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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.
#ifndef INCLUDE_V8_UNWINDER_H_
#define INCLUDE_V8_UNWINDER_H_
#include <memory>
#include "v8-embedder-state-scope.h" // NOLINT(build/include_directory)
#include "v8config.h" // NOLINT(build/include_directory)
namespace v8 {
// Holds the callee saved registers needed for the stack unwinder. It is the
// empty struct if no registers are required. Implemented in
// include/v8-unwinder-state.h.
struct CalleeSavedRegisters;
// A RegisterState represents the current state of registers used
// by the sampling profiler API.
struct V8_EXPORT RegisterState {
RegisterState();
~RegisterState();
RegisterState(const RegisterState& other);
RegisterState& operator=(const RegisterState& other);
void* pc; // Instruction pointer.
void* sp; // Stack pointer.
void* fp; // Frame pointer.
void* lr; // Link register (or nullptr on platforms without a link register).
// Callee saved registers (or null if no callee saved registers were stored)
std::unique_ptr<CalleeSavedRegisters> callee_saved;
};
// A StateTag represents a possible state of the VM.
enum StateTag : uint16_t {
JS,
GC,
PARSER,
BYTECODE_COMPILER,
COMPILER,
OTHER,
EXTERNAL,
ATOMICS_WAIT,
IDLE,
LOGGING,
};
// The output structure filled up by GetStackSample API function.
struct SampleInfo {
size_t frames_count; // Number of frames collected.
void* external_callback_entry; // External callback address if VM is
// executing an external callback.
void* context; // Incumbent native context address.
void* embedder_context; // Native context address for embedder state
StateTag vm_state; // Current VM state.
EmbedderStateTag embedder_state; // Current Embedder state
};
struct MemoryRange {
const void* start = nullptr;
size_t length_in_bytes = 0;
};
struct JSEntryStub {
MemoryRange code;
};
struct JSEntryStubs {
JSEntryStub js_entry_stub;
JSEntryStub js_construct_entry_stub;
JSEntryStub js_run_microtasks_entry_stub;
};
/**
* Various helpers for skipping over V8 frames in a given stack.
*
* The unwinder API is only supported on the x64, ARM64 and ARM32 architectures.
*/
class V8_EXPORT Unwinder {
public:
/**
* Attempt to unwind the stack to the most recent C++ frame. This function is
* signal-safe and does not access any V8 state and thus doesn't require an
* Isolate.
*
* The unwinder needs to know the location of the JS Entry Stub (a piece of
* code that is run when C++ code calls into generated JS code). This is used
* for edge cases where the current frame is being constructed or torn down
* when the stack sample occurs.
*
* The unwinder also needs the virtual memory range of all possible V8 code
* objects. There are two ranges required - the heap code range and the range
* for code embedded in the binary.
*
* Available on x64, ARM64 and ARM32.
*
* \param code_pages A list of all of the ranges in which V8 has allocated
* executable code. The caller should obtain this list by calling
* Isolate::CopyCodePages() during the same interrupt/thread suspension that
* captures the stack.
* \param register_state The current registers. This is an in-out param that
* will be overwritten with the register values after unwinding, on success.
* \param stack_base The resulting stack pointer and frame pointer values are
* bounds-checked against the stack_base and the original stack pointer value
* to ensure that they are valid locations in the given stack. If these values
* or any intermediate frame pointer values used during unwinding are ever out
* of these bounds, unwinding will fail.
*
* \return True on success.
*/
static bool TryUnwindV8Frames(const JSEntryStubs& entry_stubs,
size_t code_pages_length,
const MemoryRange* code_pages,
RegisterState* register_state,
const void* stack_base);
/**
* Whether the PC is within the V8 code range represented by code_pages.
*
* If this returns false, then calling UnwindV8Frames() with the same PC
* and unwind_state will always fail. If it returns true, then unwinding may
* (but not necessarily) be successful.
*
* Available on x64, ARM64 and ARM32
*/
static bool PCIsInV8(size_t code_pages_length, const MemoryRange* code_pages,
void* pc);
};
} // namespace v8
#endif // INCLUDE_V8_UNWINDER_H_
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