrk.     ---*/
/*---                                               m_mallocfree.c ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of Valgrind, a dynamic binary instrumentation
   framework.

   Copyright (C) 2000-2008 Julian Seward 
      jseward@acm.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/

#include "pub_core_basics.h"
#include "pub_core_vki.h"
#include "pub_core_debuglog.h"
#include "pub_core_libcbase.h"
#include "pub_core_aspacemgr.h"
#include "pub_core_libcassert.h"
#include "pub_core_libcprint.h"
#include "pub_core_mallocfree.h"
#include "pub_core_options.h"
#include "pub_core_threadstate.h"   // For VG_INVALID_THREADID
#include "pub_core_tooliface.h"
#include "valgrind.h"

//zz#include "memcheck/memcheck.h"

// #define DEBUG_MALLOC      // turn on heavyweight debugging machinery
// #define VERBOSE_MALLOC    // make verbose, esp. in debugging machinery

/* Number and total size of blocks in free queue. Used by mallinfo(). */
Long VG_(free_queue_volume) = 0;
Long VG_(free_queue_length) = 0;

/*------------------------------------------------------------*/
/*--- Main types                                           ---*/
/*------------------------------------------------------------*/

#define N_MALLOC_LISTS     112    // do not change this

// The amount you can ask for is limited only by sizeof(SizeT)...
#define MAX_PSZB              (~((SizeT)0x0))

// Each arena has a sorted array of superblocks, which expands
// dynamically.  This is its initial size.
#define SBLOCKS_SIZE_INITIAL 50

typedef UChar UByte;

/* Layout of an in-use block:

      this block total szB     (sizeof(SizeT) bytes)
      red zone bytes           (depends on Arena.rz_szB, but >= sizeof(void*))
      (payload bytes)
      red zone bytes           (depends on Arena.rz_szB, but >= sizeof(void*))
      this block total szB     (sizeof(SizeT) bytes)

   Layout of a block on the free list:

      this block total szB     (sizeof(SizeT) bytes)
      freelist previous ptr    (sizeof(void*) bytes)
      excess red zone bytes    (if Arena.rz_szB > sizeof(void*))
      (payload bytes)
      excess red zone bytes    (if Arena.rz_szB > sizeof(void*))
      freelist next ptr        (sizeof(void*) bytes)         
      this block total szB     (sizeof(SizeT) bytes)         

   Total size in bytes (bszB) and payload size in bytes (pszB)
   are related by:

      bszB == pszB + 2*sizeof(SizeT) + 2*a->rz_szB

   The minimum overhead per heap block for arenas used by
   the core is:   

      32-bit platforms:  2*4 + 2*4 == 16 bytes
      64-bit platforms:  2*8 + 2*8 == 32 bytes

   In both cases extra overhead may be incurred when rounding the payload
   size up to VG_MIN_MALLOC_SZB.

   Furthermore, both size fields in the block have their least-significant
   bit set if the block is not in use, and unset if it is in use.
   (The bottom 3 or so bits are always free for this because of alignment.)
   A block size of zero is not possible, because a block always has at
   least two SizeTs and two pointers of overhead.  

   Nb: All Block payloads must be VG_MIN_MALLOC_SZB-aligned.  This is
   achieved by ensuring that Superblocks are VG_MIN_MALLOC_SZB-aligned
   (see newSuperblock() for how), and that the lengths of the following
   things are a multiple of VG_MIN_MALLOC_SZB:
   - Superblock admin section lengths (due to elastic padding)
   - Block admin section (low and high) lengths (due to elastic redzones)
   - Block payload lengths (due to req_pszB rounding up)
*/
typedef
   struct {
      // No fields are actually used in this struct, because a Block has
      // many variable sized fields and so can't be accessed
      // meaningfully with normal fields.  So we use access functions all
      // the time.  This struct gives us a type to use, though.  Also, we
      // make sizeof(Block) 1 byte so that we can do arithmetic with the
      // Block* type in increments of 1!
      UByte dummy;
   } 
   Block;

// A superblock.  'padding' is never used, it just ensures that if the
// entire Superblock is aligned to VG_MIN_MALLOC_SZB, then payload_bytes[]
// will be too.  It can add small amounts of padding unnecessarily -- eg.
// 8-bytes on 32-bit machines with an 8-byte VG_MIN_MALLOC_SZB -- because
// it's too hard to make a constant expression that works perfectly in all
// cases.
// payload_bytes[] is made a single big Block when the Superblock is
// created, and then can be split and the splittings remerged, but Blocks
// always cover its entire length -- there's never any unused bytes at the
// end, for example.
typedef
   struct _Superblock {
      SizeT n_payload_bytes;
      void* padding2;
      UByte padding[ VG_MIN_MALLOC_SZB -
                        ((sizeof(struct _Superblock*) + sizeof(SizeT)) %
                         VG_MIN_MALLOC_SZB) ];
      UByte payload_bytes[0];
   }
   Superblock;

// An arena. 'freelist' is a circular, doubly-linked list.  'rz_szB' is
// elastic, in that it can be bigger than asked-for to ensure alignment.
typedef
   struct {
      Char*        name;
      Bool         clientmem;        // Allocates in the client address space?
      SizeT        rz_szB;           // Red zone size in bytes
      SizeT        min_sblock_szB;   // Minimum superblock size in bytes
      Block*       freelist[N_MALLOC_LISTS];
      // A dynamically expanding, ordered array of (pointers to)
      // superblocks in the arena.  If this array is expanded, which
      // is rare, the previous space it occupies is simply abandoned.
      // To avoid having to get yet another block from m_aspacemgr for
      // the first incarnation of this array, the first allocation of
      // it is within this struct.  If it has to be expanded then the
      // new space is acquired from m_aspacemgr as you would expect.
      Superblock** sblocks;
      SizeT        sblocks_size;
      SizeT        sblocks_used;
      Superblock*  sblocks_initial[SBLOCKS_SIZE_INITIAL];
      // Stats only.
      SizeT        bytes_on_loan;
      SizeT        bytes_mmaped;
      SizeT        bytes_on_loan_max;
   }
   Arena;


/*------------------------------------------------------------*/
/*--- Low-level functions for working with Blocks.         ---*/
/*------------------------------------------------------------*/

#define SIZE_T_0x1      ((SizeT)0x1)

// Mark a bszB as in-use, and not in-use, and remove the in-use attribute.
static __inline__
SizeT mk_inuse_bszB ( SizeT bszB )
{
   vg_assert(bszB != 0);
   return bszB & (~SIZE_T_0x1);
}
static __inline__
SizeT mk_free_bszB ( SizeT bszB )
{
   vg_assert(bszB != 0);
   return bszB | SIZE_T_0x1;
}
static __inline__
SizeT mk_plain_bszB ( SizeT bszB )
{
   vg_assert(bszB != 0);
   return bszB & (~SIZE_T_0x1);
}

//---------------------------------------------------------------------------

// Get a block's size as stored, ie with the in-use/free attribute.
static __inline__
SizeT get_bszB_as_is ( Block* b )
{
   UByte* b2     = (UByte*)b;
   SizeT bszB_lo = *(SizeT*)&b2[0];
   SizeT bszB_hi = *(SizeT*)&b2[mk_plain_bszB(bszB_lo) - sizeof(SizeT)];
   vg_assert2(bszB_lo == bszB_hi, 
      "Heap block lo/hi size mismatch: lo = %llu, hi = %llu.\n"
      "Probably caused by overrunning/underrunning a heap block's bounds.\n",
      (ULong)bszB_lo, (ULong)bszB_hi);
   return bszB_lo;
}

