Add 'press D to attach debugger' feature

Action.c

@@ -25,10 +25,15 @@ in the source distribution for its full text.
 #include <ctype.h>
 #include <math.h>
 #include <pwd.h>
+#include <signal.h>
 #include <stdlib.h>
 #include <stdbool.h>
 #include <sys/param.h>
 #include <sys/time.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <termios.h>
+#include <unistd.h>
 
 Object* Action_pickFromVector(State* st, Panel* list, int x, bool followProcess) {
    Panel* panel = st->panel;
@@ -378,6 +383,123 @@ static Htop_Reaction actionStrace(State* st) {
    return HTOP_REFRESH | HTOP_REDRAW_BAR;
 }
 
+/**
+ * Creates a subprocess with the given argv.
+ *
+ * argv must be a null-terminated array of strings,
+ * and will be passed to execvp.
+ *
+ * The subprocess is launched as a child process,
+ * in its own foreground process group;
+ * this decouples signals like SIGINT from htop.
+ */
+bool launchSubProcess(char *const argv[]) {
+   endwin();
+
+   // backup the current terminal settings
+   struct termios old_attrs;
+   if (tcgetattr(STDIN_FILENO, &old_attrs) < 0)
+   {
+      perror("tcgetattr()");
+      return false;
+   }
+
+   // backup the current foreground process group
+   pid_t old_pgrp = tcgetpgrp(STDIN_FILENO);
+   if (old_pgrp < 0) {
+      perror("tcgetpgrp()");
+      return false;
+   }
+
+   pid_t child_pid = fork();
+   if (child_pid == -1) {
+      perror("fork()");
+      return false;
+   }
+
+   if (child_pid == 0) {
+      // this is the child process. launch the subprocess
+      printf("htop: launching");
+      for (size_t i = 0; argv[i] != NULL; i++) {
+         printf(" %s", argv[i]);
+      }
+      putchar('\n');
+      execvp(argv[0], argv);
+      // we should never reach this line.
+      // most likely cause of error: argv[0] doesn't exist
+      perror("excecvp()");
+      exit(1);
+   }
+
+   // setup a process group for the child
+   setpgid(child_pid, child_pid);
+   tcsetpgrp(STDIN_FILENO, child_pid);
+   // if the child prints to stdout between setpgid and tcsetpgrp,
+   // it is stopped; we need to send SIGCONT to prevent this.
+   kill(child_pid, SIGCONT);
+
+   // wait for the child to terminate.
+   int child_status;
+   while (waitpid(child_pid, &child_status, 0) == child_pid) {}
+
+   // restore the foreground process group
+   // we must ignore SIGTTOU while we do this
+   void (*old_handler)(int) = signal(SIGTTOU, SIG_IGN);
+   tcsetpgrp(STDIN_FILENO, old_pgrp);
+   if (old_handler != SIG_ERR) {
+      signal(SIGTTOU, old_handler);
+   }
+
+   // restore the terminal settings
+   if (tcsetattr(STDIN_FILENO, TCSADRAIN, &old_attrs) < 0) {
+      perror("tcsetattr()");
+      return false;
+   }
+
+   // check the child exit status
+   if (WIFEXITED(child_status)) {
+      if (WEXITSTATUS(child_status) == 0) {
+         // all good!
+         return true;
+      }
+      printf("child exited with %d\n", WEXITSTATUS(child_status));
+      return false;
+   } else if (WIFSIGNALED(child_status)) {
+      printf("child killed (signal %d)\n", WTERMSIG(child_status));
+      return false;
+   } else {
+      printf("unexpected wait() status: 0x%x\n", child_status);
+      return false;
+   }
+}
+
+static Htop_Reaction actionDebugger(State* st) {
+   Settings* settings = st->settings;
+   Process* p = (Process*) Panel_getSelected(st->panel);
+   if (!p) return HTOP_OK;
+
+   // prepare the argv for the debugger subprocess
+   char *arg0 = settings->debuggerTool;
+   char arg1[] = "-p";
+   char arg2[64];
+   xSnprintf(arg2, sizeof(arg2), "%d", (int) p->pid);
+   char *const argv[] = { arg0, arg1, arg2, NULL };
+
+   if (!launchSubProcess(argv)) {
+      // something went wrong
+      // pause to allow the user to read the error message(s)
+      printf("press ENTER to continue");
+      int c = 0;
+      while (c != EOF && c != '\n') {
+         c = getchar();
+      }
+   }
+
+   refresh();
+   CRT_enableDelay();
+   return HTOP_REFRESH | HTOP_REDRAW_BAR | HTOP_UPDATE_PANELHDR;
+}
+
 static Htop_Reaction actionTag(State* st) {
    Process* p = (Process*) Panel_getSelected(st->panel);
    if (!p) return HTOP_OK;
@@ -423,6 +545,7 @@ static const struct { const char* key; const char* info; } helpRight[] = {
    { .key = "      i: ", .info = "set IO priority" },
    { .key = "      l: ", .info = "list open files with lsof" },
    { .key = "      s: ", .info = "trace syscalls with strace" },
+   { .key = "      D: ", .info = "attach debugger" },
    { .key = "         ", .info = "" },
    { .key = " F2 C S: ", .info = "setup" },
    { .key = "   F1 h: ", .info = "show this help screen" },
@@ -576,6 +699,7 @@ void Action_setBindings(Htop_Action* keys) {
    keys[KEY_F(2)] = actionSetup;
    keys['l'] = actionLsof;
    keys['s'] = actionStrace;
+   keys['D'] = actionDebugger;
    keys[' '] = actionTag;
    keys['\014'] = actionRedraw; // Ctrl+L
    keys[KEY_F(1)] = actionHelp;

