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// Copyright 2021 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/heap/code-range.h"
#include "src/base/bits.h"
#include "src/base/lazy-instance.h"
#include "src/base/once.h"
#include "src/codegen/constants-arch.h"
#include "src/common/globals.h"
#include "src/flags/flags.h"
#include "src/heap/heap-inl.h"
#include "src/utils/allocation.h"
#if defined(V8_OS_WIN64)
#include "src/diagnostics/unwinding-info-win64.h"
#endif // V8_OS_WIN64
namespace v8 {
namespace internal {
namespace {
DEFINE_LAZY_LEAKY_OBJECT_GETTER(CodeRangeAddressHint, GetCodeRangeAddressHint)
void FunctionInStaticBinaryForAddressHint() {}
} // anonymous namespace
Address CodeRangeAddressHint::GetAddressHint(size_t code_range_size,
size_t alignment) {
base::MutexGuard guard(&mutex_);
// Try to allocate code range in the preferred region where we can use
// short instructions for calling/jumping to embedded builtins.
base::AddressRegion preferred_region = Isolate::GetShortBuiltinsCallRegion();
Address result = 0;
auto it = recently_freed_.find(code_range_size);
// No recently freed region has been found, try to provide a hint for placing
// a code region.
if (it == recently_freed_.end() || it->second.empty()) {
if (V8_ENABLE_NEAR_CODE_RANGE_BOOL && !preferred_region.is_empty()) {
auto memory_ranges = base::OS::GetFreeMemoryRangesWithin(
preferred_region.begin(), preferred_region.end(), code_range_size,
alignment);
if (!memory_ranges.empty()) {
result = memory_ranges.front().start;
CHECK(IsAligned(result, alignment));
return result;
}
// The empty memory_ranges means that GetFreeMemoryRangesWithin() API
// is not supported, so use the lowest address from the preferred region
// as a hint because it'll be at least as good as the fallback hint but
// with a higher chances to point to the free address space range.
return RoundUp(preferred_region.begin(), alignment);
}
return RoundUp(FUNCTION_ADDR(&FunctionInStaticBinaryForAddressHint),
alignment);
}
// Try to reuse near code range first.
if (V8_ENABLE_NEAR_CODE_RANGE_BOOL && !preferred_region.is_empty()) {
auto freed_regions_for_size = it->second;
for (auto it_freed = freed_regions_for_size.rbegin();
it_freed != freed_regions_for_size.rend(); ++it_freed) {
Address code_range_start = *it_freed;
if (preferred_region.contains(code_range_start, code_range_size)) {
CHECK(IsAligned(code_range_start, alignment));
freed_regions_for_size.erase((it_freed + 1).base());
return code_range_start;
}
}
}
result = it->second.back();
CHECK(IsAligned(result, alignment));
it->second.pop_back();
return result;
}
void CodeRangeAddressHint::NotifyFreedCodeRange(Address code_range_start,
size_t code_range_size) {
base::MutexGuard guard(&mutex_);
recently_freed_[code_range_size].push_back(code_range_start);
}
CodeRange::~CodeRange() { Free(); }
// static
size_t CodeRange::GetWritableReservedAreaSize() {
return kReservedCodeRangePages * MemoryAllocator::GetCommitPageSize();
}
#define TRACE(...) \
if (v8_flags.trace_code_range_allocation) PrintF(__VA_ARGS__)
bool CodeRange::InitReservation(v8::PageAllocator* page_allocator,
size_t requested) {
DCHECK_NE(requested, 0);
if (V8_EXTERNAL_CODE_SPACE_BOOL) {
page_allocator = GetPlatformPageAllocator();
}
if (requested <= kMinimumCodeRangeSize) {
requested = kMinimumCodeRangeSize;
}
const size_t kPageSize = MemoryChunk::kPageSize;
CHECK(IsAligned(kPageSize, page_allocator->AllocatePageSize()));
// When V8_EXTERNAL_CODE_SPACE_BOOL is enabled the allocatable region must
// not cross the 4Gb boundary and thus the default compression scheme of
// truncating the InstructionStream pointers to 32-bits still works. It's
// achieved by specifying base_alignment parameter.
