strace: Change implementation to use ptrace()

Author: https://github.com/itamar8910
Commit: https://github.com/SerenityOS/serenity/commit/e5ebdb9bca3
Pull-request: https://github.com/SerenityOS/serenity/pull/1517
Reviewed-by: https://github.com/awesomekling

Libraries/LibC/Makefile

@@ -46,6 +46,7 @@ LIBC_OBJS = \
        sys/socket.o \
        sys/wait.o \
        sys/uio.o \
+       sys/ptrace.o \
        poll.o \
        locale.o \
        arpa/inet.o \

Libraries/LibC/sys/ptrace.cpp

@@ -0,0 +1,44 @@
+/*
+ * 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 <Kernel/Syscall.h>
+#include <errno.h>
+#include <sys/ptrace.h>
+
+extern "C" {
+
+int ptrace(int request, pid_t pid, void* addr, int data)
+{
+    Syscall::SC_ptrace_params params {
+        request,
+        pid,
+        reinterpret_cast<u8*>(addr),
+        data
+    };
+    int rc = syscall(SC_ptrace, &params);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+}

Libraries/LibC/sys/ptrace.h

@@ -0,0 +1,42 @@
+/*
+ * 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 <sys/types.h>
+
+__BEGIN_DECLS
+
+#define PT_TRACE_ME 1
+#define PT_ATTACH 2
+#define PT_CONTINUE 3
+#define PT_SYSCALL 4
+#define PT_GETREGS 5
+#define PT_DETACH 6
+
+int ptrace(int request, pid_t pid, void* addr, int data);
+
+__END_DECLS

Libraries/LibC/unistd.cpp

@@ -45,12 +45,6 @@
 
 extern "C" {
 
-int systrace(pid_t pid)
-{
-    int rc = syscall(SC_systrace, pid);
-    __RETURN_WITH_ERRNO(rc, rc, -1);
-}
-
 int chown(const char* pathname, uid_t uid, gid_t gid)
 {
     if (!pathname) {

Libraries/LibC/unistd.h

@@ -58,7 +58,6 @@ int get_process_name(char* buffer, int buffer_size);
 void dump_backtrace();
 int fsync(int fd);
 void sysbeep();
-int systrace(pid_t);
 int gettid();
 int donate(int tid);
 int set_process_icon(int icon_id);

Userland/strace.cpp

@@ -25,18 +25,34 @@
  */
 
 #include <AK/Assertions.h>
+#include <AK/LogStream.h>
 #include <AK/Types.h>
 #include <Kernel/Syscall.h>
+#include <LibC/sys/arch/i386/regs.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/ptrace.h>
+#include <sys/wait.h>
 #include <unistd.h>
 
 static int usage()
 {
-    printf("usage: strace [-p PID] [command...]\n");
-    return 0;
+    printf("usage: strace [-p pid] [command...]\n");
+    return 1;
+}
+
+static int g_pid = -1;
+
+static void handle_sigint(int)
+{
+    if (g_pid == -1)
+        return;
+
+    if (ptrace(PT_DETACH, g_pid, 0, 0) == -1) {
+        perror("detach");
+    }
 }
 
 int main(int argc, char** argv)
@@ -44,18 +60,17 @@ int main(int argc, char** argv)
     if (argc == 1)
         return usage();
 
-    pid_t pid = -1;
-    bool pid_is_child = false;
-
     if (!strcmp(argv[1], "-p")) {
         if (argc != 3)
             return usage();
-        pid = atoi(argv[2]);
+        g_pid = atoi(argv[2]);
     } else {
-        pid_is_child = true;
-        pid = fork();
+        int pid = fork();
         if (!pid) {
-            kill(getpid(), SIGSTOP);
+            if (ptrace(PT_TRACE_ME, 0, 0, 0) == -1) {
+                perror("traceme");
+                return 1;
+            }
             int rc = execvp(argv[1], &argv[1]);
             if (rc < 0) {
                 perror("execvp");
@@ -63,40 +78,84 @@ int main(int argc, char** argv)
             }
             ASSERT_NOT_REACHED();
         }
+        if (waitpid(pid, nullptr, WSTOPPED) != pid) {
+            perror("waitpid");
+            return 1;
+        }
+        g_pid = pid;
     }
 
-    int fd = systrace(pid);
-    if (fd < 0) {
-        perror("systrace");
+    struct sigaction sa;
+    memset(&sa, 0, sizeof(struct sigaction));
+    sa.sa_handler = handle_sigint;
+    sigaction(SIGINT, &sa, nullptr);
+
+    if (ptrace(PT_ATTACH, g_pid, 0, 0) == -1) {
+        perror("attach");
         return 1;
     }
 
-    if (pid_is_child) {
-        int rc = kill(pid, SIGCONT);
-        if (rc < 0) {
-            perror("kill(pid, SIGCONT)");
-            return 1;
-        }
+    if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
+        perror("waitpid");
+        return 1;
     }
 
     for (;;) {
-        u32 call[5];
-        int nread = read(fd, &call, sizeof(call));
-        if (nread == 0)
-            break;
-        if (nread < 0) {
-            perror("read");
+        if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
+            if (errno == ESRCH)
+                return 0;
+            perror("syscall");
+            return 1;
+        }
+        if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
+            perror("wait_pid");
             return 1;
         }
-        ASSERT(nread == sizeof(call));
-        fprintf(stderr, "%s(%#x, %#x, %#x) = %#x\n", Syscall::to_string((Syscall::Function)call[0]), call[1], call[2], call[3], call[4]);
-    }
 
-    int rc = close(fd);
-    if (rc < 0) {
-        perror("close");
-        return 1;
+        PtraceRegisters regs = {};
+        if (ptrace(PT_GETREGS, g_pid, &regs, 0) == -1) {
+            perror("getregs");
+            return 1;
+        }
+
+        u32 syscall_index = regs.eax;
+        u32 arg1 = regs.edx;
+        u32 arg2 = regs.ecx;
+        u32 arg3 = regs.ebx;
+
+        // skip syscall exit
+        if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
+            if (errno == ESRCH)
+                return 0;
+            perror("syscall");
+            return 1;
+        }
+        if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
+            perror("wait_pid");
+            return 1;
+        }
+
+        if (ptrace(PT_GETREGS, g_pid, &regs, 0) == -1) {
+            if (errno == ESRCH && syscall_index == SC_exit) {
+                regs.eax = 0;
+            } else {
+                perror("getregs");
+                return 1;
+            }
+        }
+
+        u32 res = regs.eax;
+
+        fprintf(stderr, "%s(0x%x, 0x%x, 0x%x)\t=%d\n",
+            Syscall::to_string(
+                (Syscall::Function)syscall_index),
+            arg1,
+            arg2,
+            arg3,
+            res);
     }
 
     return 0;
+
+    return 0;
 }