// Get a block's plain size, ie. remove the in-use/free attribute.
static __inline__
SizeT get_bszB ( Block* b )
{
   return mk_plain_bszB(get_bszB_as_is(b));
}

// Set the size fields of a block.  bszB may have the in-use/free attribute.
static __inline__
void set_bszB ( Block* b, SizeT bszB )
{
   UByte* b2 = (UByte*)b;
   *(SizeT*)&b2[0]                                   = bszB;
   *(SizeT*)&b2[mk_plain_bszB(bszB) - sizeof(SizeT)] = bszB;
}

//---------------------------------------------------------------------------

// Does this block have the in-use attribute?
static __inline__
Bool is_inuse_block ( Block* b )
{
   SizeT bszB = get_bszB_as_is(b);
   vg_assert(bszB != 0);
   return (0 != (bszB & SIZE_T_0x1)) ? False : True;
}

//---------------------------------------------------------------------------

// Return the lower, upper and total overhead in bytes for a block.
// These are determined purely by which arena the block lives in.
static __inline__
SizeT overhead_szB_lo ( Arena* a )
{
   return sizeof(SizeT) + a->rz_szB;
}
static __inline__
SizeT overhead_szB_hi ( Arena* a )
{
   return a->rz_szB + sizeof(SizeT);
}
static __inline__
SizeT overhead_szB ( Arena* a )
{
   return overhead_szB_lo(a) + overhead_szB_hi(a);
}

//---------------------------------------------------------------------------

// Return the minimum bszB for a block in this arena.  Can have zero-length
// payloads, so it's the size of the admin bytes.
static __inline__
SizeT min_useful_bszB ( Arena* a )
{
   return overhead_szB(a);
}

//---------------------------------------------------------------------------

// Convert payload size <--> block size (both in bytes).
static __inline__
SizeT pszB_to_bszB ( Arena* a, SizeT pszB )
{
   return pszB + overhead_szB(a);
}
static __inline__
SizeT bszB_to_pszB ( Arena* a, SizeT bszB )
{
   vg_assert(bszB >= overhead_szB(a));
   return bszB - overhead_szB(a);
}

//---------------------------------------------------------------------------

// Get a block's payload size.
static __inline__
SizeT get_pszB ( Arena* a, Block* b )
{
   return bszB_to_pszB(a, get_bszB(b));
}

//---------------------------------------------------------------------------

// Given the addr of a block, return the addr of its payload, and vice versa.
static __inline__
UByte* get_block_payload ( Arena* a, Block* b )
{
   UByte* b2 = (UByte*)b;
   return & b2[ overhead_szB_lo(a) ];
}
// Given the addr of a block's payload, return the addr of the block itself.
static __inline__
Block* get_payload_block ( Arena* a, UByte* payload )
{
   return (Block*)&payload[ -overhead_szB_lo(a) ];
}

//---------------------------------------------------------------------------

// Set and get the next and previous link fields of a block.
static __inline__
void set_prev_b ( Block* b, Block* prev_p )
{ 
   UByte* b2 = (UByte*)b;
   *(Block**)&b2[sizeof(SizeT)] = prev_p;
}
static __inline__
void set_next_b ( Block* b, Block* next_p )
{
   UByte* b2 = (UByte*)b;
   *(Block**)&b2[get_bszB(b) - sizeof(SizeT) - sizeof(void*)] = next_p;
}
static __inline__
Block* get_prev_b ( Block* b )
{ 
   UByte* b2 = (UByte*)b;
   return *(Block**)&b2[sizeof(SizeT)];
}
static __inline__
Block* get_next_b ( Block* b )
{ 
   UByte* b2 = (UByte*)b;
   return *(Block**)&b2[get_bszB(b) - sizeof(SizeT) - sizeof(void*)];
}

//---------------------------------------------------------------------------

// Get the block immediately preceding this one in the Superblock.
static __inline__
Block* get_predecessor_block ( Block* b )
{
   UByte* b2 = (UByte*)b;
   SizeT  bszB = mk_plain_bszB( (*(SizeT*)&b2[-sizeof(SizeT)]) );
   return (Block*)&b2[-bszB];
}

//---------------------------------------------------------------------------

// Read and write the lower and upper red-zone bytes of a block.
static __inline__
void set_rz_lo_byte ( Arena* a, Block* b, UInt rz_byteno, UByte v )
{
   UByte* b2 = (UByte*)b;
   b2[sizeof(SizeT) + rz_byteno] = v;
}
static __inline__
void set_rz_hi_byte ( Arena* a, Block* b, UInt rz_byteno, UByte v )
{
   UByte* b2 = (UByte*)b;
   b2[get_bszB(b) - sizeof(SizeT) - rz_byteno - 1] = v;
}
static __inline__
UByte get_rz_lo_byte ( Arena* a, Block* b, UInt rz_byteno )
{
   UByte* b2 = (UByte*)b;
   return b2[sizeof(SizeT) + rz_byteno];
}
static __inline__
UByte get_rz_hi_byte ( Arena* a, Block* b, UInt rz_byteno )
{
   UByte* b2 = (UByte*)b;
   return b2[get_bszB(b) - sizeof(SizeT) - rz_byteno - 1];
}


/*------------------------------------------------------------*/
/*--- Arena management                                     ---*/
/*------------------------------------------------------------*/

#define CORE_ARENA_MIN_SZB    1048576

// The arena structures themselves.
static Arena vg_arena[VG_N_ARENAS];

// Functions external to this module identify arenas using ArenaIds,
// not Arena*s.  This fn converts the former to the latter.
static Arena* arenaId_to_ArenaP ( ArenaId arena )
{
   vg_assert(arena >= 0 && arena < VG_N_ARENAS);
   return & vg_arena[arena];
}

// Initialise an arena.  rz_szB is the minimum redzone size;  it might be
// made bigger to ensure that VG_MIN_MALLOC_SZB is observed.
static
void arena_init ( ArenaId aid, Char* name, SizeT rz_szB, SizeT min_sblock_szB )
{
   SizeT  i;
   Arena* a = arenaId_to_ArenaP(aid);
   
   // Ensure redzones are a reasonable size.  They must always be at least
   // the size of a pointer, for holding the prev/next pointer (see the layout
   // details at the top of this file).
   vg_assert(rz_szB < 128);
   if (rz_szB < sizeof(void*)) rz_szB = sizeof(void*);
   
   vg_assert((min_sblock_szB % VKI_PAGE_SIZE) == 0);
   a->name      = name;
   a->clientmem = ( VG_AR_CLIENT == aid ? True : False );

   // The size of the low and high admin sections in a block must be a
   // multiple of VG_MIN_MALLOC_SZB.  So we round up the asked-for
   // redzone size if necessary to achieve this.
   a->rz_szB = rz_szB;
   while (0 != overhead_szB_lo(a) % VG_MIN_MALLOC_SZB) a->rz_szB++;
   vg_assert(overhead_szB_lo(a) == overhead_szB_hi(a));

   a->min_sblock_szB = min_sblock_szB;
   for (i = 0; i < N_MALLOC_LISTS; i++) a->freelist[i] = NULL;

   a->sblocks           = & a->sblocks_initial[0];
   a->sblocks_size      = SBLOCKS_SIZE_INITIAL;
   a->sblocks_used      = 0;
   a->bytes_on_loan     = 0;
   a->bytes_mmaped      = 0;
   a->bytes_on_loan_max = 0;
   vg_assert(sizeof(a->sblocks_initial) 
             == SBLOCKS_SIZE_INITIAL * sizeof(Superblock*));
}

/* Print vital stats for an arena. */
void VG_(print_all_arena_stats) ( void )
{
   UInt i;
   for (i = 0; i < VG_N_ARENAS; i++) {
      Arena* a = arenaId_to_ArenaP(i);
      VG_(message)(Vg_DebugMsg,
         "%8s: %8d mmap'd, %8d/%8d max/curr",
         a->name, a->bytes_mmaped, a->bytes_on_loan_max, a->bytes_on_loan 
      );
   }
}

/* This library is self-initialising, as it makes this more self-contained,
   less coupled with the outside world.  Hence VG_(arena_malloc)() and
   VG_(arena_free)() below always call ensure_mm_init() to ensure things are
   correctly initialised.  

