Better handling of compilation memory limit exceeded errors

Author: prandla

cms/grading/Sandbox.py

@@ -414,11 +414,15 @@ def get_exit_status(self) -> str:
                 return self.EXIT_TIMEOUT_WALL
             else:
                 return self.EXIT_TIMEOUT
+        elif 'cg-oom-killed' in self.log:
+            # OOM killer was activated in the sandbox. It killed either the
+            # main process (in which case the exit status is SG) or a
+            # subprocess (in which case the main process gets to decide how to
+            # handle it, but probably RE). In both cases, we want to
+            # "root-cause" the verdict as "memory limit exceeded".
+            return self.EXIT_MEM_LIMIT
         elif "SG" in status_list:
-            if "cg-oom-killed" in self.meta:
-                return self.EXIT_MEM_LIMIT
-            else:
-                return self.EXIT_SIGNAL
+            return self.EXIT_SIGNAL
         elif "RE" in status_list:
             return self.EXIT_NONZERO_RETURN
         # OK status is not reported in the meta file, it's implicit.

cms/grading/steps/compilation.py

@@ -55,13 +55,16 @@ def N_(message: str):
                  N_("Your submission exceeded the time limit while compiling. "
                     "This might be caused by an excessive use of C++ "
                     "templates, for example.")),
+    HumanMessage("memorylimit",
+                 N_("Compilation memory limit exceeded"),
+                 N_("Your submission exceeded the memory limit while compiling. "
+                    "This might be caused by an excessive use of C++ "
+                    "templates, or too large global variables, for example.")),
     HumanMessage("signal",
-                 N_("Compilation killed with signal %s (could be triggered "
-                    "by violating memory limits)"),
+                 N_("Compilation killed with signal %s"),
                  N_("Your submission was killed with the specified signal. "
-                    "Among other things, this might be caused by exceeding "
-                    "the memory limit for the compilation, and in turn by an "
-                    "excessive use of C++ templates, for example.")),
+                    "This might be caused by a bug in the compiler, "
+                    "for example.")),
 ])
 
 
@@ -136,6 +139,13 @@ def compilation_step(
         text = [COMPILATION_MESSAGES.get("timeout").message]
         return True, False, text, stats
 
+    elif exit_status == Sandbox.EXIT_MEM_LIMIT:
+        # Memory limit: we assume it is the user's fault, and we return the
+        # error to them.
+        logger.debug("Compilation memory limit exceeded.")
+        text = [COMPILATION_MESSAGES.get("memorylimit").message]
+        return True, False, text, stats
+
     elif exit_status == Sandbox.EXIT_SIGNAL:
         # Terminated by signal: we assume again it is the user's fault, and
         # we return the error to them.

cmstestsuite/Tests.py

@@ -196,6 +196,11 @@
          languages=(LANG_CPP,),
          checks=[CheckCompilationFail()]),
 
+    Test('compile-memory-limit',
+         task=batch_fileio, filenames=['compile-memory-limit.%l'],
+         languages=(LANG_CPP,),
+         checks=[CheckCompilationFail()]),
+
     # Various timeout conditions.
 
     Test('timeout-cputime',

cmstestsuite/code/compile-memory-limit.cpp

@@ -0,0 +1,9 @@
+#ifdef EVAL // this file can accidentally OOM editors/language servers...
+#define a "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+#define b a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
+#define c b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b
+#define d c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c
+#define e d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d
+const char* x = e e;
+#endif
+int main() { return 0; }