path: root/js/src/jit/ExecutableAllocator.cpp

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#include "jit/ExecutableAllocator.h"

#include "gc/Zone.h"
#include "js/MemoryMetrics.h"
#include "util/Poison.h"

using namespace js::jit;

ExecutablePool::~ExecutablePool() {
#ifdef DEBUG
  for (size_t bytes : m_codeBytes) {
    MOZ_ASSERT(bytes == 0);
  }
#endif

  MOZ_ASSERT(!isMarked());

  m_allocator->releasePoolPages(this);
}

void ExecutablePool::release(bool willDestroy) {
  MOZ_ASSERT(m_refCount != 0);
  MOZ_ASSERT_IF(willDestroy, m_refCount == 1);
  if (--m_refCount == 0) {
    js_delete(this);
  }
}

void ExecutablePool::release(size_t n, CodeKind kind) {
  m_codeBytes[kind] -= n;
  MOZ_ASSERT(m_codeBytes[kind] < m_allocation.size);  // Shouldn't underflow.

  release();
}

void ExecutablePool::addRef() {
  // It should be impossible for us to roll over, because only small
  // pools have multiple holders, and they have one holder per chunk
  // of generated code, and they only hold 16KB or so of code.
  MOZ_ASSERT(m_refCount);
  ++m_refCount;
  MOZ_ASSERT(m_refCount, "refcount overflow");
}

void* ExecutablePool::alloc(size_t n, CodeKind kind) {
  MOZ_ASSERT(n <= available());
  void* result = m_freePtr;
  m_freePtr += n;

  m_codeBytes[kind] += n;

  MOZ_MAKE_MEM_UNDEFINED(result, n);
  return result;
}

size_t ExecutablePool::available() const {
  MOZ_ASSERT(m_end >= m_freePtr);
  return m_end - m_freePtr;
}

ExecutableAllocator::~ExecutableAllocator() {
  for (size_t i = 0; i < m_smallPools.length(); i++) {
    m_smallPools[i]->release(/* willDestroy = */ true);
  }

  // If this asserts we have a pool leak.
  MOZ_ASSERT(m_pools.empty());
}

ExecutablePool* ExecutableAllocator::poolForSize(size_t n) {
  // Try to fit in an existing small allocator.  Use the pool with the
  // least available space that is big enough (best-fit).  This is the
  // best strategy because (a) it maximizes the chance of the next
  // allocation fitting in a small pool, and (b) it minimizes the
  // potential waste when a small pool is next abandoned.
  ExecutablePool* minPool = nullptr;
  for (size_t i = 0; i < m_smallPools.length(); i++) {
    ExecutablePool* pool = m_smallPools[i];
    if (n <= pool->available() &&
        (!minPool || pool->available() < minPool->available())) {
      minPool = pool;
    }
  }
  if (minPool) {
    minPool->addRef();
    return minPool;
  }

  // If the request is large, we just provide a unshared allocator
  if (n > ExecutableCodePageSize) {
    return createPool(n);
  }

  // Create a new allocator
  ExecutablePool* pool = createPool(ExecutableCodePageSize);
  if (!pool) {
    return nullptr;
  }
  // At this point, local |pool| is the owner.

  if (m_smallPools.length() < maxSmallPools) {
    // We haven't hit the maximum number of live pools; add the new pool.
    // If append() OOMs, we just return an unshared allocator.
    if (m_smallPools.append(pool)) {
      pool->addRef();
    }
  } else {
    // Find the pool with the least space.
    int iMin = 0;
    for (size_t i = 1; i < m_smallPools.length(); i++) {
      if (m_smallPools[i]->available() < m_smallPools[iMin]->available()) {
        iMin = i;
      }
    }

    // If the new allocator will result in more free space than the small
    // pool with the least space, then we will use it instead
    ExecutablePool* minPool = m_smallPools[iMin];
    if ((pool->available() - n) > minPool->available()) {
      minPool->release();
      m_smallPools[iMin] = pool;
      pool->addRef();
    }
  }

  // Pass ownership to the caller.
  return pool;
}

/* static */
size_t ExecutableAllocator::roundUpAllocationSize(size_t request,
                                                  size_t granularity) {
  if ((std::numeric_limits<size_t>::max() - granularity) <= request) {
    return OVERSIZE_ALLOCATION;
  }

  // Round up to next page boundary
  size_t size = request + (granularity - 1);
  size = size & ~(granularity - 1);
  MOZ_ASSERT(size >= request);
  return size;
}

ExecutablePool* ExecutableAllocator::createPool(size_t n) {
  size_t allocSize = roundUpAllocationSize(n, ExecutableCodePageSize);
  if (allocSize == OVERSIZE_ALLOCATION) {
    return nullptr;
  }

  ExecutablePool::Allocation a = systemAlloc(allocSize);
  if (!a.pages) {
    return nullptr;
  }