   We initialise the client arena separately (and later) because the core
   must do non-client allocation before the tool has a chance to set the
   client arena's redzone size.
*/
static Bool     client_inited = False;
static Bool  nonclient_inited = False;

static
void ensure_mm_init ( ArenaId aid )
{
   static SizeT client_rz_szB = 8;     // default: be paranoid

   /* We use checked red zones (of various sizes) for our internal stuff,
      and an unchecked zone of arbitrary size for the client.  Of
      course the client's red zone can be checked by the tool, eg. 
      by using addressibility maps, but not by the mechanism implemented
      here, which merely checks at the time of freeing that the red 
      zone bytes are unchanged.

      Nb: redzone sizes are *minimums*;  they could be made bigger to ensure
      alignment.  Eg. with 8 byte alignment, on 32-bit machines 4 stays as
      4, but 16 becomes 20;  but on 64-bit machines 4 becomes 8, and 16
      stays as 16 --- the extra 4 bytes in both are accounted for by the
      larger prev/next ptr.
   */
   if (VG_AR_CLIENT == aid) {
      Int ar_client_sbszB;
      if (client_inited) {
         // This assertion ensures that a tool cannot try to change the client
         // redzone size with VG_(needs_malloc_replacement)() after this module
         // has done its first allocation from the client arena.
         if (VG_(needs).malloc_replacement)
            vg_assert(client_rz_szB == VG_(tdict).tool_client_redzone_szB);
         return;
      }

      // Check and set the client arena redzone size
      if (VG_(needs).malloc_replacement) {
         client_rz_szB = VG_(tdict).tool_client_redzone_szB;
         // 128 is no special figure, just something not too big
         if (client_rz_szB > 128) {
            VG_(printf)( "\nTool error:\n"
                         "  specified redzone size is too big (%llu)\n", 
                         (ULong)client_rz_szB);
            VG_(exit)(1);
         }
      }
      // Initialise the client arena.  On AIX it's important to have
      // relatively large client blocks so as not to cause excessively
      // fine-grained interleaving of V and C address space.  On Linux
      // this is irrelevant since aspacem can keep the two spaces
      // well apart, but not so on AIX.  On all platforms though, 
      // increasing the superblock size reduces the number of superblocks
      // in the client arena, which makes findSb cheaper.
#     if defined(VGO_aix5)
      ar_client_sbszB = 16777216;
#     else
      ar_client_sbszB = 4194304;
#     endif
      arena_init ( VG_AR_CLIENT,    "client",   client_rz_szB, ar_client_sbszB );
      client_inited = True;

   } else {
      if (nonclient_inited) {
         return;
      }
      // Initialise the non-client arenas
      arena_init ( VG_AR_CORE,      "core",     4,             1048576 );
      arena_init ( VG_AR_TOOL,      "tool",     4,             4194304 );
      arena_init ( VG_AR_DINFO,     "dinfo",    4,             1048576 );
      arena_init ( VG_AR_DEMANGLE,  "demangle", 4,               65536 );
      arena_init ( VG_AR_EXECTXT,   "exectxt",  4,             1048576 );
      arena_init ( VG_AR_ERRORS,    "errors",   4,               65536 );
      arena_init ( VG_AR_TTAUX,     "ttaux",    4,               65536 );
      nonclient_inited = True;
   }

#  ifdef DEBUG_MALLOC
   VG_(printf)("ZZZ1\n");
   VG_(sanity_check_malloc_all)();
   VG_(printf)("ZZZ2\n");
#  endif
}


/*------------------------------------------------------------*/
/*--- Superblock management                                ---*/
/*------------------------------------------------------------*/

void VG_(out_of_memory_NORETURN) ( HChar* who, SizeT szB )
{
   static Bool alreadyCrashing = False;
   ULong tot_alloc = VG_(am_get_anonsize_total)();
   Char* s1 = 
      "\n"
      "    Valgrind's memory management: out of memory:\n"
      "       %s's request for %llu bytes failed.\n"
      "       %llu bytes have already been allocated.\n"
      "    Valgrind cannot continue.  Sorry.\n\n"
      "    There are several possible reasons for this.\n"
      "    - You have some kind of memory limit in place.  Look at the\n"
      "      output of 'ulimit -a'.  Is there a limit on the size of\n"
      "      virtual memory or address space?\n"
      "    - You have run out of swap space.\n"
      "    - Valgrind has a bug.  If you think this is the case or you are\n"
      "    not sure, please let us know and we'll try to fix it.\n"
      "    Please note that programs can take substantially more memory than\n"
      "    normal when running under Valgrind tools, eg. up to twice or\n"
      "    more, depending on the tool.  On a 64-bit machine, Valgrind\n"
      "    should be able to make use of up 32GB memory.  On a 32-bit\n"
      "    machine, Valgrind should be able to use all the memory available\n"
      "    to a single process, up to 4GB if that's how you have your\n"
      "    kernel configured.  Most 32-bit Linux setups allow a maximum of\n"
      "    3GB per process.\n\n"
      "    Whatever the reason, Valgrind cannot continue.  Sorry.\n";

   if (!alreadyCrashing) {
      alreadyCrashing = True;
      VG_(message)(Vg_UserMsg, s1, who, (ULong)szB, tot_alloc);
   } else {
      VG_(debugLog)(0,"mallocfree", s1, who, (ULong)szB, tot_alloc);
   }
   VG_(exit)(1);
}


// Align ptr p upwards to an align-sized boundary.
static
void* align_upwards ( void* p, SizeT align )
{
   Addr a = (Addr)p;
   if ((a % align) == 0) return (void*)a;
   return (void*)(a - (a % align) + align);
}

// If not enough memory available, either aborts (for non-client memory)
// or returns 0 (for client memory).
static
Superblock* newSuperblock ( Arena* a, SizeT cszB )
{
   Superblock* sb;
   SysRes      sres;

   // Take into account admin bytes in the Superblock.
   cszB += sizeof(Superblock);

   if (cszB < a->min_sblock_szB) cszB = a->min_sblock_szB;
   cszB = VG_PGROUNDUP(cszB);

   if (a->clientmem) {
      // client allocation -- return 0 to client if it fails
      sres = VG_(am_sbrk_anon_float_client)
                ( cszB, VKI_PROT_READ|VKI_PROT_WRITE|VKI_PROT_EXEC );
      if (sres.isError)
         return 0;
      sb = (Superblock*)sres.res;
      // Mark this segment as containing client heap.  The leak
      // checker needs to be able to identify such segments so as not
      // to use them as sources of roots during leak checks.
      VG_(am_set_segment_isCH_if_SkAnonC)( 
         (NSegment*) VG_(am_find_nsegment)( (Addr)sb )
      );
   } else {
      // non-client allocation -- abort if it fails
      sres = VG_(am_sbrk_anon_float_valgrind)( cszB );
      if (sres.isError) {
         VG_(out_of_memory_NORETURN)("newSuperblock", cszB);
         /* NOTREACHED */
         sb = NULL; /* keep gcc happy */
      } else {
         sb = (Superblock*)sres.res;
      }
   }
   vg_assert(NULL != sb);
   //zzVALGRIND_MAKE_MEM_UNDEFINED(sb, cszB);
   vg_assert(0 == (Addr)sb % VG_MIN_MALLOC_SZB);
   sb->n_payload_bytes = cszB - sizeof(Superblock);
   a->bytes_mmaped += cszB;
   VG_(debugLog)(1, "mallocfree",
                    "newSuperblock at %p (pszB %7ld) owner %s/%s\n", 
                    sb, sb->n_payload_bytes, 
                    a->clientmem ? "CLIENT" : "VALGRIND", a->name );
   return sb;
}

