gdb: patch sigaltstack

Avoid double allocation of alternative stack. Genode's sigaltstack variant
allocates the stack with alloc_secondary_stack. Disable the warning of
sigaltstack by using explicitly the nullptr in ss_sp.

Issue #5305

repos/ports/ports/gdb.hash

@@ -1 +1 @@
-cb221184908b1a309ae71498720d3c8f1322d87c
+0c95cb9312f8d0d7ad7f996c5df482d993dacf77

repos/ports/src/noux-pkg/gdb/patches/series

@@ -8,3 +8,4 @@ non_stop.patch
 memory_map.patch
 first_inferior.patch
 symlinks.patch
+sigaltstack.patch

repos/ports/src/noux-pkg/gdb/patches/sigaltstack.patch

@@ -0,0 +1,30 @@
+sigaltstack.patch
+
+diff --git a/gdbsupport/alt-stack.h b/gdbsupport/alt-stack.h
+index 1424793..49332a6 100644
+--- a/gdbsupport/alt-stack.h
++++ b/gdbsupport/alt-stack.h
+@@ -37,7 +37,23 @@ class alternate_signal_stack
+   alternate_signal_stack ()
+   {
+ #ifdef HAVE_SIGALTSTACK
++
++#ifdef __GENODE__
++    /*
++     * Stack is allocated within sigaltstack invocation on Genode's Libc,
++     * see issue #5305
++     *
++     * The actual stack pointer is stored in m_stack, which is private,
++     * and thus seems not to be used directly by gdb code in any form.
++     *
++     * The m_stack is a smart pointer, which on destruction frees up the
++     * stored pointer (nullptr). xfree explicitly checks for nullptr and
++     * ignore the attempt, so it should be fine here to use nullptr.
++     */
++    m_stack.reset (nullptr);
++#else
+     m_stack.reset ((char *) xmalloc (SIGSTKSZ));
++#endif
+ 
+     stack_t stack;
+     stack.ss_sp = m_stack.get ();

repos/ports/src/noux-pkg/gdb/target.inc

@@ -8,6 +8,8 @@ CONFIGURE_ARGS += --program-prefix=$(PROGRAM_PREFIX) \
 CONFIGURE_ARGS += --without-expat
 CPPFLAGS += -DHAVE_LIBEXPAT=1
 
+CPPFLAGS += -D__GENODE__
+
 # prevent use of host libgmp in configure test
 CONFIGURE_ARGS += --without-libgmp-prefix