github.com/tompreston/snapd@v0.0.0-20210817193607-954edfcb9611/cmd/snap-gdb-shim/snap-gdbserver-shim.c (about)

     1  /*
     2   * Copyright (C) 2020 Canonical Ltd
     3   *
     4   * This program is free software: you can redistribute it and/or modify
     5   * it under the terms of the GNU General Public License version 3 as
     6   * published by the Free Software Foundation.
     7   *
     8   * This program is distributed in the hope that it will be useful,
     9   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    10   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    11   * GNU General Public License for more details.
    12   *
    13   * You should have received a copy of the GNU General Public License
    14   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    15   *
    16   */
    17  
    18  #include <signal.h>
    19  #include <stdio.h>
    20  #include <stdlib.h>
    21  #include <unistd.h>
    22  
    23  #include "../libsnap-confine-private/utils.h"
    24  
    25  int main(int argc, char **argv) {
    26      if (sc_is_debug_enabled()) {
    27          for (int i = 0; i < argc; i++) {
    28              fprintf(stderr, "-%s-\n", argv[i]);
    29          }
    30      }
    31      if (argc < 2) {
    32          fprintf(stderr, "missing a command to execute");
    33          abort();
    34      }
    35      // Signal to "snap run" that we are ready to get a debugger attached. When a
    36      // debugger gets attached it will stop the binary at whatever point the
    37      // binary is executing. So we cannot have clever code here that e.g. waits
    38      // for a debugger to get attached because that code would also get
    39      // stoppped/debugged by that debugger and that would be confusing for the
    40      // user.
    41      //
    42      // once a debugger is attached we expect it to send:
    43      //  "continue; signal SIGCONT"
    44      raise(SIGSTOP);
    45  
    46      // signal gdb to stop here
    47      printf("\n\n");
    48      printf("Welcome to `snap run --gdbserver`.\n");
    49      printf("You are right before your application is execed():\n");
    50      printf("- set any options you may need\n");
    51      printf("- (optionally) set a breakpoint in 'main'\n");
    52      printf("- use 'cont' to start\n");
    53      printf("\n\n");
    54      raise(SIGTRAP);
    55  
    56      const char *executable = argv[1];
    57      execv(executable, (char *const *)&argv[1]);
    58      perror("execv failed");
    59      // very different exit code to make an execve failure easy to distinguish
    60      return 101;
    61  }