Don't crash on invalid checkpoint numbers

Resolves #3764

CMakeLists.txt

@@ -1650,6 +1650,7 @@ set(TESTS_WITHOUT_PROGRAM
   call_exit
   check_patched_pthread
   checkpoint_async_signal_syscalls_1000
+  checkpoint_invalid
   checkpoint_mmap_shared
   checkpoint_prctl_name
   checkpoint_simple

src/DebuggerExtensionCommand.cc

@@ -149,7 +149,11 @@ string invoke_delete_checkpoint(GdbServer& gdb_server, Task*,
   if (!gdb_server.timeline()) {
     return string("Command requires a full debugging session.");
   }
-  int id = stoi(args[0]);
+  char* endptr;
+  long id = strtol(args[0].c_str(), &endptr, 10);
+  if (*endptr) {
+    return string("Invalid checkpoint number ") + args[0] + ".";
+  }
   auto it = gdb_server.checkpoints.find(id);
   if (it != gdb_server.checkpoints.end()) {
     if (it->second.is_explicit == GdbServer::Checkpoint::EXPLICIT) {

src/test/checkpoint_invalid.py

@@ -0,0 +1,21 @@
+from util import *
+
+send_gdb('delete checkpoint')
+expect_gdb('requires an argument')
+
+send_gdb('delete checkpoint x')
+expect_gdb('Invalid checkpoint number')
+
+send_gdb('delete checkpoint 0x1')
+expect_gdb('Invalid checkpoint number')
+
+send_gdb('delete checkpoint -1')
+expect_gdb('No checkpoint number')
+
+send_gdb('delete checkpoint 0')
+expect_gdb('No checkpoint number')
+
+send_gdb('delete checkpoint 99999999999999999999999999999999999999999')
+expect_gdb('No checkpoint number')
+
+ok()

src/test/checkpoint_invalid.run

@@ -0,0 +1,3 @@
+source `dirname $0`/util.sh
+record simple$bitness
+debug_gdb_only checkpoint_invalid