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Diffstat (limited to 'absl/base/internal/low_level_alloc.cc')
| -rw-r--r-- | absl/base/internal/low_level_alloc.cc | 598 |
1 files changed, 598 insertions, 0 deletions
diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc new file mode 100644 index 000000000000..c55201b38bad --- /dev/null +++ b/absl/base/internal/low_level_alloc.cc @@ -0,0 +1,598 @@ +// Copyright 2017 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +// 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 "absl/base/config.h" + +#include "absl/base/internal/low_level_alloc.h" + +// LowLevelAlloc requires that the platform support low-level +// allocation of virtual memory. Platforms lacking this cannot use +// LowLevelAlloc. +#ifndef ABSL_LOW_LEVEL_ALLOC_MISSING + +#ifndef _WIN32 +#include <pthread.h> +#include <signal.h> +#include <sys/mman.h> +#include <unistd.h> +#else +#include <windows.h> +#endif + +#include <string.h> +#include <algorithm> +#include <atomic> +#include <cstddef> +#include <cerrno> +#include <new> // for placement-new + +#include "absl/base/dynamic_annotations.h" +#include "absl/base/internal/malloc_hook.h" +#include "absl/base/internal/malloc_hook_invoke.h" +#include "absl/base/internal/raw_logging.h" +#include "absl/base/internal/spinlock.h" + +// MAP_ANONYMOUS +#if defined(__APPLE__) +// For mmap, Linux defines both MAP_ANONYMOUS and MAP_ANON and says MAP_ANON is +// deprecated. In Darwin, MAP_ANON is all there is. +#if !defined MAP_ANONYMOUS +#define MAP_ANONYMOUS MAP_ANON +#endif // !MAP_ANONYMOUS +#endif // __APPLE__ + +namespace absl { +namespace base_internal { + +// A first-fit allocator with amortized logarithmic free() time. + +// --------------------------------------------------------------------------- +static const int kMaxLevel = 30; + +namespace { +// This struct describes one allocated block, or one free block. +struct AllocList { + struct Header { + // Size of entire region, including this field. Must be + // first. Valid in both allocated and unallocated blocks. + uintptr_t size; + + // kMagicAllocated or kMagicUnallocated xor this. + uintptr_t magic; + + // Pointer to parent arena. + LowLevelAlloc::Arena *arena; + + // Aligns regions to 0 mod 2*sizeof(void*). + void *dummy_for_alignment; + } header; + + // Next two fields: in unallocated blocks: freelist skiplist data + // in allocated blocks: overlaps with client data + + // Levels in skiplist used. + int levels; + + // Actually has levels elements. The AllocList node may not have room + // for all kMaxLevel entries. See max_fit in LLA_SkiplistLevels(). + AllocList *next[kMaxLevel]; +}; +} // namespace + +// --------------------------------------------------------------------------- +// 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(uint32_t *state) { + uint32_t r = *state; + int result = 1; + while ((((r = r*1103515245 + 12345) >> 30) & 1) == 0) { + result++; + } + *state = r; + 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, uint32_t *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. + size_t max_fit = (size - offsetof(AllocList, next)) / sizeof(AllocList *); + int level = IntLog2(size, base) + (random != nullptr ? Random(random) : 1); + if (static_cast<size_t>(level) > max_fit) level = static_cast<int>(max_fit); + if (level > kMaxLevel-1) level = kMaxLevel - 1; + ABSL_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]) != nullptr && n < e; p = n) { + } + prev[level] = p; + } + return (head->levels == 0) ? nullptr : 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); + ABSL_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] == nullptr) { + head->levels--; // reduce head->levels if level unused + } +} + +// --------------------------------------------------------------------------- +// Arena implementation + +struct LowLevelAlloc::Arena { + // This constructor does nothing, and relies on zero-initialization to get + // the proper initial state. + Arena() : mu(base_internal::kLinkerInitialized) {} // NOLINT + explicit Arena(int) // NOLINT(readability/casting) + : // Avoid recursive cooperative scheduling w/ kernel scheduling. + mu(base_internal::SCHEDULE_KERNEL_ONLY), + // Set pagesize to zero explicitly for non-static init. + pagesize(0), + random(0) {} + + base_internal::SpinLock mu; // protects freelist, allocation_count, + // pagesize, roundup, min_size + AllocList freelist; // head of free list; sorted by addr (under mu) + int32_t allocation_count; // count of allocated blocks (under mu) + std::atomic<uint32_t> flags; // flags passed to NewArena (ro