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// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
/* Copyright (c) 2006, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
// A low-level allocator that can be used by other low-level
// modules without introducing dependency cycles.
// This allocator is slow and wasteful of memory;
// it should not be used when performance is key.
#include "base/low_level_alloc.h"
#include "base/dynamic_annotations.h"
#include "base/spinlock.h"
#include "base/logging.h"
#include "malloc_hook-inl.h"
#include <gperftools/malloc_hook.h>
#include <errno.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_MMAP
#include <sys/mman.h>
#endif
#include <new> // for placement-new
// On systems (like freebsd) that don't define MAP_ANONYMOUS, use the old
// form of the name instead.
#ifndef MAP_ANONYMOUS
# define MAP_ANONYMOUS MAP_ANON
#endif
// A first-fit allocator with amortized logarithmic free() time.
LowLevelAlloc::PagesAllocator::~PagesAllocator() {
}
// ---------------------------------------------------------------------------
static const int kMaxLevel = 30;
// We put this class-only struct in a namespace to avoid polluting the
// global namespace with this struct name (thus risking an ODR violation).
namespace low_level_alloc_internal {
// This struct describes one allocated block, or one free block.
struct AllocList {
struct Header {
intptr_t size; // size of entire region, including this field. Must be
// first. Valid in both allocated and unallocated blocks
intptr_t magic; // kMagicAllocated or kMagicUnallocated xor this
LowLevelAlloc::Arena *arena; // pointer to parent arena
void *dummy_for_alignment; // aligns regions to 0 mod 2*sizeof(void*)
} header;
// Next two fields: in unallocated blocks: freelist skiplist data
// in allocated blocks: overlaps with client data
int levels; // levels in skiplist used
AllocList *next[kMaxLevel]; // actually has levels elements.
// The AllocList node may not have room for
// all kMaxLevel entries. See max_fit in
// LLA_SkiplistLevels()
};
}
using low_level_alloc_internal::AllocList;
// ---------------------------------------------------------------------------
// A trivial skiplist implementation. This is used to keep the freelist
// in address order while taking only logarithmic time per insert and delete.
// An integer approximation of log2(size/base)
// Requires size >= base.
static int IntLog2(size_t size, size_t base) {
int result = 0;
for (size_t i = size; i > base; i >>= 1) { // i == floor(size/2**result)
result++;
}
// floor(size / 2**result) <= base < floor(size / 2**(result-1))
// => log2(size/(base+1)) <= result < 1+log2(size/base)
// => result ~= log2(size/base)
return result;
}
// Return a random integer n: p(n)=1/(2**n) if 1 <= n; p(n)=0 if n < 1.
static int Random() {
static uint32 r = 1; // no locking---it's not critical
ANNOTATE_BENIGN_RACE(&r, "benign race, not critical.");
int result = 1;
while ((((r = r*1103515245 + 12345) >> 30) & 1) == 0) {
result++;
}
return result;
}
// Return a number of skiplist levels for a node of size bytes, where
// base is the minimum node size. Compute level=log2(size / base)+n
// where n is 1 if random is false and otherwise a random number generated with
// the standard distribution for a skiplist: See Random() above.
// Bigger nodes tend to have more skiplist levels due to the log2(size / base)
// term, so first-fit searches touch fewer nodes. "level" is clipped so
// level<kMaxLevel and next[level-1] will fit in the node.
// 0 < LLA_SkiplistLevels(x,y,false) <= LLA_SkiplistLevels(x,y,true) < kMaxLevel
static int LLA_SkiplistLevels(size_t size, size_t base, bool random) {
// max_fit is the maximum number of levels that will fit in a node for the
// given size. We can't return more than max_fit, no matter what the
// random number generator says.
int max_fit = (size-OFFSETOF_MEMBER(AllocList, next)) / sizeof (AllocList *);
int level = IntLog2(size, base) + (random? Random() : 1);
if (level > max_fit) level = max_fit;
if (level > kMaxLevel-1) level = kMaxLevel - 1;
RAW_CHECK(level >= 1, "block not big enough for even one level");
return level;
}
// Return "atleast", the first element of AllocList *head s.t. *atleast >= *e.