const size_t base_alignment = V8_EXTERNAL_CODE_SPACE_BOOL
? base::bits::RoundUpToPowerOfTwo(requested)
: kPageSize;
DCHECK_IMPLIES(kPlatformRequiresCodeRange,
requested <= kMaximalCodeRangeSize);
VirtualMemoryCage::ReservationParams params;
params.page_allocator = page_allocator;
params.reservation_size = requested;
params.page_size = kPageSize;
params.jit =
v8_flags.jitless ? JitPermission::kNoJit : JitPermission::kMapAsJittable;
const size_t allocate_page_size = page_allocator->AllocatePageSize();
// TODO(v8:11880): Use base_alignment here once ChromeOS issue is fixed.
Address the_hint =
GetCodeRangeAddressHint()->GetAddressHint(requested, allocate_page_size);
the_hint = RoundDown(the_hint, base_alignment);
constexpr size_t kRadiusInMB =
kMaxPCRelativeCodeRangeInMB > 1024 ? kMaxPCRelativeCodeRangeInMB : 4096;
auto preferred_region = GetPreferredRegion(kRadiusInMB, kPageSize);
TRACE("=== Preferred region: [%p, %p)\n",
reinterpret_cast<void*>(preferred_region.begin()),
reinterpret_cast<void*>(preferred_region.end()));
// For configurations with enabled pointer compression and shared external
// code range we can afford trying harder to allocate code range near .text
// section.
const bool kShouldTryHarder = V8_EXTERNAL_CODE_SPACE_BOOL &&
COMPRESS_POINTERS_IN_SHARED_CAGE_BOOL &&
v8_flags.better_code_range_allocation;
if (kShouldTryHarder) {
// Relax alignment requirement while trying to allocate code range inside
// preferred region.
params.base_alignment = kPageSize;
// TODO(v8:11880): consider using base::OS::GetFreeMemoryRangesWithin()
// to avoid attempts that's going to fail anyway.
VirtualMemoryCage candidate_cage;
// Try to allocate code range at the end of preferred region, by going
// towards the start in steps.
const int kAllocationTries = 16;
params.requested_start_hint =
RoundDown(preferred_region.end() - requested, kPageSize);
Address step =
RoundDown(preferred_region.size() / kAllocationTries, kPageSize);
for (int i = 0; i < kAllocationTries; i++) {
TRACE("=== Attempt #%d, hint=%p\n", i,
reinterpret_cast<void*>(params.requested_start_hint));
if (candidate_cage.InitReservation(params)) {
TRACE("=== Attempt #%d (%p): [%p, %p)\n", i,
reinterpret_cast<void*>(params.requested_start_hint),
reinterpret_cast<void*>(candidate_cage.region().begin()),
reinterpret_cast<void*>(candidate_cage.region().end()));
// Allocation succeeded, check if it's in the preferred range.
if (preferred_region.contains(candidate_cage.region())) break;
// This allocation is not the one we are searhing for.
candidate_cage.Free();
}
if (step == 0) break;
params.requested_start_hint -= step;
}
if (candidate_cage.IsReserved()) {
*static_cast<VirtualMemoryCage*>(this) = std::move(candidate_cage);
}
}
if (!IsReserved()) {
// Last resort, use whatever region we get.
params.base_alignment = base_alignment;
params.requested_start_hint = the_hint;
if (!VirtualMemoryCage::InitReservation(params)) return false;
TRACE("=== Fallback attempt, hint=%p: [%p, %p)\n",
reinterpret_cast<void*>(params.requested_start_hint),
reinterpret_cast<void*>(region().begin()),
reinterpret_cast<void*>(region().end()));
}
if (v8_flags.abort_on_far_code_range &&
!preferred_region.contains(region())) {
// We didn't manage to allocate the code range close enough.