// Find the superblock containing the given chunk.
static
Superblock* findSb ( Arena* a, Block* b )
{
   SizeT min = 0;
   SizeT max = a->sblocks_used;

   while (min <= max) {
      Superblock * sb; 
      SizeT pos = min + (max - min)/2;

      vg_assert(pos >= 0 && pos < a->sblocks_used);
      sb = a->sblocks[pos];
      if ((Block*)&sb->payload_bytes[0] <= b
          && b < (Block*)&sb->payload_bytes[sb->n_payload_bytes])
      {
         return sb;
      } else if ((Block*)&sb->payload_bytes[0] <= b) {
         min = pos + 1;
      } else {
         max = pos - 1;
      }
   }
   VG_(printf)("findSb: can't find pointer %p in arena '%s'\n",
                b, a->name );
   VG_(core_panic)("findSb: VG_(arena_free)() in wrong arena?");
   return NULL; /*NOTREACHED*/
}


/*------------------------------------------------------------*/
/*--- Functions for working with freelists.                ---*/
/*------------------------------------------------------------*/

// Nb: Determination of which freelist a block lives on is based on the
// payload size, not block size.

// Convert a payload size in bytes to a freelist number.
static
UInt pszB_to_listNo ( SizeT pszB )
{
   SizeT n = pszB / VG_MIN_MALLOC_SZB;
   vg_assert(0 == pszB % VG_MIN_MALLOC_SZB);

   // The first 64 lists hold blocks of size VG_MIN_MALLOC_SZB * list_num.
   // The final 48 hold bigger blocks.
   if (n < 64)   return (UInt)n;
   /* Exponential slope up, factor 1.05 */
   if (n < 67) return 64;
   if (n < 70) return 65;
   if (n < 74) return 66;
   if (n < 77) return 67;
   if (n < 81) return 68;
   if (n < 85) return 69;
   if (n < 90) return 70;
   if (n < 94) return 71;
   if (n < 99) return 72;
   if (n < 104) return 73;
   if (n < 109) return 74;
   if (n < 114) return 75;
   if (n < 120) return 76;
   if (n < 126) return 77;
   if (n < 133) return 78;
   if (n < 139) return 79;
   /* Exponential slope up, factor 1.10 */
   if (n < 153) return 80;
   if (n < 169) return 81;
   if (n < 185) return 82;
   if (n < 204) return 83;
   if (n < 224) return 84;
   if (n < 247) return 85;
   if (n < 272) return 86;
   if (n < 299) return 87;
   if (n < 329) return 88;
   if (n < 362) return 89;
   if (n < 398) return 90;
   if (n < 438) return 91;
   if (n < 482) return 92;
   if (n < 530) return 93;
   if (n < 583) return 94;
   if (n < 641) return 95;
   /* Exponential slope up, factor 1.20 */
   if (n < 770) return 96;
   if (n < 924) return 97;
   if (n < 1109) return 98;
   if (n < 1331) return 99;
   if (n < 1597) return 100;
   if (n < 1916) return 101;
   if (n < 2300) return 102;
   if (n < 2760) return 103;
   if (n < 3312) return 104;
   if (n < 3974) return 105;
   if (n < 4769) return 106;
   if (n < 5723) return 107;
   if (n < 6868) return 108;
   if (n < 8241) return 109;
   if (n < 9890) return 110;
   return 111;
}

// What is the minimum payload size for a given list?
static
SizeT listNo_to_pszB_min ( UInt listNo )
{
   /* Repeatedly computing this function at every request is
      expensive.  Hence at the first call just cache the result for
      every possible argument. */
   static SizeT cache[N_MALLOC_LISTS];
   static Bool  cache_valid = False;
   if (!cache_valid) {
      UInt i;
      for (i = 0; i < N_MALLOC_LISTS; i++) {
         SizeT pszB = 0;
         while (pszB_to_listNo(pszB) < i)
            pszB += VG_MIN_MALLOC_SZB;
         cache[i] = pszB;
      }
      cache_valid = True;
   }
   /* Returned cached answer. */
   vg_assert(listNo <= N_MALLOC_LISTS);
   return cache[listNo];
}

// What is the maximum payload size for a given list?
static
SizeT listNo_to_pszB_max ( UInt listNo )
{
   vg_assert(listNo <= N_MALLOC_LISTS);
   if (listNo == N_MALLOC_LISTS-1) {
      return MAX_PSZB;
   } else {
      return listNo_to_pszB_min(listNo+1) - 1;
   }
}


/* A nasty hack to try and reduce fragmentation.  Try and replace
   a->freelist[lno] with another block on the same list but with a
   lower address, with the idea of attempting to recycle the same
   blocks rather than cruise through the address space. */
static 
void swizzle ( Arena* a, UInt lno )
{
   Block* p_best;
   Block* pp;
   Block* pn;
   UInt   i;

   p_best = a->freelist[lno];
   if (p_best == NULL) return;

   pn = pp = p_best;

   // This loop bound was 20 for a long time, but experiments showed that
   // reducing it to 10 gave the same result in all the tests, and 5 got the
   // same result in 85--100% of cases.  And it's called often enough to be
   // noticeable in programs that allocated a lot.
   for (i = 0; i < 5; i++) {
      pn = get_next_b(pn);
      pp = get_prev_b(pp);
      if (pn < p_best) p_best = pn;
      if (pp < p_best) p_best = pp;
   }
   if (p_best < a->freelist[lno]) {
#     ifdef VERBOSE_MALLOC
      VG_(printf)("retreat by %d\n", a->freelist[lno] - p_best);
#     endif
      a->freelist[lno] = p_best;
   }
}


/*------------------------------------------------------------*/
/*--- Sanity-check/debugging machinery.                    ---*/
/*------------------------------------------------------------*/

#define REDZONE_LO_MASK    0x31
#define REDZONE_HI_MASK    0x7c

// Do some crude sanity checks on a Block.
static 
Bool blockSane ( Arena* a, Block* b )
{
#  define BLEAT(str) VG_(printf)("blockSane: fail -- %s\n",str)
   UInt i;
   // The lo and hi size fields will be checked (indirectly) by the call
   // to get_rz_hi_byte().
   if (!a->clientmem && is_inuse_block(b)) {
      for (i = 0; i < a->rz_szB; i++) {
         if (get_rz_lo_byte(a, b, i) != 
            (UByte)(((Addr)b&0xff) ^ REDZONE_LO_MASK))
               {BLEAT("redzone-lo");return False;}
         if (get_rz_hi_byte(a, b, i) != 
            (UByte)(((Addr)b&0xff) ^ REDZONE_HI_MASK))
               {BLEAT("redzone-hi");return False;}
      }      
   }
   return True;
#  undef BLEAT
}

