From 0c5df0036c5d8975d4c986f624a4de5d3042c79f Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Thu, 18 Jul 2024 17:11:41 +0200
Subject: [PATCH] libc: support to execute signal on separate stack

With the commit LibC signals will be executed on a separate stack and
not anymore on the kernel or user stack.

Fixes #5305
---
 repos/libports/src/lib/libc/internal/signal.h | 50 ++++++++++++++++++-
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/repos/libports/src/lib/libc/internal/signal.h b/repos/libports/src/lib/libc/internal/signal.h
index 691e86b18e..d3cd395f65 100644
--- a/repos/libports/src/lib/libc/internal/signal.h
+++ b/repos/libports/src/lib/libc/internal/signal.h
@@ -22,6 +22,7 @@
 #include <signal.h>
 
 /* libc-internal includes */
+#include <internal/call_func.h>
 #include <internal/types.h>
 
 namespace Libc { struct Signal; }
@@ -60,6 +61,52 @@ struct Libc::Signal : Noncopyable
 
 		pid_t const _local_pid;
 
+		void  * _signal_stack   { };
+		jmp_buf _signal_context { };
+
+		struct Signal_arguments
+		{
+			Signal  & signal;
+			Pending & pending;
+
+			Signal_arguments(Signal &signal, Pending &pending)
+			: signal(signal), pending(pending) { }
+		};
+
+		static void _signal_entry(Signal_arguments &arg)
+		{
+			arg.signal._execute_signal_handler(arg.pending.n);
+			arg.signal._charged_signals[arg.pending.n].destruct();
+
+			_longjmp(arg.signal._signal_context, 1);
+		}
+
+		void _execute_on_signal_stack(Pending &pending)
+		{
+			if (!_signal_stack) {
+				auto myself = Thread::myself();
+				if (myself)
+					_signal_stack = { myself->alloc_secondary_stack("signal", 16 * 1024) };
+			}
+
+			if (!_signal_stack) {
+				error("signal stack allocation failed");
+				return;
+			}
+
+			/* save continuation of current stack */
+			if (!_setjmp(_signal_context)) {
+
+				Signal_arguments arg(*this, pending);
+
+				/* _setjmp() returned directly -> switch to signal stack */
+				call_func(_signal_stack, (void *)_signal_entry, (void *)&arg);
+
+				/* never reached */
+			}
+			/* _setjmp() returned after _longjmp() */
+		}
+
 	public:
 
 		Signal(pid_t local_pid) : _local_pid(local_pid) { }
@@ -87,8 +134,7 @@ struct Libc::Signal : Noncopyable
 			_nesting_level++;
 
 			_pending_signals.for_each([&] (Pending &pending) {
-				_execute_signal_handler(pending.n);
-				_charged_signals[pending.n].destruct();
+				_execute_on_signal_stack(pending);
 			});
 
 			_nesting_level--;