  ExecutablePool* pool = js_new<ExecutablePool>(this, a);
  if (!pool) {
    systemRelease(a);
    return nullptr;
  }

  if (!m_pools.put(pool)) {
    // Note: this will call |systemRelease(a)|.
    js_delete(pool);
    return nullptr;
  }

  return pool;
}

void* ExecutableAllocator::alloc(JSContext* cx, size_t n,
                                 ExecutablePool** poolp, CodeKind type) {
  // Caller must ensure 'n' is word-size aligned. If all allocations are
  // of word sized quantities, then all subsequent allocations will be
  // aligned.
  MOZ_ASSERT(roundUpAllocationSize(n, sizeof(void*)) == n);

  if (n == OVERSIZE_ALLOCATION) {
    *poolp = nullptr;
    return nullptr;
  }

  *poolp = poolForSize(n);
  if (!*poolp) {
    return nullptr;
  }

  // This alloc is infallible because poolForSize() just obtained
  // (found, or created if necessary) a pool that had enough space.
  void* result = (*poolp)->alloc(n, type);
  MOZ_ASSERT(result);

  return result;
}

void ExecutableAllocator::releasePoolPages(ExecutablePool* pool) {
  MOZ_ASSERT(pool->m_allocation.pages);
  systemRelease(pool->m_allocation);

  // Pool may not be present in m_pools if we hit OOM during creation.
  if (auto ptr = m_pools.lookup(pool)) {
    m_pools.remove(ptr);
  }
}

void ExecutableAllocator::purge() {
  for (size_t i = 0; i < m_smallPools.length();) {
    ExecutablePool* pool = m_smallPools[i];
    if (pool->m_refCount > 1) {
      // Releasing this pool is not going to deallocate it, so we might as
      // well hold on to it and reuse it for future allocations.
      i++;
      continue;
    }

    MOZ_ASSERT(pool->m_refCount == 1);
    pool->release();
    m_smallPools.erase(&m_smallPools[i]);
  }
}

void ExecutableAllocator::addSizeOfCode(JS::CodeSizes* sizes) const {
  for (ExecPoolHashSet::Range r = m_pools.all(); !r.empty(); r.popFront()) {
    ExecutablePool* pool = r.front();
    sizes->ion += pool->m_codeBytes[CodeKind::Ion];
    sizes->baseline += pool->m_codeBytes[CodeKind::Baseline];
    sizes->regexp += pool->m_codeBytes[CodeKind::RegExp];
    sizes->other += pool->m_codeBytes[CodeKind::Other];
    sizes->unused += pool->m_allocation.size - pool->usedCodeBytes();
  }
}

/* static */
void ExecutableAllocator::reprotectPool(JSRuntime* rt, ExecutablePool* pool,
                                        ProtectionSetting protection,
                                        MustFlushICache flushICache) {
  char* start = pool->m_allocation.pages;
  AutoEnterOOMUnsafeRegion oomUnsafe;
  if (!ReprotectRegion(start, pool->m_freePtr - start, protection,
                       flushICache)) {
    oomUnsafe.crash("ExecutableAllocator::reprotectPool");
  }
}

/* static */
void ExecutableAllocator::poisonCode(JSRuntime* rt,
                                     JitPoisonRangeVector& ranges) {
  MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));

#ifdef DEBUG
  // Make sure no pools have the mark bit set.
  for (size_t i = 0; i < ranges.length(); i++) {
    MOZ_ASSERT(!ranges[i].pool->isMarked());
  }
#endif

  for (size_t i = 0; i < ranges.length(); i++) {
    ExecutablePool* pool = ranges[i].pool;
    if (pool->m_refCount == 1) {
      // This is the last reference so the release() call below will
      // unmap the memory. Don't bother poisoning it.
      continue;
    }

    MOZ_ASSERT(pool->m_refCount > 1);

    // Use the pool's mark bit to indicate we made the pool writable.
    // This avoids reprotecting a pool multiple times.
    if (!pool->isMarked()) {
      reprotectPool(rt, pool, ProtectionSetting::Writable, MustFlushICache::No);
      pool->mark();
    }

    // Note: we use memset instead of js::Poison because we want to poison
    // JIT code in release builds too. Furthermore, we don't want the
    // invalid-ObjectValue poisoning js::Poison does in debug builds.
    memset(ranges[i].start, JS_SWEPT_CODE_PATTERN, ranges[i].size);
    MOZ_MAKE_MEM_NOACCESS(ranges[i].start, ranges[i].size);
  }

  // Make the pools executable again and drop references. We don't flush the
  // ICache here to not add extra overhead.
  for (size_t i = 0; i < ranges.length(); i++) {
    ExecutablePool* pool = ranges[i].pool;
    if (pool->isMarked()) {
      reprotectPool(rt, pool, ProtectionSetting::Executable,
                    MustFlushICache::No);
      pool->unmark();
    }
    pool->release();
  }
}

ExecutablePool::Allocation ExecutableAllocator::systemAlloc(size_t n) {
  void* allocation = AllocateExecutableMemory(n, ProtectionSetting::Executable,
                                              MemCheckKind::MakeNoAccess);
  ExecutablePool::Allocation alloc = {reinterpret_cast<char*>(allocation), n};
  return alloc;
}

void ExecutableAllocator::systemRelease(
    const ExecutablePool::Allocation& alloc) {
  DeallocateExecutableMemory(alloc.pages, alloc.size);
}