// Print superblocks (only for debugging).
static 
void ppSuperblocks ( Arena* a )
{
   UInt i, j, blockno = 1;
   SizeT b_bszB;

   for (j = 0; j < a->sblocks_used; ++j) {
      Superblock * sb = a->sblocks[j];

      VG_(printf)( "\n" );
      VG_(printf)( "superblock %d at %p, sb->n_pl_bs = %lu\n",
                   blockno++, sb, sb->n_payload_bytes);
      for (i = 0; i < sb->n_payload_bytes; i += b_bszB) {
         Block* b = (Block*)&sb->payload_bytes[i];
         b_bszB   = get_bszB(b);
         VG_(printf)( "   block at %d, bszB %lu: ", i, b_bszB );
         VG_(printf)( "%s, ", is_inuse_block(b) ? "inuse" : "free");
         VG_(printf)( "%s\n", blockSane(a, b) ? "ok" : "BAD" );
      }
      vg_assert(i == sb->n_payload_bytes);   // no overshoot at end of Sb
   }
   VG_(printf)( "end of superblocks\n\n" );
}

// Sanity check both the superblocks and the chains.
static void sanity_check_malloc_arena ( ArenaId aid )
{
   UInt        i, j, superblockctr, blockctr_sb, blockctr_li;
   UInt        blockctr_sb_free, listno;
   SizeT       b_bszB, b_pszB, list_min_pszB, list_max_pszB;
   Bool        thisFree, lastWasFree, sblockarrOK;
   Block*      b;
   Block*      b_prev;
   SizeT       arena_bytes_on_loan;
   Arena*      a;

#  define BOMB VG_(core_panic)("sanity_check_malloc_arena")

   a = arenaId_to_ArenaP(aid);

   // Check the superblock array.
   sblockarrOK
      = a->sblocks != NULL
        && a->sblocks_size >= SBLOCKS_SIZE_INITIAL
        && a->sblocks_used <= a->sblocks_size
        && (a->sblocks_size == SBLOCKS_SIZE_INITIAL 
            ? (a->sblocks == &a->sblocks_initial[0])
            : (a->sblocks != &a->sblocks_initial[0]));
   if (!sblockarrOK) {
      VG_(printf)("sanity_check_malloc_arena: sblock array BAD\n");
      BOMB;
   }

   // First, traverse all the superblocks, inspecting the Blocks in each.
   superblockctr = blockctr_sb = blockctr_sb_free = 0;
   arena_bytes_on_loan = 0;
   for (j = 0; j < a->sblocks_used; ++j) {
      Superblock * sb = a->sblocks[j];
      lastWasFree = False;
      superblockctr++;
      for (i = 0; i < sb->n_payload_bytes; i += mk_plain_bszB(b_bszB)) {
         blockctr_sb++;
         b     = (Block*)&sb->payload_bytes[i];
         b_bszB = get_bszB_as_is(b);
         if (!blockSane(a, b)) {
            VG_(printf)("sanity_check_malloc_arena: sb %p, block %d "
                        "(bszB %lu):  BAD\n", sb, i, b_bszB );
            BOMB;
         }
         thisFree = !is_inuse_block(b);
         if (thisFree && lastWasFree) {
            VG_(printf)("sanity_check_malloc_arena: sb %p, block %d "
                        "(bszB %lu): UNMERGED FREES\n", sb, i, b_bszB );
            BOMB;
         }
         if (thisFree) blockctr_sb_free++;
         if (!thisFree)
            arena_bytes_on_loan += bszB_to_pszB(a, b_bszB);
         lastWasFree = thisFree;
      }
      if (i > sb->n_payload_bytes) {
         VG_(printf)( "sanity_check_malloc_arena: sb %p: last block "
                      "overshoots end\n", sb);
         BOMB;
      }
   }

   if (arena_bytes_on_loan != a->bytes_on_loan) {
#     ifdef VERBOSE_MALLOC
      VG_(printf)( "sanity_check_malloc_arena: a->bytes_on_loan %d, "
                   "arena_bytes_on_loan %d: "
                   "MISMATCH\n", a->bytes_on_loan, arena_bytes_on_loan);
#     endif
      ppSuperblocks(a);
      BOMB;
   }

   /* Second, traverse each list, checking that the back pointers make
      sense, counting blocks encountered, and checking that each block
      is an appropriate size for this list. */
   blockctr_li = 0;
   for (listno = 0; listno < N_MALLOC_LISTS; listno++) {
      list_min_pszB = listNo_to_pszB_min(listno);
      list_max_pszB = listNo_to_pszB_max(listno);
      b = a->freelist[listno];
      if (b == NULL) continue;
      while (True) {
         b_prev = b;
         b = get_next_b(b);
         if (get_prev_b(b) != b_prev) {
            VG_(printf)( "sanity_check_malloc_arena: list %d at %p: "
                         "BAD LINKAGE\n",
                         listno, b );
            BOMB;
         }
         b_pszB = get_pszB(a, b);
         if (b_pszB < list_min_pszB || b_pszB > list_max_pszB) {
            VG_(printf)(
               "sanity_check_malloc_arena: list %d at %p: "
               "WRONG CHAIN SIZE %luB (%luB, %luB)\n",
               listno, b, b_pszB, list_min_pszB, list_max_pszB );
            BOMB;
         }
         blockctr_li++;
         if (b == a->freelist[listno]) break;
      }
   }

   if (blockctr_sb_free != blockctr_li) {
#     ifdef VERBOSE_MALLOC
      VG_(printf)( "sanity_check_malloc_arena: BLOCK COUNT MISMATCH "
                   "(via sbs %d, via lists %d)\n",
                   blockctr_sb_free, blockctr_li );
#     endif
      ppSuperblocks(a);
      BOMB;
   }

   if (VG_(clo_verbosity) > 2) 
      VG_(message)(Vg_DebugMsg,
                   "%8s: %2d sbs, %5d bs, %2d/%-2d free bs, "
                   "%7d mmap, %7d loan", 
                   a->name,
                   superblockctr,
                   blockctr_sb, blockctr_sb_free, blockctr_li, 
                   a->bytes_mmaped, a->bytes_on_loan);   
#  undef BOMB
}


void VG_(sanity_check_malloc_all) ( void )
{
   UInt i;
   for (i = 0; i < VG_N_ARENAS; i++) {
      if (i == VG_AR_CLIENT && !client_inited)
         continue;
      sanity_check_malloc_arena ( i );
   }
}


/*------------------------------------------------------------*/
/*--- Creating and deleting blocks.                        ---*/
/*------------------------------------------------------------*/

// Mark the bytes at b .. b+bszB-1 as not in use, and add them to the
// relevant free list.

static
void mkFreeBlock ( Arena* a, Block* b, SizeT bszB, UInt b_lno )
{
   SizeT pszB = bszB_to_pszB(a, bszB);
   vg_assert(b_lno == pszB_to_listNo(pszB));
   //zzVALGRIND_MAKE_MEM_UNDEFINED(b, bszB);
   // Set the size fields and indicate not-in-use.
   set_bszB(b, mk_free_bszB(bszB));

   // Add to the relevant list.
   if (a->freelist[b_lno] == NULL) {
      set_prev_b(b, b);
      set_next_b(b, b);
      a->freelist[b_lno] = b;
   } else {
      Block* b_prev = get_prev_b(a->freelist[b_lno]);
      Block* b_next = a->freelist[b_lno];
      set_next_b(b_prev, b);
      set_prev_b(b_next, b);
      set_next_b(b, b_next);
      set_prev_b(b, b_prev);
   }
#  ifdef DEBUG_MALLOC
   (void)blockSane(a,b);
#  endif
}