after init) + size_t pagesize; // ==getpagesize() (init under mu, then ro) + size_t roundup; // lowest 2^n >= max(16,sizeof (AllocList)) + // (init under mu, then ro) + size_t min_size; // smallest allocation block size + // (init under mu, then ro) + uint32_t random; // PRNG state +}; + +// The default arena, which is used when 0 is passed instead of an Arena +// pointer. +static struct LowLevelAlloc::Arena default_arena; // NOLINT + +// 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; // NOLINT + +#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING +static struct LowLevelAlloc::Arena unhooked_async_sig_safe_arena; // NOLINT +#endif + +// magic numbers to identify allocated and unallocated blocks +static const uintptr_t kMagicAllocated = 0x4c833e95U; +static const uintptr_t kMagicUnallocated = ~kMagicAllocated; + +namespace { +class SCOPED_LOCKABLE ArenaLock { + public: + explicit ArenaLock(LowLevelAlloc::Arena *arena) + EXCLUSIVE_LOCK_FUNCTION(arena->mu) + : arena_(arena) { +#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING + if (arena == &unhooked_async_sig_safe_arena || + (arena->flags.load(std::memory_order_relaxed) & + LowLevelAlloc::kAsyncSignalSafe) != 0) { + sigset_t all; + sigfillset(&all); + mask_valid_ = pthread_sigmask(SIG_BLOCK, &all, &mask_) == 0; + } +#endif + arena_->mu.Lock(); + } + ~ArenaLock() { ABSL_RAW_CHECK(left_, "haven't left Arena region"); } + void Leave() UNLOCK_FUNCTION() { + arena_->mu.Unlock(); +#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING + if (mask_valid_) { + pthread_sigmask(SIG_SETMASK, &mask_, nullptr); + } +#endif + left_ = true; + } + + private: + bool left_ = false; // whether left region +#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING + bool mask_valid_ = false; + sigset_t mask_; // old mask of blocked signals +#endif + LowLevelAlloc::Arena *arena_; + ArenaLock(const ArenaLock &) = delete; + ArenaLock &operator=(const ArenaLock &) = delete; +}; +} // namespace + +// create an appropriate magic number for an object at "ptr" +// "magic" should be kMagicAllocated or kMagicUnallocated +inline static uintptr_t Magic(uintptr_t magic, AllocList::Header *ptr) { + return magic ^ reinterpret_cast<uintptr_t>(ptr); +} + +// Initialize the fields of an Arena +static void ArenaInit(LowLevelAlloc::Arena *arena) { + if (arena->pagesize == 0) { +#ifdef _WIN32 + SYSTEM_INFO system_info; + GetSystemInfo(&system_info); + arena->pagesize = std::max(system_info.dwPageSize, + system_info.dwAllocationGranularity); +#else + arena->pagesize = getpagesize(); +#endif + // 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.store(LowLevelAlloc::kCallMallocHook, + std::memory_order_relaxed); + } +#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING + else if (arena == // NOLINT(readability/braces) + &unhooked_async_sig_safe_arena) { + arena->flags.store(LowLevelAlloc::kAsyncSignalSafe, + std::memory_order_relaxed); + } +#endif + else { // NOLINT(readability/braces) + // other arenas' flags may be overridden by client, + // but unhooked_arena will have 0 in 'flags'. + arena->flags.store(0, std::memory_order_relaxed); + } + } +} + +// L < meta_data_arena->mu +LowLevelAlloc::Arena *LowLevelAlloc::NewArena(int32_t flags, + Arena *meta_data_arena) { + ABSL_RAW_CHECK(meta_data_arena != nullptr, "must pass a valid arena"); + if (meta_data_arena == &default_arena) { +#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING + if ((flags & LowLevelAlloc::kAsyncSignalSafe) != 0) { + meta_data_arena = &unhooked_async_sig_safe_arena; + } else // NOLINT(readability/braces) +#endif + 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.store(flags, std::memory_order_relaxed); + return result; +} + +// L < arena->mu, L < arena->arena->mu +bool LowLevelAlloc::DeleteArena(Arena *arena) { + ABSL_RAW_CHECK( + arena != nullptr && 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] != nullptr) { + AllocList *region = arena->freelist.next[0]; + size_t size = region->header.size; + arena->freelist.next[0] = region->next[0]; + ABSL_RAW_CHECK( + region->header.magic == Magic(kMagicUnallocated, ®ion->header), + "bad magic number in DeleteArena()"); + ABSL_RAW_CHECK(region->header.arena == arena, + "bad arena pointer in DeleteArena()"); + ABSL_RAW_CHECK(size % arena->pagesize == 0, + "empty arena has non-page-aligned block size"); + ABSL_RAW_CHECK(reinterpret_cast<uintptr_t>(region) % arena->pagesize == 0, + "empty arena has non-page-aligned block"); + int munmap_result; +#ifdef _WIN32 + munmap_result = VirtualFree(region, 0, MEM_RELEASE); + ABSL_RAW_CHECK(munmap_result != 0, + "LowLevelAlloc::DeleteArena: VitualFree failed"); +#else + if ((arena->flags.load(std::memory_order_relaxed) & + LowLevelAlloc::kAsyncSignalSafe) == 0) { + munmap_result = munmap(region, size); + } else { + munmap_result = MallocHook::UnhookedMUnmap(region, size); + } + if (munmap_result != 0) { + ABSL_RAW_LOG(FATAL, "LowLevelAlloc::DeleteArena: munmap failed: %d", + errno); + } +#endif + } + Free(arena); + } + return empty; +} + +// --------------------------------------------------------------------------- + +// Addition, checking for overflow. The intent is to die if an external client +// manages to push through a request that would cause arithmetic to fail. +static inline uintptr_t CheckedAdd(uintptr_t a, uintptr_t b) { + uintptr_t sum = a + b; + ABSL_RAW_CHECK(sum >= a, "LowLevelAlloc arithmetic overflow"); + return sum; +} + +// Return value rounded up to next multiple of align. +// align must be a power of two. +static inline uintptr_t RoundUp(uintptr_t addr, uintptr_t align) { + return CheckedAdd(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) { + ABSL_RAW_CHECK(i < prev->levels, "too few levels in Next()"); + AllocList *next = prev->next[i]; + if (next != nullptr) { + ABSL_RAW_CHECK( + next->header.magic == Magic(kMagicUnallocated, &next->header), + "bad magic number in Next()"); + ABSL_RAW_CHECK(next->header.arena == arena, "bad arena pointer in Next()"); + if (prev != &arena->freelist) { + ABSL_RAW_CHECK(prev < next, "unordered freelist"); + ABSL_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 != nullptr && 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 = nullptr; + 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, + &arena->random); + 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)); + ABSL_RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header), + "bad magic number in AddToFreelist()"); + ABSL_RAW_CHECK(f->header.arena == arena, + "bad arena pointer in AddToFreelist()"); + f->levels = LLA_SkiplistLevels(f->header.size, arena->min_size, + &arena->random); + 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 != nullptr) { + AllocList *f = reinterpret_cast<AllocList *>( + reinterpret_cast<char *>(v) - sizeof (f->header)); + ABSL_RAW_CHECK(f->header.magic == Magic(kMagicAllocated, &f->header), + "bad magic number in Free()"); + LowLevelAlloc::Arena *arena = f->header.arena; + if ((arena->flags.load(std::memory_order_relaxed) & kCallMallocHook) != 0) { + MallocHook::InvokeDeleteHook(v); + } + ArenaLock section(arena); + AddToFreelist(v, arena); + ABSL_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 = nullptr; + 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(CheckedAdd(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, nullptr) - 1; + if (i < arena->freelist.levels) { // potential blocks exist + AllocList *before = &arena->freelist; // predecessor of s + while ((s = Next(i, before, arena)) != nullptr && + s->header.size < req_rnd) { + before = s; + } + if (s != nullptr) { // 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; +#ifdef _WIN32 + new_pages = VirtualAlloc(0, new_pages_size, + MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE); + ABSL_RAW_CHECK(new_pages != nullptr, "VirtualAlloc failed"); +#else + if ((arena->flags.load(std::memory_order_relaxed) & + LowLevelAlloc::kAsyncSignalSafe) != 0) { + new_pages = MallocHook::UnhookedMMap(nullptr, new_pages_size, + PROT_WRITE|PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); + } else { + new_pages = mmap(nullptr, new_pages_size, PROT_WRITE | PROT_READ, + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); + } + if (new_pages == MAP_FAILED) { + ABSL_RAW_LOG(FATAL, "mmap error: %d", errno); + } +#endif + 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 (CheckedAdd(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); + ABSL_RAW_CHECK(s->header.arena == arena, ""); + arena->allocation_count++; + section.Leave(); + result = &s->levels; + } + ANNOTATE_MEMORY_IS_UNINITIALIZED(result, request); + return result; +} + +void *LowLevelAlloc::Alloc(size_t request) { + void *result = DoAllocWithArena(request, &default_arena); + if ((default_arena.flags.load(std::memory_order_relaxed) & + 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) { + ABSL_RAW_CHECK(arena != nullptr, "must pass a valid arena"); + void *result = DoAllocWithArena(request, arena); + if ((arena->flags.load(std::memory_order_relaxed) & 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; +} + +} // namespace base_internal +} // namespace absl + +#endif // ABSL_LOW_LEVEL_ALLOC_MISSING |