FATAL("Failed to allocate code range close to the .text section");
}
// On some platforms, specifically Win64, we need to reserve some pages at
// the beginning of an executable space. See
// https://cs.chromium.org/chromium/src/components/crash/content/
// app/crashpad_win.cc?rcl=fd680447881449fba2edcf0589320e7253719212&l=204
// for details.
const size_t reserved_area = GetWritableReservedAreaSize();
if (reserved_area > 0) {
CHECK_LE(reserved_area, kPageSize);
// Exclude the reserved area from further allocations.
CHECK(page_allocator_->AllocatePagesAt(base(), kPageSize,
PageAllocator::kNoAccess));
// Commit required amount of writable memory.
if (!reservation()->SetPermissions(base(), reserved_area,
PageAllocator::kReadWrite)) {
return false;
}
#if defined(V8_OS_WIN64)
if (win64_unwindinfo::CanRegisterUnwindInfoForNonABICompliantCodeRange()) {
win64_unwindinfo::RegisterNonABICompliantCodeRange(
reinterpret_cast<void*>(base()), size());
}
#endif // V8_OS_WIN64
}
if (V8_HEAP_USE_PTHREAD_JIT_WRITE_PROTECT &&
params.jit == JitPermission::kMapAsJittable) {
// Should the reserved area ever become non-empty we shouldn't mark it as
// RWX below.
CHECK_EQ(reserved_area, 0);
void* base = reinterpret_cast<void*>(page_allocator_->begin());
size_t size = page_allocator_->size();
if (!params.page_allocator->SetPermissions(
base, size, PageAllocator::kReadWriteExecute)) {
return false;
}
if (!params.page_allocator->DiscardSystemPages(base, size)) return false;
}
return true;
}
// Preferred region for the code range is an intersection of the following
// regions:
// a) [builtins - kMaxPCRelativeDistance, builtins + kMaxPCRelativeDistance)
// b) [RoundDown(builtins, 4GB), RoundUp(builtins, 4GB)) in order to ensure
// Requirement (a) is there to avoid remaping of embedded builtins into
// the code for architectures where PC-relative jump/call distance is big
// enough.
// Requirement (b) is aiming at helping CPU branch predictors in general and
// in case V8_EXTERNAL_CODE_SPACE is enabled it ensures that
// ExternalCodeCompressionScheme works for all pointers in the code range.
// static
base::AddressRegion CodeRange::GetPreferredRegion(size_t radius_in_megabytes,
size_t allocate_page_size) {
#ifdef V8_TARGET_ARCH_64_BIT
// Compute builtins location.
Address embedded_blob_code_start =
reinterpret_cast<Address>(Isolate::CurrentEmbeddedBlobCode());
Address embedded_blob_code_end;
if (embedded_blob_code_start == kNullAddress) {
// When there's no embedded blob use address of a function from the binary
// as an approximation.
embedded_blob_code_start =
FUNCTION_ADDR(&FunctionInStaticBinaryForAddressHint);
embedded_blob_code_end = embedded_blob_code_start + 1;
} else {
embedded_blob_code_end =
embedded_blob_code_start + Isolate::CurrentEmbeddedBlobCodeSize();
}
// Fulfil requirement (a).
constexpr size_t max_size = std::numeric_limits<size_t>::max();
size_t radius = radius_in_megabytes * MB;
Address region_start =
RoundUp(embedded_blob_code_end - radius, allocate_page_size);
if (region_start > embedded_blob_code_end) {
// |region_start| underflowed.
region_start = 0;
}
Address region_end =
RoundDown(embedded_blob_code_start + radius, allocate_page_size);
if (region_end < embedded_blob_code_start) {
// |region_end| overflowed.
region_end = RoundDown(max_size, allocate_page_size);
}
// Fulfil requirement (b).
