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// Copyright 2019 The Chromium 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 "base/profiler/stack_copier.h"
#include "base/compiler_specific.h"
namespace base {
StackCopier::~StackCopier() = default;
// static
uintptr_t StackCopier::RewritePointerIfInOriginalStack(
const uint8_t* original_stack_bottom,
const uintptr_t* original_stack_top,
const uint8_t* stack_copy_bottom,
uintptr_t pointer) {
auto original_stack_bottom_uint =
auto original_stack_top_uint =
auto stack_copy_bottom_uint = reinterpret_cast<uintptr_t>(stack_copy_bottom);
if (pointer < original_stack_bottom_uint ||
pointer >= original_stack_top_uint)
return pointer;
return stack_copy_bottom_uint + (pointer - original_stack_bottom_uint);
// static
const uint8_t* StackCopier::CopyStackContentsAndRewritePointers(
const uint8_t* original_stack_bottom,
const uintptr_t* original_stack_top,
int platform_stack_alignment,
uintptr_t* stack_buffer_bottom) {
const uint8_t* byte_src = original_stack_bottom;
// The first address in the stack with pointer alignment. Pointer-aligned
// values from this point to the end of the stack are possibly rewritten using
// RewritePointerIfInOriginalStack(). Bytes before this cannot be a pointer
// because they occupy less space than a pointer would.
const uint8_t* first_aligned_address = reinterpret_cast<uint8_t*>(
(reinterpret_cast<uintptr_t>(byte_src) + sizeof(uintptr_t) - 1) &
~(sizeof(uintptr_t) - 1));
// The stack copy bottom, which is offset from |stack_buffer_bottom| by the
// same alignment as in the original stack. This guarantees identical
// alignment between values in the original stack and the copy. This uses the
// platform stack alignment rather than pointer alignment so that the stack
// copy is aligned to platform expectations.
uint8_t* stack_copy_bottom =
reinterpret_cast<uint8_t*>(stack_buffer_bottom) +
(reinterpret_cast<uintptr_t>(byte_src) & (platform_stack_alignment - 1));
uint8_t* byte_dst = stack_copy_bottom;
// Copy bytes verbatim up to the first aligned address.
for (; byte_src < first_aligned_address; ++byte_src, ++byte_dst)
*byte_dst = *byte_src;
// Copy the remaining stack by pointer-sized values, rewriting anything that
// looks like a pointer into the stack.
const uintptr_t* src = reinterpret_cast<const uintptr_t*>(byte_src);
uintptr_t* dst = reinterpret_cast<uintptr_t*>(byte_dst);
for (; src < original_stack_top; ++src, ++dst) {
*dst = RewritePointerIfInOriginalStack(
original_stack_bottom, original_stack_top, stack_copy_bottom, *src);
return stack_copy_bottom;
} // namespace base