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.

Libraries/LibDebug/DebugSession.cpp

@@ -0,0 +1,213 @@
+/*
+ * 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;
+}