constexpr size_t k4GB = size_t{4} * GB;
Address four_gb_cage_start = RoundDown(embedded_blob_code_start, k4GB);
Address four_gb_cage_end = four_gb_cage_start + k4GB;
region_start = std::max(region_start, four_gb_cage_start);
region_end = std::min(region_end, four_gb_cage_end);
#ifdef V8_EXTERNAL_CODE_SPACE
// If ExternalCodeCompressionScheme ever changes then the requirements might
// need to be updated.
static_assert(k4GB <= kPtrComprCageReservationSize);
DCHECK_EQ(four_gb_cage_start,
ExternalCodeCompressionScheme::PrepareCageBaseAddress(
embedded_blob_code_start));
#endif // V8_EXTERNAL_CODE_SPACE
return base::AddressRegion(region_start, region_end - region_start);
#else
return {};
#endif // V8_TARGET_ARCH_64_BIT
}
void CodeRange::Free() {
if (IsReserved()) {
#if defined(V8_OS_WIN64)
if (win64_unwindinfo::CanRegisterUnwindInfoForNonABICompliantCodeRange()) {
win64_unwindinfo::UnregisterNonABICompliantCodeRange(
reinterpret_cast<void*>(base()));
}
#endif // V8_OS_WIN64
GetCodeRangeAddressHint()->NotifyFreedCodeRange(
reservation()->region().begin(), reservation()->region().size());
VirtualMemoryCage::Free();
}
}
uint8_t* CodeRange::RemapEmbeddedBuiltins(Isolate* isolate,
const uint8_t* embedded_blob_code,
size_t embedded_blob_code_size) {
base::MutexGuard guard(&remap_embedded_builtins_mutex_);
// Remap embedded builtins into the end of the address range controlled by
// the BoundedPageAllocator.
const base::AddressRegion code_region(page_allocator()->begin(),
page_allocator()->size());
CHECK_NE(code_region.begin(), kNullAddress);
CHECK(!code_region.is_empty());
uint8_t* embedded_blob_code_copy =
embedded_blob_code_copy_.load(std::memory_order_acquire);
if (embedded_blob_code_copy) {
DCHECK(
code_region.contains(reinterpret_cast<Address>(embedded_blob_code_copy),
embedded_blob_code_size));
SLOW_DCHECK(memcmp(embedded_blob_code, embedded_blob_code_copy,
embedded_blob_code_size) == 0);
return embedded_blob_code_copy;
}
const size_t kAllocatePageSize = page_allocator()->AllocatePageSize();
const size_t kCommitPageSize = page_allocator()->CommitPageSize();
size_t allocate_code_size =
RoundUp(embedded_blob_code_size, kAllocatePageSize);
// Allocate the re-embedded code blob in such a way that it will be reachable
// by PC-relative addressing from biggest possible region.
const size_t max_pc_relative_code_range = kMaxPCRelativeCodeRangeInMB * MB;
size_t hint_offset =
std::min(max_pc_relative_code_range, code_region.size()) -
allocate_code_size;
void* hint = reinterpret_cast<void*>(code_region.begin() + hint_offset);
embedded_blob_code_copy =
reinterpret_cast<uint8_t*>(page_allocator()->AllocatePages(
hint, allocate_code_size, kAllocatePageSize,
PageAllocator::kNoAccessWillJitLater));
if (!embedded_blob_code_copy) {
V8::FatalProcessOutOfMemory(
isolate, "Can't allocate space for re-embedded builtins");
}
CHECK_EQ(embedded_blob_code_copy, hint);
if (code_region.size() > max_pc_relative_code_range) {
// The re-embedded code blob might not be reachable from the end part of
// the code range, so ensure that code pages will never be allocated in
// the "unreachable" area.
