src/jsapi-tests/testGCAllocator.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include <cstdlib>

#include "gc/Memory.h"
#include "jsapi-tests/tests.h"

#if defined(XP_WIN)
#  include "util/WindowsWrapper.h"
#  include <psapi.h>
#elif defined(__wasi__)
// Nothing.
#else
#  include <algorithm>
#  include <errno.h>
#  include <sys/mman.h>
#  include <sys/resource.h>
#  include <sys/stat.h>
#  include <sys/types.h>
#  include <unistd.h>
#endif

BEGIN_TEST(testGCAllocator) {
#ifdef JS_64BIT
  // If we're using the scattershot allocator, this test does not apply.
  if (js::gc::UsingScattershotAllocator()) {
    return true;
  }
#endif

  size_t PageSize = js::gc::SystemPageSize();

  /* Finish any ongoing background free activity. */
  js::gc::FinishGC(cx);

  bool growUp = false;
  CHECK(addressesGrowUp(&growUp));

  if (growUp) {
    return testGCAllocatorUp(PageSize);
  } else {
    return testGCAllocatorDown(PageSize);
  }
}

static const size_t Chunk = 512 * 1024;
static const size_t Alignment = 2 * Chunk;
static const int MaxTempChunks = 4096;
static const size_t StagingSize = 16 * Chunk;

bool addressesGrowUp(bool* resultOut) {
  /*
   * Try to detect whether the OS allocates memory in increasing or decreasing
   * address order by making several allocations and comparing the addresses.
   */

  static const unsigned ChunksToTest = 20;
  static const int ThresholdCount = 15;

  void* chunks[ChunksToTest];
  for (unsigned i = 0; i < ChunksToTest; i++) {
    chunks[i] = mapMemory(2 * Chunk);
    CHECK(chunks[i]);
  }

  int upCount = 0;
  int downCount = 0;

  for (unsigned i = 0; i < ChunksToTest - 1; i++) {
    if (chunks[i] < chunks[i + 1]) {
      upCount++;
    } else {
      downCount++;
    }
  }

  for (unsigned i = 0; i < ChunksToTest; i++) {
    unmapPages(chunks[i], 2 * Chunk);
  }

  /* Check results were mostly consistent. */
  CHECK(abs(upCount - downCount) >= ThresholdCount);

  *resultOut = upCount > downCount;

  return true;
}

size_t offsetFromAligned(void* p) { return uintptr_t(p) % Alignment; }

enum AllocType { UseNormalAllocator, UseLastDitchAllocator };

bool testGCAllocatorUp(const size_t PageSize) {
  const size_t UnalignedSize = StagingSize + Alignment - PageSize;
  void* chunkPool[MaxTempChunks];
  // Allocate a contiguous chunk that we can partition for testing.
  void* stagingArea = mapMemory(UnalignedSize);
  if (!stagingArea) {
    return false;
  }
  // Ensure that the staging area is aligned.
  unmapPages(stagingArea, UnalignedSize);
  if (offsetFromAligned(stagingArea)) {
    const size_t Offset = offsetFromAligned(stagingArea);
    // Place the area at the lowest aligned address.
    stagingArea = (void*)(uintptr_t(stagingArea) + (Alignment - Offset));
  }
  mapMemoryAt(stagingArea, StagingSize);
  // Make sure there are no available chunks below the staging area.
  int tempChunks;
  if (!fillSpaceBeforeStagingArea(tempChunks, stagingArea, chunkPool, false)) {
    return false;
  }
  // Unmap the staging area so we can set it up for testing.
  unmapPages(stagingArea, StagingSize);
  // Check that the first chunk is used if it is aligned.
  CHECK(positionIsCorrect("xxooxxx---------", stagingArea, chunkPool,
                          tempChunks));
  // Check that the first chunk is used if it can be aligned.
  CHECK(positionIsCorrect("x-ooxxx---------", stagingArea, chunkPool,
                          tempChunks));
  // Check that an aligned chunk after a single unalignable chunk is used.
  CHECK(positionIsCorrect("x--xooxxx-------", stagingArea, chunkPool,
                          tempChunks));
  // Check that we fall back to the slow path after two unalignable chunks.
  CHECK(positionIsCorrect("x--xx--xoo--xxx-", stagingArea, chunkPool,
                          tempChunks));
  // Check that we also fall back after an unalignable and an alignable chunk.
  CHECK(positionIsCorrect("x--xx---x-oo--x-", stagingArea, chunkPool,
                          tempChunks));
  // Check that the last ditch allocator works as expected.
  CHECK(positionIsCorrect("x--xx--xx-oox---", stagingArea, chunkPool,
                          tempChunks, UseLastDitchAllocator));
  // Check that the last ditch allocator can deal with naturally aligned chunks.
  CHECK(positionIsCorrect("x--xx--xoo------", stagingArea, chunkPool,
                          tempChunks, UseLastDitchAllocator));