// Mark the bytes at b .. b+bszB-1 as in use, and set up the block
// appropriately.
static
void mkInuseBlock ( Arena* a, Block* b, SizeT bszB )
{
   UInt i;
   vg_assert(bszB >= min_useful_bszB(a));
   //zzVALGRIND_MAKE_MEM_UNDEFINED(b, bszB);
   set_bszB(b, mk_inuse_bszB(bszB));
   set_prev_b(b, NULL);    // Take off freelist
   set_next_b(b, NULL);    // ditto
   if (!a->clientmem) {
      for (i = 0; i < a->rz_szB; i++) {
         set_rz_lo_byte(a, b, i, (UByte)(((Addr)b&0xff) ^ REDZONE_LO_MASK));
         set_rz_hi_byte(a, b, i, (UByte)(((Addr)b&0xff) ^ REDZONE_HI_MASK));
      }
   }
#  ifdef DEBUG_MALLOC
   (void)blockSane(a,b);
#  endif
}

// Remove a block from a given list.  Does no sanity checking.
static
void unlinkBlock ( Arena* a, Block* b, UInt listno )
{
   vg_assert(listno < N_MALLOC_LISTS);
   if (get_prev_b(b) == b) {
      // Only one element in the list; treat it specially.
      vg_assert(get_next_b(b) == b);
      a->freelist[listno] = NULL;
   } else {
      Block* b_prev = get_prev_b(b);
      Block* b_next = get_next_b(b);
      a->freelist[listno] = b_prev;
      set_next_b(b_prev, b_next);
      set_prev_b(b_next, b_prev);
      swizzle ( a, listno );
   }
   set_prev_b(b, NULL);
   set_next_b(b, NULL);
}


/*------------------------------------------------------------*/
/*--- Core-visible functions.                              ---*/
/*------------------------------------------------------------*/

// Align the request size.
static __inline__
SizeT align_req_pszB ( SizeT req_pszB )
{
   SizeT n = VG_MIN_MALLOC_SZB-1;
   return ((req_pszB + n) & (~n));
}

void* VG_(arena_malloc) ( ArenaId aid, SizeT req_pszB )
{
   SizeT       req_bszB, frag_bszB, b_bszB;
   UInt        lno, i;
   Superblock* new_sb;
   Block*      b = NULL;
   Arena*      a;
   void*       v;

   ensure_mm_init(aid);
   a = arenaId_to_ArenaP(aid);

   vg_assert(req_pszB < MAX_PSZB);
   req_pszB = align_req_pszB(req_pszB);
   req_bszB = pszB_to_bszB(a, req_pszB);

   // Scan through all the big-enough freelists for a block.
   //
   // Nb: this scanning might be expensive in some cases.  Eg. if you
   // allocate lots of small objects without freeing them, but no
   // medium-sized objects, it will repeatedly scanning through the whole
   // list, and each time not find any free blocks until the last element.
   //
   // If this becomes a noticeable problem... the loop answers the question
   // "where is the first nonempty list above me?"  And most of the time,
   // you ask the same question and get the same answer.  So it would be
   // good to somehow cache the results of previous searches.
   // One possibility is an array (with N_MALLOC_LISTS elements) of
   // shortcuts.  shortcut[i] would give the index number of the nearest
   // larger list above list i which is non-empty.  Then this loop isn't
   // necessary.  However, we'd have to modify some section [ .. i-1] of the
   // shortcut array every time a list [i] changes from empty to nonempty or
   // back.  This would require care to avoid pathological worst-case
   // behaviour.
   //
   for (lno = pszB_to_listNo(req_pszB); lno < N_MALLOC_LISTS; lno++) {
      b = a->freelist[lno];
      if (NULL == b) continue;   // If this list is empty, try the next one.
      while (True) {
         b_bszB = get_bszB(b);
         if (b_bszB >= req_bszB) goto obtained_block;    // success!
         b = get_next_b(b);
         if (b == a->freelist[lno]) break;   // traversed entire freelist
      }
   }

   // If we reach here, no suitable block found, allocate a new superblock
   vg_assert(lno == N_MALLOC_LISTS);
   new_sb = newSuperblock(a, req_bszB);
   if (NULL == new_sb) {
      // Should only fail if for client, otherwise, should have aborted
      // already.
      vg_assert(VG_AR_CLIENT == aid);
      return NULL;
   }

   vg_assert(a->sblocks_used <= a->sblocks_size);
   if (a->sblocks_used == a->sblocks_size) {
      Superblock ** array;
      SysRes sres = VG_(am_sbrk_anon_float_valgrind)(sizeof(Superblock *) *
                                                     a->sblocks_size * 2);
      if (sres.isError) {
         VG_(out_of_memory_NORETURN)("arena_init", sizeof(Superblock *) * 
                                                   a->sblocks_size * 2);
         /* NOTREACHED */
      }
      array = (Superblock**) sres.res;
      for (i = 0; i < a->sblocks_used; ++i) array[i] = a->sblocks[i];

      a->sblocks_size *= 2;
      a->sblocks = array;
      VG_(debugLog)(1, "mallocfree", 
                       "sblock array for arena `%s' resized to %ld\n", 
                       a->name, a->sblocks_size);
   }

   vg_assert(a->sblocks_used < a->sblocks_size);
   
   i = a->sblocks_used;
   while (i > 0) {
      if (a->sblocks[i-1] > new_sb) {
         a->sblocks[i] = a->sblocks[i-1];
      } else {
         break;
      }
      --i;
   }   
   a->sblocks[i] = new_sb;
   a->sblocks_used++;

   b = (Block*)&new_sb->payload_bytes[0];
   lno = pszB_to_listNo(bszB_to_pszB(a, new_sb->n_payload_bytes));
   mkFreeBlock ( a, b, new_sb->n_payload_bytes, lno);
   // fall through

  obtained_block:
   // Ok, we can allocate from b, which lives in list lno.
   vg_assert(b != NULL);
   vg_assert(lno < N_MALLOC_LISTS);
   vg_assert(a->freelist[lno] != NULL);
   b_bszB = get_bszB(b);
   // req_bszB is the size of the block we are after.  b_bszB is the
   // size of what we've actually got. */
   vg_assert(b_bszB >= req_bszB);

   // Could we split this block and still get a useful fragment?
   frag_bszB = b_bszB - req_bszB;
   if (frag_bszB >= min_useful_bszB(a)) {
      // Yes, split block in two, put the fragment on the appropriate free
      // list, and update b_bszB accordingly.
      // printf( "split %dB into %dB and %dB\n", b_bszB, req_bszB, frag_bszB );
      unlinkBlock(a, b, lno);
      mkInuseBlock(a, b, req_bszB);
      mkFreeBlock(a, &b[req_bszB], frag_bszB, 
                     pszB_to_listNo(bszB_to_pszB(a, frag_bszB)));
      b_bszB = get_bszB(b);
   } else {
      // No, mark as in use and use as-is.
      unlinkBlock(a, b, lno);
      mkInuseBlock(a, b, b_bszB);
   }

   // Update stats
   a->bytes_on_loan += bszB_to_pszB(a, b_bszB);
   if (a->bytes_on_loan > a->bytes_on_loan_max)
      a->bytes_on_loan_max = a->bytes_on_loan;

#  ifdef DEBUG_MALLOC
   sanity_check_malloc_arena(aid);
#  endif

   v = get_block_payload(a, b);
   vg_assert( (((Addr)v) & (VG_MIN_MALLOC_SZB-1)) == 0 );