Address unreachable_start =
reinterpret_cast<Address>(embedded_blob_code_copy) +
max_pc_relative_code_range;
if (code_region.contains(unreachable_start)) {
size_t unreachable_size = code_region.end() - unreachable_start;
void* result = page_allocator()->AllocatePages(
reinterpret_cast<void*>(unreachable_start), unreachable_size,
kAllocatePageSize, PageAllocator::kNoAccess);
CHECK_EQ(reinterpret_cast<Address>(result), unreachable_start);
}
}
size_t code_size = RoundUp(embedded_blob_code_size, kCommitPageSize);
if constexpr (base::OS::IsRemapPageSupported()) {
// By default, the embedded builtins are not remapped, but copied. This
// costs memory, since builtins become private dirty anonymous memory,
// rather than shared, clean, file-backed memory for the embedded version.
// If the OS supports it, we can remap the builtins *on top* of the space
// allocated in the code range, making the "copy" shared, clean, file-backed
// memory, and thus saving sizeof(builtins).
//
// Builtins should start at a page boundary, see
// platform-embedded-file-writer-mac.cc. If it's not the case (e.g. if the
// embedded builtins are not coming from the binary), fall back to copying.
if (IsAligned(reinterpret_cast<uintptr_t>(embedded_blob_code),
kCommitPageSize)) {
bool ok = base::OS::RemapPages(embedded_blob_code, code_size,
embedded_blob_code_copy,
base::OS::MemoryPermission::kReadExecute);
if (ok) {
embedded_blob_code_copy_.store(embedded_blob_code_copy,
std::memory_order_release);
return embedded_blob_code_copy;
}
}
}
if (V8_HEAP_USE_PTHREAD_JIT_WRITE_PROTECT) {
if (!page_allocator()->RecommitPages(embedded_blob_code_copy, code_size,
PageAllocator::kReadWriteExecute)) {
V8::FatalProcessOutOfMemory(isolate,
"Re-embedded builtins: recommit pages");
}
RwxMemoryWriteScope rwx_write_scope(
"Enable write access to copy the blob code into the code range");
memcpy(embedded_blob_code_copy, embedded_blob_code,
embedded_blob_code_size);
} else {
if (!page_allocator()->SetPermissions(embedded_blob_code_copy, code_size,
PageAllocator::kReadWrite)) {
V8::FatalProcessOutOfMemory(isolate,
"Re-embedded builtins: set permissions");
}
memcpy(embedded_blob_code_copy, embedded_blob_code,
embedded_blob_code_size);
if (!page_allocator()->SetPermissions(embedded_blob_code_copy, code_size,
PageAllocator::kReadExecute)) {
V8::FatalProcessOutOfMemory(isolate,
"Re-embedded builtins: set permissions");
}
}
embedded_blob_code_copy_.store(embedded_blob_code_copy,
std::memory_order_release);
return embedded_blob_code_copy;
}
namespace {
CodeRange* process_wide_code_range_ = nullptr;
V8_DECLARE_ONCE(init_code_range_once);
void InitProcessWideCodeRange(v8::PageAllocator* page_allocator,
size_t requested_size) {
CodeRange* code_range = new CodeRange();
if (!code_range->InitReservation(page_allocator, requested_size)) {
V8::FatalProcessOutOfMemory(
nullptr, "Failed to reserve virtual memory for CodeRange");
}
process_wide_code_range_ = code_range;
#ifdef V8_EXTERNAL_CODE_SPACE
#ifdef V8_COMPRESS_POINTERS_IN_SHARED_CAGE
ExternalCodeCompressionScheme::InitBase(
ExternalCodeCompressionScheme::PrepareCageBaseAddress(
code_range->base()));
#endif // V8_COMPRESS_POINTERS_IN_SHARED_CAGE
#endif // V8_EXTERNAL_CODE_SPACE
}
} // namespace
// static
CodeRange* CodeRange::EnsureProcessWideCodeRange(
v8::PageAllocator* page_allocator, size_t requested_size) {
base::CallOnce(&init_code_range_once, InitProcessWideCodeRange,
page_allocator, requested_size);
return process_wide_code_range_;
}
// static
CodeRange* CodeRange::GetProcessWideCodeRange() {
return process_wide_code_range_;
}
} // namespace internal
} // namespace v8
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