Settings.c

@@ -24,6 +24,7 @@ void Settings_delete(Settings* this) {
       String_freeArray(this->columns[i].names);
       free(this->columns[i].modes);
    }
+   free(this->debuggerTool);
    free(this);
 }
 
@@ -181,7 +182,10 @@ static bool Settings_read(Settings* this, const char* fileName) {
       } else if (String_eq(option[0], "color_scheme")) {
          this->colorScheme = atoi(option[1]);
          if (this->colorScheme < 0 || this->colorScheme >= LAST_COLORSCHEME) this->colorScheme = 0;
-     } else if (String_eq(option[0], "enable_mouse")) {
+      } else if (String_eq(option[0], "debugger_tool")) {
+         this->debuggerTool = String_trim(option[1]);
+         if (strlen(this->debuggerTool) == 0) this->debuggerTool = xStrdup("gdb");
+      } else if (String_eq(option[0], "enable_mouse")) {
          this->enableMouse = atoi(option[1]);
       } else if (String_eq(option[0], "left_meters")) {
          Settings_readMeters(this, option[1], 0);
@@ -272,6 +276,7 @@ bool Settings_write(Settings* this) {
    fprintf(fd, "update_process_names=%d\n", (int) this->updateProcessNames);
    fprintf(fd, "account_guest_in_cpu_meter=%d\n", (int) this->accountGuestInCPUMeter);
    fprintf(fd, "color_scheme=%d\n", (int) this->colorScheme);
+   fprintf(fd, "debugger_tool=%s\n", this->debuggerTool);
    fprintf(fd, "enable_mouse=%d\n", (int) this->enableMouse);
    fprintf(fd, "delay=%d\n", (int) this->delay);
    fprintf(fd, "left_meters="); writeMeters(this, fd, 0);
@@ -353,6 +358,7 @@ Settings* Settings_new(int cpuCount) {
       CRT_restorePrivileges();
    }
    this->colorScheme = 0;
+   this->debuggerTool = xStrdup("gdb");
    this->enableMouse = true;
    this->changed = false;
    this->delay = DEFAULT_DELAY;

Settings.h

@@ -25,6 +25,7 @@ typedef struct Settings_ {
    ProcessField* fields;
    int flags;
    int colorScheme;
+   char *debuggerTool;
    int delay;
 
    int cpuCount;

TESTPLAN

@@ -73,7 +73,9 @@ Main screen:
 
       <F2>, <C>, <S> - enter Setup screen.
 
-      <D>, <E> - do nothing.
+      <D> - attach debugger (must be allowed by ptrace_scope)
+
+      <E> - do nothing.
 
       <F> - follow process.
 

htop.1.in

@@ -115,6 +115,10 @@ update of system calls issued by the process.
 .B l
 Display open files for a process: if lsof(1) is installed, pressing this key
 will display the list of file descriptors opened by the process.
+.B D
+Attach debugger to process: if the configured debugger tool (default: gdb(1))
+is installed, pressing this key will launch and attach it to the currently
+selected process.
 .TP
 .B F1, h, ?
 Go to the help screen