// For 0 <= i < head->levels, set prev[i] to "no_greater", where no_greater
// points to the last element at level i in the AllocList less than *e, or is
// head if no such element exists.
static AllocList *LLA_SkiplistSearch(AllocList *head,
AllocList *e, AllocList **prev) {
AllocList *p = head;
for (int level = head->levels - 1; level >= 0; level--) {
for (AllocList *n; (n = p->next[level]) != 0 && n < e; p = n) {
}
prev[level] = p;
}
return (head->levels == 0) ? 0 : prev[0]->next[0];
}
// Insert element *e into AllocList *head. Set prev[] as LLA_SkiplistSearch.
// Requires that e->levels be previously set by the caller (using
// LLA_SkiplistLevels())
static void LLA_SkiplistInsert(AllocList *head, AllocList *e,
AllocList **prev) {
LLA_SkiplistSearch(head, e, prev);
for (; head->levels < e->levels; head->levels++) { // extend prev pointers
prev[head->levels] = head; // to all *e's levels
}
for (int i = 0; i != e->levels; i++) { // add element to list
e->next[i] = prev[i]->next[i];
prev[i]->next[i] = e;
}
}
// Remove element *e from AllocList *head. Set prev[] as LLA_SkiplistSearch().
// Requires that e->levels be previous set by the caller (using
// LLA_SkiplistLevels())
static void LLA_SkiplistDelete(AllocList *head, AllocList *e,
AllocList **prev) {
AllocList *found = LLA_SkiplistSearch(head, e, prev);
RAW_CHECK(e == found, "element not in freelist");
for (int i = 0; i != e->levels && prev[i]->next[i] == e; i++) {
prev[i]->next[i] = e->next[i];
}
while (head->levels > 0 && head->next[head->levels - 1] == 0) {
head->levels--; // reduce head->levels if level unused
}
}
// ---------------------------------------------------------------------------
// Arena implementation
struct LowLevelAlloc::Arena {
Arena() : mu(SpinLock::LINKER_INITIALIZED) {} // does nothing; for static init
explicit Arena(int) : pagesize(0) {} // set pagesize to zero explicitly
// for non-static init
SpinLock mu; // protects freelist, allocation_count,
// pagesize, roundup, min_size
AllocList freelist; // head of free list; sorted by addr (under mu)
int32 allocation_count; // count of allocated blocks (under mu)
int32 flags; // flags passed to NewArena (ro after init)
size_t pagesize; // ==getpagesize() (init under mu, then ro)
size_t roundup; // lowest power of 2 >= max(16,sizeof (AllocList))
// (init under mu, then ro)
size_t min_size; // smallest allocation block size
// (init under mu, then ro)
PagesAllocator *allocator;
};
// The default arena, which is used when 0 is passed instead of an Arena
// pointer.
static struct LowLevelAlloc::Arena default_arena;
// Non-malloc-hooked arenas: used only to allocate metadata for arenas that
// do not want malloc hook reporting, so that for them there's no malloc hook
// reporting even during arena creation.
static struct LowLevelAlloc::Arena unhooked_arena;
static struct LowLevelAlloc::Arena unhooked_async_sig_safe_arena;
namespace {
class DefaultPagesAllocator : public LowLevelAlloc::PagesAllocator {
public:
virtual ~DefaultPagesAllocator() {};
virtual void *MapPages(int32 flags, size_t size);
virtual void UnMapPages(int32 flags, void *addr, size_t size);
};
}
// magic numbers to identify allocated and unallocated blocks
static const intptr_t kMagicAllocated = 0x4c833e95;
static const intptr_t kMagicUnallocated = ~kMagicAllocated;
namespace {
class SCOPED_LOCKABLE ArenaLock {
public:
explicit ArenaLock(LowLevelAlloc::Arena *arena)
EXCLUSIVE_LOCK_FUNCTION(arena->mu)
: left_(false), mask_valid_(false), arena_(arena) {
if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
// We've decided not to support async-signal-safe arena use until
// there a demonstrated need. Here's how one could do it though
// (would need to be made more portable).
