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Userland: Add "functrace" utility

functrace traces the function calls a program makes.
It's like strace, but for userspace.

It works by using Debugging functionality to insert breakpoints
at call&ret instructions.
This commit is contained in:
Itamar 2020-04-12 21:45:04 +03:00 committed by Andreas Kling
parent 13865c7c3d
commit f4418361c4
8 changed files with 175 additions and 4 deletions

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/*
* Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "DebugSession.h"
#include <AK/Optional.h>
#include <stdlib.h>
DebugSession::DebugSession(int pid)
: m_debugee_pid(pid)
, m_executable(String::format("/proc/%d/exe", pid))
, m_elf(reinterpret_cast<u8*>(m_executable.data()), m_executable.size())
{
}
DebugSession::~DebugSession()
{
if (!m_is_debugee_dead) {
if (ptrace(PT_DETACH, m_debugee_pid, 0, 0) < 0) {
perror("PT_DETACH");
}
}
}
OwnPtr<DebugSession> DebugSession::exec_and_attach(const String& command)
{
int pid = fork();
if (!pid) {
if (ptrace(PT_TRACE_ME, 0, 0, 0) < 0) {
perror("PT_TRACE_ME");
exit(1);
}
auto parts = command.split(' ');
ASSERT(!parts.is_empty());
const char** args = (const char**)calloc(parts.size() + 1, sizeof(const char*));
for (size_t i = 0; i < parts.size(); i++) {
args[i] = parts[i].characters();
}
int rc = execvp(args[0], const_cast<char**>(args));
if (rc < 0) {
perror("execvp");
}
ASSERT_NOT_REACHED();
}
if (waitpid(pid, nullptr, WSTOPPED) != pid) {
perror("waitpid");
return nullptr;
}
if (ptrace(PT_ATTACH, pid, 0, 0) < 0) {
perror("PT_ATTACH");
return nullptr;
}
if (waitpid(pid, nullptr, WSTOPPED) != pid) {
perror("waitpid");
return nullptr;
}
if (ptrace(PT_CONTINUE, pid, 0, 0) < 0) {
perror("continue");
return nullptr;
}
// We want to continue until the exit from the 'execve' sycsall.
// This ensures that when we start debugging the process
// it executes the target image, and not the forked image of the tracing process.
// NOTE: we only need to do this when we are debugging a new process (i.e not attaching to a process that's already running!)
if (waitpid(pid, nullptr, WSTOPPED) != pid) {
perror("wait_pid");
return nullptr;
}
return make<DebugSession>(pid);
}
bool DebugSession::poke(u32* address, u32 data)
{
if (ptrace(PT_POKE, m_debugee_pid, (void*)address, data) < 0) {
perror("PT_POKE");
return false;
}
return true;
}
Optional<u32> DebugSession::peek(u32* address) const
{
Optional<u32> result;
int rc = ptrace(PT_PEEK, m_debugee_pid, (void*)address, 0);
if (errno == 0)
result = static_cast<u32>(rc);
return result;
}
bool DebugSession::insert_breakpoint(void* address)
{
// We insert a software breakpoint by
// patching the first byte of the instruction at 'address'
// with the breakpoint instruction (int3)
if (m_breakpoints.contains(address))
return false;
auto original_bytes = peek(reinterpret_cast<u32*>(address));
if (!original_bytes.has_value())
return false;
BreakPoint breakpoint { address, original_bytes.value(), BreakPointState::Disabled };
m_breakpoints.set(address, breakpoint);
enable_breakpoint(breakpoint);
return true;
}
bool DebugSession::disable_breakpoint(const BreakPoint& breakpoint)
{
ASSERT(m_breakpoints.contains(breakpoint.address));
if (!poke(reinterpret_cast<u32*>(reinterpret_cast<char*>(breakpoint.address)), breakpoint.original_first_word))
return false;
auto bp = m_breakpoints.get(breakpoint.address).value();
bp.state = BreakPointState::Disabled;
m_breakpoints.set(bp.address, bp);
return true;
}
bool DebugSession::enable_breakpoint(const BreakPoint& breakpoint)
{
ASSERT(m_breakpoints.contains(breakpoint.address));
if (!poke(reinterpret_cast<u32*>(breakpoint.address), (breakpoint.original_first_word & ~(uint32_t)0xff) | BREAKPOINT_INSTRUCTION))
return false;
auto bp = m_breakpoints.get(breakpoint.address).value();
bp.state = BreakPointState::Enabled;
m_breakpoints.set(bp.address, bp);
return true;
}
PtraceRegisters DebugSession::get_registers() const
{
PtraceRegisters regs;
if (ptrace(PT_GETREGS, m_debugee_pid, &regs, 0) < 0) {
perror("PT_GETREGS");
ASSERT_NOT_REACHED();
}
return regs;
}
void DebugSession::set_registers(const PtraceRegisters& regs)
{
if (ptrace(PT_SETREGS, m_debugee_pid, reinterpret_cast<void*>(&const_cast<PtraceRegisters&>(regs)), 0) < 0) {
perror("PT_SETREGS");
ASSERT_NOT_REACHED();
}
}
void DebugSession::continue_debugee()
{
if (ptrace(PT_CONTINUE, m_debugee_pid, 0, 0) < 0) {
perror("continue");
ASSERT_NOT_REACHED();
}
}
void* DebugSession::single_step()
{
auto regs = get_registers();
constexpr u32 TRAP_FLAG = 0x100;
regs.eflags |= TRAP_FLAG;
set_registers(regs);
continue_debugee();
if (waitpid(m_debugee_pid, 0, WSTOPPED) != m_debugee_pid) {
perror("waitpid");
ASSERT_NOT_REACHED();
}
regs = get_registers();
regs.eflags &= ~(TRAP_FLAG);
set_registers(regs);
return (void*)regs.eip;
}