   /* VALGRIND_MALLOCLIKE_BLOCK(v, req_pszB, 0, False); */

   /* For debugging/testing purposes, fill the newly allocated area
      with a definite value in an attempt to shake out any
      uninitialised uses of the data (by V core / V tools, not by the
      client).  Testing on 25 Nov 07 with the values 0x00, 0xFF, 0x55,
      0xAA showed no differences in the regression tests on
      amd64-linux.  Note, is disabled by default. */
   if (0 && aid != VG_AR_CLIENT)
      VG_(memset)(v, 0xAA, (SizeT)req_pszB);

   return v;
}

 
void VG_(arena_free) ( ArenaId aid, void* ptr )
{
   Superblock* sb;
   UByte*      sb_start;
   UByte*      sb_end;
   Block*      other_b;
   Block*      b;
   SizeT       b_bszB, b_pszB, other_bszB;
   UInt        b_listno;
   Arena*      a;

   ensure_mm_init(aid);
   a = arenaId_to_ArenaP(aid);

   if (ptr == NULL) {
      return;
   }
      
   b = get_payload_block(a, ptr);

   /* If this is one of V's areas, check carefully the block we're
      getting back.  This picks up simple block-end overruns. */
   if (aid != VG_AR_CLIENT)
      vg_assert(blockSane(a, b));

   b_bszB   = get_bszB(b);
   b_pszB   = bszB_to_pszB(a, b_bszB);
   sb       = findSb( a, b );
   sb_start = &sb->payload_bytes[0];
   sb_end   = &sb->payload_bytes[sb->n_payload_bytes - 1];

   a->bytes_on_loan -= b_pszB;

   /* If this is one of V's areas, fill it up with junk to enhance the
      chances of catching any later reads of it.  Note, 0xDD is
      carefully chosen junk :-), in that: (1) 0xDDDDDDDD is an invalid
      and non-word-aligned address on most systems, and (2) 0xDD is a
      value which is unlikely to be generated by the new compressed
      Vbits representation for memcheck. */
   if (aid != VG_AR_CLIENT)
      VG_(memset)(ptr, 0xDD, (SizeT)b_pszB);

   // Put this chunk back on a list somewhere.
   b_listno = pszB_to_listNo(b_pszB);
   mkFreeBlock( a, b, b_bszB, b_listno );

   // See if this block can be merged with its successor.
   // First test if we're far enough before the superblock's end to possibly
   // have a successor.
   other_b = b + b_bszB;
   if (other_b+min_useful_bszB(a)-1 <= (Block*)sb_end) {
      // Ok, we have a successor, merge if it's not in use.
      other_bszB = get_bszB(other_b);
      if (!is_inuse_block(other_b)) {
         // VG_(printf)( "merge-successor\n");
#        ifdef DEBUG_MALLOC
         vg_assert(blockSane(a, other_b));
#        endif
         unlinkBlock( a, b, b_listno );
         unlinkBlock( a, other_b, pszB_to_listNo(bszB_to_pszB(a,other_bszB)) );
         b_bszB += other_bszB;
         b_listno = pszB_to_listNo(bszB_to_pszB(a, b_bszB));
         mkFreeBlock( a, b, b_bszB, b_listno );
      }
   } else {
      // Not enough space for successor: check that b is the last block
      // ie. there are no unused bytes at the end of the Superblock.
      vg_assert(other_b-1 == (Block*)sb_end);
   }

   // Then see if this block can be merged with its predecessor.
   // First test if we're far enough after the superblock's start to possibly
   // have a predecessor.
   if (b >= (Block*)sb_start + min_useful_bszB(a)) {
      // Ok, we have a predecessor, merge if it's not in use.
      other_b = get_predecessor_block( b );
      other_bszB = get_bszB(other_b);
      if (!is_inuse_block(other_b)) {
         // VG_(printf)( "merge-predecessor\n");
         unlinkBlock( a, b, b_listno );
         unlinkBlock( a, other_b, pszB_to_listNo(bszB_to_pszB(a, other_bszB)) );
         b = other_b;
         b_bszB += other_bszB;
         b_listno = pszB_to_listNo(bszB_to_pszB(a, b_bszB));
         mkFreeBlock( a, b, b_bszB, b_listno );
      }
   } else {
      // Not enough space for predecessor: check that b is the first block,
      // ie. there are no unused bytes at the start of the Superblock.
      vg_assert((Block*)sb_start == b);
   }

#  ifdef DEBUG_MALLOC
   sanity_check_malloc_arena(aid);
#  endif

   //zzVALGRIND_FREELIKE_BLOCK(ptr, 0);
}


/*
   The idea for malloc_aligned() is to allocate a big block, base, and
   then split it into two parts: frag, which is returned to the the
   free pool, and align, which is the bit we're really after.  Here's
   a picture.  L and H denote the block lower and upper overheads, in
   bytes.  The details are gruesome.  Note it is slightly complicated
   because the initial request to generate base may return a bigger
   block than we asked for, so it is important to distinguish the base
   request size and the base actual size.

   frag_b                   align_b
   |                        |
   |    frag_p              |    align_p
   |    |                   |    |
   v    v                   v    v

   +---+                +---+---+               +---+
   | L |----------------| H | L |---------------| H |
   +---+                +---+---+               +---+

   ^    ^                        ^
   |    |                        :
   |    base_p                   this addr must be aligned
   |
   base_b

   .    .               .   .   .               .   .
   <------ frag_bszB ------->   .               .   .
   .    <------------- base_pszB_act ----------->   .
   .    .               .   .   .               .   .

*/
void* VG_(arena_memalign) ( ArenaId aid, SizeT req_alignB, SizeT req_pszB )
{
   SizeT  base_pszB_req, base_pszB_act, frag_bszB;
   Block  *base_b, *align_b;
   UByte  *base_p, *align_p;
   SizeT  saved_bytes_on_loan;
   Arena* a;

   ensure_mm_init(aid);
   a = arenaId_to_ArenaP(aid);

   vg_assert(req_pszB < MAX_PSZB);

   // Check that the requested alignment seems reasonable; that is, is
   // a power of 2.
   if (req_alignB < VG_MIN_MALLOC_SZB
       || req_alignB > 1048576
       || VG_(log2)( req_alignB ) == -1 /* not a power of 2 */) {
      VG_(printf)("VG_(arena_memalign)(%p, %lu, %lu)\nbad alignment", 
                  a, req_alignB, req_pszB );
      VG_(core_panic)("VG_(arena_memalign)");
      /*NOTREACHED*/
   }
   // Paranoid
   vg_assert(req_alignB % VG_MIN_MALLOC_SZB == 0);

   /* Required payload size for the aligned chunk. */
   req_pszB = align_req_pszB(req_pszB);
   
   /* Payload size to request for the big block that we will split up. */
   base_pszB_req = req_pszB + min_useful_bszB(a) + req_alignB;

   /* Payload ptr for the block we are going to split.  Note this
      changes a->bytes_on_loan; we save and restore it ourselves. */
   saved_bytes_on_loan = a->bytes_on_loan;
   base_p = VG_(arena_malloc) ( aid, base_pszB_req );
   a->bytes_on_loan = saved_bytes_on_loan;

   /* Give up if we couldn't allocate enough space */
   if (base_p == 0)
      return 0;

   /* Block ptr for the block we are going to split. */
   base_b = get_payload_block ( a, base_p );

   /* Pointer to the payload of the aligned block we are going to
      return.  This has to be suitably aligned. */
   align_p = align_upwards ( base_b + 2 * overhead_szB_lo(a)
                                    + overhead_szB_hi(a),
                             req_alignB );
   align_b = get_payload_block(a, align_p);