#if 0
sigset_t all;
sigfillset(&all);
this->mask_valid_ =
(pthread_sigmask(SIG_BLOCK, &all, &this->mask_) == 0);
#else
RAW_CHECK(false, "We do not yet support async-signal-safe arena.");
#endif
}
this->arena_->mu.Lock();
}
~ArenaLock() { RAW_CHECK(this->left_, "haven't left Arena region"); }
void Leave() UNLOCK_FUNCTION() {
this->arena_->mu.Unlock();
#if 0
if (this->mask_valid_) {
pthread_sigmask(SIG_SETMASK, &this->mask_, 0);
}
#endif
this->left_ = true;
}
private:
bool left_; // whether left region
bool mask_valid_;
#if 0
sigset_t mask_; // old mask of blocked signals
#endif
LowLevelAlloc::Arena *arena_;
DISALLOW_COPY_AND_ASSIGN(ArenaLock);
};
} // anonymous namespace
// create an appropriate magic number for an object at "ptr"
// "magic" should be kMagicAllocated or kMagicUnallocated
inline static intptr_t Magic(intptr_t magic, AllocList::Header *ptr) {
return magic ^ reinterpret_cast<intptr_t>(ptr);
}
// Initialize the fields of an Arena
static void ArenaInit(LowLevelAlloc::Arena *arena) {
if (arena->pagesize == 0) {
arena->pagesize = getpagesize();
// Round up block sizes to a power of two close to the header size.
arena->roundup = 16;
while (arena->roundup < sizeof (arena->freelist.header)) {
arena->roundup += arena->roundup;
}
// Don't allocate blocks less than twice the roundup size to avoid tiny
// free blocks.
arena->min_size = 2 * arena->roundup;
arena->freelist.header.size = 0;
arena->freelist.header.magic =
Magic(kMagicUnallocated, &arena->freelist.header);
arena->freelist.header.arena = arena;
arena->freelist.levels = 0;
memset(arena->freelist.next, 0, sizeof (arena->freelist.next));
arena->allocation_count = 0;
if (arena == &default_arena) {
// Default arena should be hooked, e.g. for heap-checker to trace
// pointer chains through objects in the default arena.
arena->flags = LowLevelAlloc::kCallMallocHook;
} else if (arena == &unhooked_async_sig_safe_arena) {
arena->flags = LowLevelAlloc::kAsyncSignalSafe;
} else {
arena->flags = 0; // other arenas' flags may be overridden by client,
// but unhooked_arena will have 0 in 'flags'.
}
arena->allocator = LowLevelAlloc::GetDefaultPagesAllocator();
}
}
// L < meta_data_arena->mu
LowLevelAlloc::Arena *LowLevelAlloc::NewArena(int32 flags,
Arena *meta_data_arena) {
return NewArenaWithCustomAlloc(flags, meta_data_arena, NULL);
}
// L < meta_data_arena->mu
LowLevelAlloc::Arena *LowLevelAlloc::NewArenaWithCustomAlloc(int32 flags,
Arena *meta_data_arena,
PagesAllocator *allocator) {
RAW_CHECK(meta_data_arena != 0, "must pass a valid arena");
if (meta_data_arena == &default_arena) {
if ((flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
meta_data_arena = &unhooked_async_sig_safe_arena;
} else if ((flags & LowLevelAlloc::kCallMallocHook) == 0) {
meta_data_arena = &unhooked_arena;
}
}
// Arena(0) uses the constructor for non-static contexts
Arena *result =
new (AllocWithArena(sizeof (*result), meta_data_arena)) Arena(0);
ArenaInit(result);
result->flags = flags;
if (allocator) {
result->allocator = allocator;
}
return result;
}
// L < arena->mu, L < arena->arena->mu
bool LowLevelAlloc::DeleteArena(Arena *arena) {
RAW_CHECK(arena != 0 && arena != &default_arena && arena != &unhooked_arena,
"may not delete default arena");
ArenaLock section(arena);
bool empty = (arena->allocation_count == 0);
section.Leave();
if (empty) {
while (arena->freelist.next[0] != 0) {
AllocList *region = arena->freelist.next[0];
size_t size = region->header.size;
arena->freelist.next[0] = region->next[0];
RAW_CHECK(region->header.magic ==
Magic(kMagicUnallocated, &region->header),
"bad magic number in DeleteArena()");
RAW_CHECK(region->header.arena == arena,
"bad arena pointer in DeleteArena()");
RAW_CHECK(size % arena->pagesize == 0,
"empty arena has non-page-aligned block size");
RAW_CHECK(reinterpret_cast<intptr_t>(region) % arena->pagesize == 0,
"empty arena has non-page-aligned block");
int munmap_result;
if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
munmap_result = munmap(region, size);
} else {
munmap_result = MallocHook::UnhookedMUnmap(region, size);
}
RAW_CHECK(munmap_result == 0,
"LowLevelAlloc::DeleteArena: munmap failed address");
}
Free(arena);
}
return empty;
}
// ---------------------------------------------------------------------------
// Return value rounded up to next multiple of align.
