libmain: Add extraStackOverflowHandler

src/libmain/shared.hh

@@ -113,5 +113,24 @@ struct PrintFreed
 /* Install a SIGSEGV handler to detect stack overflows. */
 void detectStackOverflow();
 
+/* Pluggable behavior to run before _exit(1) in case of a stack overflow.
+
+   Default value: do nothing, return immediately.
+
+   This is called by the handler installed by detectStackOverflow().
+
+   This gives Nix library consumers a limit opportunity to report the error
+   condition.
+
+   NOTE: Use with diligence, because this runs in the signal handler, with very
+   limited stack space and a potentially a corrupted heap, all while the failed
+   thread is blocked indefinitely. All functions called must be reentrant. */
+extern std::function<void(siginfo_t * info, void * ctx)> stackOverflowHandler;
+
+/* The default, robust implementation of stackOverflowHandler.
+
+   Prints an error message directly to stderr using a syscall instead of the
+   logger. Exits the process immediately after. */
+void defaultStackOverflowHandler(siginfo_t * info, void * ctx);
 
 }