  // Clean up.
  while (--tempChunks >= 0) {
    unmapPages(chunkPool[tempChunks], 2 * Chunk);
  }
  return true;
}

bool testGCAllocatorDown(const size_t PageSize) {
  const size_t UnalignedSize = StagingSize + Alignment - PageSize;
  void* chunkPool[MaxTempChunks];
  // Allocate a contiguous chunk that we can partition for testing.
  void* stagingArea = mapMemory(UnalignedSize);
  if (!stagingArea) {
    return false;
  }
  // Ensure that the staging area is aligned.
  unmapPages(stagingArea, UnalignedSize);
  if (offsetFromAligned(stagingArea)) {
    void* stagingEnd = (void*)(uintptr_t(stagingArea) + UnalignedSize);
    const size_t Offset = offsetFromAligned(stagingEnd);
    // Place the area at the highest aligned address.
    stagingArea = (void*)(uintptr_t(stagingEnd) - Offset - StagingSize);
  }
  mapMemoryAt(stagingArea, StagingSize);
  // Make sure there are no available chunks above the staging area.
  int tempChunks;
  if (!fillSpaceBeforeStagingArea(tempChunks, stagingArea, chunkPool, true)) {
    return false;
  }
  // Unmap the staging area so we can set it up for testing.
  unmapPages(stagingArea, StagingSize);
  // Check that the first chunk is used if it is aligned.
  CHECK(positionIsCorrect("---------xxxooxx", stagingArea, chunkPool,
                          tempChunks));
  // Check that the first chunk is used if it can be aligned.
  CHECK(positionIsCorrect("---------xxxoo-x", stagingArea, chunkPool,
                          tempChunks));
  // Check that an aligned chunk after a single unalignable chunk is used.
  CHECK(positionIsCorrect("-------xxxoox--x", stagingArea, chunkPool,
                          tempChunks));
  // Check that we fall back to the slow path after two unalignable chunks.
  CHECK(positionIsCorrect("-xxx--oox--xx--x", stagingArea, chunkPool,
                          tempChunks));
  // Check that we also fall back after an unalignable and an alignable chunk.
  CHECK(positionIsCorrect("-x--oo-x---xx--x", stagingArea, chunkPool,
                          tempChunks));
  // Check that the last ditch allocator works as expected.
  CHECK(positionIsCorrect("---xoo-xx--xx--x", stagingArea, chunkPool,
                          tempChunks, UseLastDitchAllocator));
  // Check that the last ditch allocator can deal with naturally aligned chunks.
  CHECK(positionIsCorrect("------oox--xx--x", stagingArea, chunkPool,
                          tempChunks, UseLastDitchAllocator));

  // Clean up.
  while (--tempChunks >= 0) {
    unmapPages(chunkPool[tempChunks], 2 * Chunk);
  }
  return true;
}

bool fillSpaceBeforeStagingArea(int& tempChunks, void* stagingArea,
                                void** chunkPool, bool addressesGrowDown) {
  // Make sure there are no available chunks before the staging area.
  tempChunks = 0;
  chunkPool[tempChunks++] = mapMemory(2 * Chunk);
  while (tempChunks < MaxTempChunks && chunkPool[tempChunks - 1] &&
         (chunkPool[tempChunks - 1] < stagingArea) ^ addressesGrowDown) {
    chunkPool[tempChunks++] = mapMemory(2 * Chunk);
    if (!chunkPool[tempChunks - 1]) {
      break;  // We already have our staging area, so OOM here is okay.
    }
    if ((chunkPool[tempChunks - 1] < chunkPool[tempChunks - 2]) ^
        addressesGrowDown) {
      break;  // The address growth direction is inconsistent!
    }
  }
  // OOM also means success in this case.
  if (!chunkPool[tempChunks - 1]) {
    --tempChunks;
    return true;
  }
  // Bail if we can't guarantee the right address space layout.
  if ((chunkPool[tempChunks - 1] < stagingArea) ^ addressesGrowDown ||
      (tempChunks > 1 &&
       (chunkPool[tempChunks - 1] < chunkPool[tempChunks - 2]) ^
           addressesGrowDown)) {
    while (--tempChunks >= 0) {
      unmapPages(chunkPool[tempChunks], 2 * Chunk);
    }
    unmapPages(stagingArea, StagingSize);
    return false;
  }
  return true;
}