// align must be a power of two.
static intptr_t RoundUp(intptr_t addr, intptr_t align) {
return (addr + align - 1) & ~(align - 1);
}
// Equivalent to "return prev->next[i]" but with sanity checking
// that the freelist is in the correct order, that it
// consists of regions marked "unallocated", and that no two regions
// are adjacent in memory (they should have been coalesced).
// L < arena->mu
static AllocList *Next(int i, AllocList *prev, LowLevelAlloc::Arena *arena) {
RAW_CHECK(i < prev->levels, "too few levels in Next()");
AllocList *next = prev->next[i];
if (next != 0) {
RAW_CHECK(next->header.magic == Magic(kMagicUnallocated, &next->header),
"bad magic number in Next()");
RAW_CHECK(next->header.arena == arena,
"bad arena pointer in Next()");
if (prev != &arena->freelist) {
RAW_CHECK(prev < next, "unordered freelist");
RAW_CHECK(reinterpret_cast<char *>(prev) + prev->header.size <
reinterpret_cast<char *>(next), "malformed freelist");
}
}
return next;
}
// Coalesce list item "a" with its successor if they are adjacent.
static void Coalesce(AllocList *a) {
AllocList *n = a->next[0];
if (n != 0 && reinterpret_cast<char *>(a) + a->header.size ==
reinterpret_cast<char *>(n)) {
LowLevelAlloc::Arena *arena = a->header.arena;
a->header.size += n->header.size;
n->header.magic = 0;
n->header.arena = 0;
AllocList *prev[kMaxLevel];
LLA_SkiplistDelete(&arena->freelist, n, prev);
LLA_SkiplistDelete(&arena->freelist, a, prev);
a->levels = LLA_SkiplistLevels(a->header.size, arena->min_size, true);
LLA_SkiplistInsert(&arena->freelist, a, prev);
}
}
// Adds block at location "v" to the free list
// L >= arena->mu
static void AddToFreelist(void *v, LowLevelAlloc::Arena *arena) {
AllocList *f = reinterpret_cast<AllocList *>(
reinterpret_cast<char *>(v) - sizeof (f->header));
RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header),
"bad magic number in AddToFreelist()");
RAW_CHECK(f->header.arena == arena,
"bad arena pointer in AddToFreelist()");
f->levels = LLA_SkiplistLevels(f->header.size, arena->min_size, true);
AllocList *prev[kMaxLevel];
LLA_SkiplistInsert(&arena->freelist, f, prev);
f->header.magic = Magic(kMagicUnallocated, &f->header);
Coalesce(f); // maybe coalesce with successor
Coalesce(prev[0]); // maybe coalesce with predecessor
}
// Frees storage allocated by LowLevelAlloc::Alloc().
// L < arena->mu
void LowLevelAlloc::Free(void *v) {
if (v != 0) {
AllocList *f = reinterpret_cast<AllocList *>(
reinterpret_cast<char *>(v) - sizeof (f->header));
RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header),
"bad magic number in Free()");
LowLevelAlloc::Arena *arena = f->header.arena;
if ((arena->flags & kCallMallocHook) != 0) {
MallocHook::InvokeDeleteHook(v);
}
ArenaLock section(arena);
AddToFreelist(v, arena);
RAW_CHECK(arena->allocation_count > 0, "nothing in arena to free");
arena->allocation_count--;
section.Leave();
}
}
// allocates and returns a block of size bytes, to be freed with Free()
// L < arena->mu
static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
void *result = 0;
if (request != 0) {
AllocList *s; // will point to region that satisfies request
ArenaLock section(arena);
ArenaInit(arena);
// round up with header
size_t req_rnd = RoundUp(request + sizeof (s->header), arena->roundup);
for (;;) { // loop until we find a suitable region
// find the minimum levels that a block of this size must have
int i = LLA_SkiplistLevels(req_rnd, arena->min_size, false) - 1;
if (i < arena->freelist.levels) { // potential blocks exist
AllocList *before = &arena->freelist; // predecessor of s
while ((s = Next(i, before, arena)) != 0 && s->header.size < req_rnd) {
before = s;
}
if (s != 0) { // we found a region
break;
}
}
// we unlock before mmap() both because mmap() may call a callback hook,
// and because it may be slow.