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/*
* Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <AK/Demangle.h>
#include <AK/HashMap.h>
#include <AK/MappedFile.h>
#include <AK/Optional.h>
#include <AK/OwnPtr.h>
#include <AK/String.h>
#include <LibC/sys/arch/i386/regs.h>
#include <LibELF/Loader.h>
#include <signal.h>
#include <stdio.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <unistd.h>
class DebugSession {
public:
static OwnPtr<DebugSession> exec_and_attach(const String& command);
// Has to be public for OwnPtr::make
DebugSession(int pid);
~DebugSession();
int pid() const { return m_debugee_pid; }
bool poke(u32* address, u32 data);
Optional<u32> peek(u32* address) const;
enum class BreakPointState {
Enabled,
Disabled,
};
struct BreakPoint {
void* address;
u32 original_first_word;
BreakPointState state;
};
bool insert_breakpoint(void* address);
bool disable_breakpoint(const BreakPoint&);
bool enable_breakpoint(const BreakPoint&);
PtraceRegisters get_registers() const;
void set_registers(const PtraceRegisters&);
void continue_debugee();
void* single_step();
template<typename Callback>
void run(Callback callback);
const ELF::Loader& elf() const { return m_elf; }
const MappedFile& executable() const { return m_executable; }
enum DebugDecision {
Continue,
SingleStep,
Detach,
Kill,
};
enum DebugBreakReason {
Breakpoint,
Exited,
};
private:
// x86 breakpoint instruction "int3"
static constexpr u8 BREAKPOINT_INSTRUCTION
= 0xcc;
int m_debugee_pid { -1 };
bool m_is_debugee_dead { false };
MappedFile m_executable;
ELF::Loader m_elf;
HashMap<void*, BreakPoint> m_breakpoints;
};
template<typename Callback>
void DebugSession::run(Callback callback)
{
enum class State {
FreeRun,
ConsecutiveBreakpoint,
SingleStep,
};
State state { State::FreeRun };
for (;;) {
if (state == State::FreeRun) {
continue_debugee();
int wstatus = 0;
if (waitpid(m_debugee_pid, &wstatus, WSTOPPED | WEXITED) != m_debugee_pid) {
perror("waitpid");
ASSERT_NOT_REACHED();
}
// FIXME: This check actually only checks whether the debugee
// stopped because it hit a breakpoint/is in single stepping mode or not
if (WSTOPSIG(wstatus) != SIGTRAP) {
callback(DebugBreakReason::Exited, Optional<PtraceRegisters>());
m_is_debugee_dead = true;
break;
}
}
auto regs = get_registers();
Optional<BreakPoint> current_breakpoint;
if (state == State::FreeRun) {
current_breakpoint = m_breakpoints.get((void*)((u32)regs.eip - 1));
} else {
current_breakpoint = m_breakpoints.get((void*)regs.eip);
}
if (current_breakpoint.has_value()) {
// We want to make the breakpoint transparrent to the user of the debugger
regs.eip = reinterpret_cast<u32>(current_breakpoint.value().address);
set_registers(regs);
disable_breakpoint(current_breakpoint.value());
}
DebugDecision decision = callback(DebugBreakReason::Breakpoint, regs);
if (decision == DebugDecision::Continue) {
state = State::FreeRun;
}
if (current_breakpoint.has_value()) {
// Re-enable the breakpoint
auto stopped_address = single_step();
enable_breakpoint(current_breakpoint.value());
// If there is another breakpoint after the current one,
// Then we are already on it (because of single_step)
auto breakpoint_at_next_instruction = m_breakpoints.get(stopped_address);
if (breakpoint_at_next_instruction.has_value()
&& breakpoint_at_next_instruction.value().state == BreakPointState::Enabled) {
state = State::ConsecutiveBreakpoint;
}
}
if (decision == DebugDecision::SingleStep) {
state = State::SingleStep;
} else {
// TODO: implement DebugDecision:: Kill, Detach
ASSERT(decision == DebugDecision::Continue);
}
if (state == State::SingleStep) {
single_step();
}
}
}

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OBJS = \
DebugSession.o
LIBRARY = libdebug.a
install:
mkdir -p $(SERENITY_BASE_DIR)/Root/usr/include/LibDebug/
cp *.h $(SERENITY_BASE_DIR)/Root/usr/include/LibDebug/
cp $(LIBRARY) $(SERENITY_BASE_DIR)/Root/usr/lib/
include ../../Makefile.common