bool positionIsCorrect(const char* str, void* base, void** chunkPool,
                       int tempChunks,
                       AllocType allocator = UseNormalAllocator) {
  // str represents a region of memory, with each character representing a
  // region of Chunk bytes. str should contain only x, o and -, where
  // x = mapped by the test to set up the initial conditions,
  // o = mapped by the GC allocator, and
  // - = unmapped.
  // base should point to a region of contiguous free memory
  // large enough to hold strlen(str) chunks of Chunk bytes.
  int len = strlen(str);
  int i;
  // Find the index of the desired address.
  for (i = 0; i < len && str[i] != 'o'; ++i)
    ;
  void* desired = (void*)(uintptr_t(base) + i * Chunk);
  // Map the regions indicated by str.
  for (i = 0; i < len; ++i) {
    if (str[i] == 'x') {
      mapMemoryAt((void*)(uintptr_t(base) + i * Chunk), Chunk);
    }
  }
  // Allocate using the GC's allocator.
  void* result;
  if (allocator == UseNormalAllocator) {
    result = js::gc::MapAlignedPages(2 * Chunk, Alignment);
  } else {
    result = js::gc::TestMapAlignedPagesLastDitch(2 * Chunk, Alignment);
  }
  // Clean up the mapped regions.
  if (result) {
    js::gc::UnmapPages(result, 2 * Chunk);
  }
  for (--i; i >= 0; --i) {
    if (str[i] == 'x') {
      js::gc::UnmapPages((void*)(uintptr_t(base) + i * Chunk), Chunk);
    }
  }
  // CHECK returns, so clean up on failure.
  if (result != desired) {
    while (--tempChunks >= 0) {
      js::gc::UnmapPages(chunkPool[tempChunks], 2 * Chunk);
    }
  }
  return result == desired;
}

#if defined(XP_WIN)

void* mapMemoryAt(void* desired, size_t length) {
  return VirtualAlloc(desired, length, MEM_COMMIT | MEM_RESERVE,
                      PAGE_READWRITE);
}

void* mapMemory(size_t length) {
  return VirtualAlloc(nullptr, length, MEM_COMMIT | MEM_RESERVE,
                      PAGE_READWRITE);
}

void unmapPages(void* p, size_t size) {
  MOZ_ALWAYS_TRUE(VirtualFree(p, 0, MEM_RELEASE));
}

#elif defined(__wasi__)

void* mapMemoryAt(void* desired, size_t length) { return nullptr; }

void* mapMemory(size_t length) {
  void* addr = nullptr;
  if (int err = posix_memalign(&addr, js::gc::SystemPageSize(), length)) {
    MOZ_ASSERT(err == ENOMEM);
  }
  MOZ_ASSERT(addr);
  memset(addr, 0, length);
  return addr;
}

void unmapPages(void* p, size_t size) { free(p); }

#else

void* mapMemoryAt(void* desired, size_t length) {
  void* region = mmap(desired, length, PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANON, -1, 0);
  if (region == MAP_FAILED) {
    return nullptr;
  }
  if (region != desired) {
    if (munmap(region, length)) {
      MOZ_RELEASE_ASSERT(errno == ENOMEM);
    }
    return nullptr;
  }
  return region;
}

void* mapMemory(size_t length) {
  int prot = PROT_READ | PROT_WRITE;
  int flags = MAP_PRIVATE | MAP_ANON;
  int fd = -1;
  off_t offset = 0;
  void* region = mmap(nullptr, length, prot, flags, fd, offset);
  if (region == MAP_FAILED) {
    return nullptr;
  }
  return region;
}

void unmapPages(void* p, size_t size) {
  if (munmap(p, size)) {
    MOZ_RELEASE_ASSERT(errno == ENOMEM);
  }
}

#endif

END_TEST(testGCAllocator)