arena->mu.Unlock();
// mmap generous 64K chunks to decrease
// the chances/impact of fragmentation:
size_t new_pages_size = RoundUp(req_rnd, arena->pagesize * 16);
void *new_pages = arena->allocator->MapPages(arena->flags, new_pages_size);
arena->mu.Lock();
s = reinterpret_cast<AllocList *>(new_pages);
s->header.size = new_pages_size;
// Pretend the block is allocated; call AddToFreelist() to free it.
s->header.magic = Magic(kMagicAllocated, &s->header);
s->header.arena = arena;
AddToFreelist(&s->levels, arena); // insert new region into free list
}
AllocList *prev[kMaxLevel];
LLA_SkiplistDelete(&arena->freelist, s, prev); // remove from free list
// s points to the first free region that's big enough
if (req_rnd + arena->min_size <= s->header.size) { // big enough to split
AllocList *n = reinterpret_cast<AllocList *>
(req_rnd + reinterpret_cast<char *>(s));
n->header.size = s->header.size - req_rnd;
n->header.magic = Magic(kMagicAllocated, &n->header);
n->header.arena = arena;
s->header.size = req_rnd;
AddToFreelist(&n->levels, arena);
}
s->header.magic = Magic(kMagicAllocated, &s->header);
RAW_CHECK(s->header.arena == arena, "");
arena->allocation_count++;
section.Leave();
result = &s->levels;
}
ANNOTATE_NEW_MEMORY(result, request);
return result;
}
void *LowLevelAlloc::Alloc(size_t request) {
void *result = DoAllocWithArena(request, &default_arena);
if ((default_arena.flags & kCallMallocHook) != 0) {
// this call must be directly in the user-called allocator function
// for MallocHook::GetCallerStackTrace to work properly
MallocHook::InvokeNewHook(result, request);
}
return result;
}
void *LowLevelAlloc::AllocWithArena(size_t request, Arena *arena) {
RAW_CHECK(arena != 0, "must pass a valid arena");
void *result = DoAllocWithArena(request, arena);
if ((arena->flags & kCallMallocHook) != 0) {
// this call must be directly in the user-called allocator function
// for MallocHook::GetCallerStackTrace to work properly
MallocHook::InvokeNewHook(result, request);
}
return result;
}
LowLevelAlloc::Arena *LowLevelAlloc::DefaultArena() {
return &default_arena;
}
static DefaultPagesAllocator *default_pages_allocator;
static union {
char chars[sizeof(DefaultPagesAllocator)];
void *ptr;
} debug_pages_allocator_space;
LowLevelAlloc::PagesAllocator *LowLevelAlloc::GetDefaultPagesAllocator(void) {
if (default_pages_allocator) {
return default_pages_allocator;
}
default_pages_allocator = new (debug_pages_allocator_space.chars) DefaultPagesAllocator();
return default_pages_allocator;
}
void *DefaultPagesAllocator::MapPages(int32 flags, size_t size) {
void *new_pages;
if ((flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
new_pages = MallocHook::UnhookedMMap(0, size,
PROT_WRITE|PROT_READ,
MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
} else {
new_pages = mmap(0, size,
PROT_WRITE|PROT_READ,
MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
}
RAW_CHECK(new_pages != MAP_FAILED, "mmap error");
return new_pages;
}
void DefaultPagesAllocator::UnMapPages(int32 flags, void *region, size_t size) {
int munmap_result;
if ((flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
munmap_result = munmap(region, size);
} else {
munmap_result = MallocHook::UnhookedMUnmap(region, size);
}
RAW_CHECK(munmap_result == 0,
"LowLevelAlloc::DeleteArena: munmap failed address");
}