   /* The block size of the fragment we will create.  This must be big
      enough to actually create a fragment. */
   frag_bszB = align_b - base_b;

   vg_assert(frag_bszB >= min_useful_bszB(a));

   /* The actual payload size of the block we are going to split. */
   base_pszB_act = get_pszB(a, base_b);

   /* Create the fragment block, and put it back on the relevant free list. */
   mkFreeBlock ( a, base_b, frag_bszB,
                 pszB_to_listNo(bszB_to_pszB(a, frag_bszB)) );

   /* Create the aligned block. */
   mkInuseBlock ( a, align_b,
                  base_p + base_pszB_act 
                         + overhead_szB_hi(a) - (UByte*)align_b );

   /* Final sanity checks. */
   vg_assert( is_inuse_block(get_payload_block(a, align_p)) );

   vg_assert(req_pszB <= get_pszB(a, get_payload_block(a, align_p)));

   a->bytes_on_loan += get_pszB(a, get_payload_block(a, align_p));
   if (a->bytes_on_loan > a->bytes_on_loan_max)
      a->bytes_on_loan_max = a->bytes_on_loan;

#  ifdef DEBUG_MALLOC
   sanity_check_malloc_arena(aid);
#  endif

   vg_assert( (((Addr)align_p) % req_alignB) == 0 );

   //zzVALGRIND_MALLOCLIKE_BLOCK(align_p, req_pszB, 0, False);

   return align_p;
}


// The ThreadId doesn't matter, it's not used.
SizeT VG_(arena_payload_szB) ( ThreadId tid, ArenaId aid, void* ptr )
{
   Arena* a = arenaId_to_ArenaP(aid);
   Block* b = get_payload_block(a, ptr);
   return get_pszB(a, b);
}


// Implementation of mallinfo(). There is no recent standard that defines
// the behavior of mallinfo(). The meaning of the fields in struct mallinfo
// is as follows:
//
//     struct mallinfo  {
//                int arena;     /* total space in arena            */
//                int ordblks;   /* number of ordinary blocks       */
//                int smblks;    /* number of small blocks          */
//                int hblks;     /* number of holding blocks        */
//                int hblkhd;    /* space in holding block headers  */
//                int usmblks;   /* space in small blocks in use    */
//                int fsmblks;   /* space in free small blocks      */
//                int uordblks;  /* space in ordinary blocks in use */
//                int fordblks;  /* space in free ordinary blocks   */
//                int keepcost;  /* space penalty if keep option    */
//                               /* is used                         */
//        };
//
// The glibc documentation about mallinfo (which is somewhat outdated) can
// be found here:
// http://www.gnu.org/software/libtool/manual/libc/Statistics-of-Malloc.html
//
// See also http://bugs.kde.org/show_bug.cgi?id=160956.
//
// Regarding the implementation of VG_(mallinfo)(): we cannot return the
// whole struct as the library function does, because this is called by a
// client request.  So instead we use a pointer to do call by reference.
void VG_(mallinfo) ( ThreadId tid, struct vg_mallinfo* mi )
{
   UInt   i, free_blocks, free_blocks_size;
   Arena* a = arenaId_to_ArenaP(VG_AR_CLIENT);

   // Traverse free list and calculate free blocks statistics.
   // This may seem slow but glibc works the same way.
   free_blocks_size = free_blocks = 0;
   for (i = 0; i < N_MALLOC_LISTS; i++) {
      Block* b = a->freelist[i];
      if (b == NULL) continue;
      for (;;) {
         free_blocks++;
         free_blocks_size += get_pszB(a, b);
         b = get_next_b(b);
         if (b == a->freelist[i]) break;
      }
   }

   // We don't have fastbins so smblks & fsmblks are always 0. Also we don't
   // have a separate mmap allocator so set hblks & hblkhd to 0.
   mi->arena    = a->bytes_mmaped;
   mi->ordblks  = free_blocks + VG_(free_queue_length);
   mi->smblks   = 0;
   mi->hblks    = 0;
   mi->hblkhd   = 0;
   mi->usmblks  = 0;
   mi->fsmblks  = 0;
   mi->uordblks = a->bytes_on_loan - VG_(free_queue_volume);
   mi->fordblks = free_blocks_size + VG_(free_queue_volume);
   mi->keepcost = 0; // may want some value in here
}


/*------------------------------------------------------------*/
/*--- Services layered on top of malloc/free.              ---*/
/*------------------------------------------------------------*/

void* VG_(arena_calloc) ( ArenaId aid, SizeT nmemb, SizeT bytes_per_memb )
{
   SizeT  size;
   UChar* p;

   size = nmemb * bytes_per_memb;
   vg_assert(size >= nmemb && size >= bytes_per_memb);// check against overflow

   p = VG_(arena_malloc) ( aid, size );

   VG_(memset)(p, 0, size);

   //zzVALGRIND_MALLOCLIKE_BLOCK(p, size, 0, True);

   return p;
}


void* VG_(arena_realloc) ( ArenaId aid, void* ptr, SizeT req_pszB )
{
   Arena* a;
   SizeT  old_pszB;
   UChar  *p_new;
   Block* b;

   ensure_mm_init(aid);
   a = arenaId_to_ArenaP(aid);

   vg_assert(req_pszB < MAX_PSZB);

   b = get_payload_block(a, ptr);
   vg_assert(blockSane(a, b));

   vg_assert(is_inuse_block(b));
   old_pszB = get_pszB(a, b);

   if (req_pszB <= old_pszB) {
      return ptr;
   }

   p_new = VG_(arena_malloc) ( aid, req_pszB );
      
   VG_(memcpy)(p_new, ptr, old_pszB);

   VG_(arena_free)(aid, ptr);

   return p_new;
}


/* Inline just for the wrapper VG_(strdup) below */
__inline__ Char* VG_(arena_strdup) ( ArenaId aid, const Char* s )
{
   Int   i;
   Int   len;
   Char* res;

   if (s == NULL)
      return NULL;

   len = VG_(strlen)(s) + 1;
   res = VG_(arena_malloc) (aid, len);

   for (i = 0; i < len; i++)
      res[i] = s[i];
   return res;
}


/*------------------------------------------------------------*/
/*--- Tool-visible functions.                              ---*/
/*------------------------------------------------------------*/

// All just wrappers to avoid exposing arenas to tools.

void* VG_(malloc) ( SizeT nbytes )
{
   return VG_(arena_malloc) ( VG_AR_TOOL, nbytes );
}

void  VG_(free) ( void* ptr )
{
   VG_(arena_free) ( VG_AR_TOOL, ptr );
}

void* VG_(calloc) ( SizeT nmemb, SizeT bytes_per_memb )
{
   return VG_(arena_calloc) ( VG_AR_TOOL, nmemb, bytes_per_memb );
}

void* VG_(realloc) ( void* ptr, SizeT size )
{
   return VG_(arena_realloc) ( VG_AR_TOOL, ptr, size );
}

Char* VG_(strdup) ( const Char* s )
{
   return VG_(arena_strdup) ( VG_AR_TOOL, s ); 
}

// Useful for querying user blocks.           
SizeT VG_(malloc_usable_size) ( void* p )                    
{                                                            
   return VG_(arena_payload_szB)(VG_INVALID_THREADID, VG_AR_CLIENT, p);    
}                                                            
  

/*--------------------------------------------------------------------*/
/*--- end                                                          ---*/
/*--------------------------------------------------------------------*/