gdbstub, postmortem: clean up

- Move GDB stub hooks into a separate file, provide header for it
- Use syscall instruction raise user mode exception
- Remove unused code in postmortem.c

fixup

fixup

cores/esp8266/gdb_hooks.h

@@ -0,0 +1,57 @@
+/*
+ gdb_hooks.h - Hooks for GDB Stub library
+ Copyright (c) 2018 Ivan Grokhotkov.  All right reserved.
+
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Initialize GDB stub, if present
+ * 
+ * By default, this function is a no-op. When GDBStub library is linked,
+ * this function is overriden and does necessary initialization of that library.
+ * Called early at startup.
+ */
+void gdb_init(void);
+
+/**
+ * @brief Break into GDB, if present
+ * 
+ * By default, this function is a no-op. When GDBStub library is linked,
+ * this function is overriden and triggers entry into the debugger, which
+ * looks like a breakpoint hit.
+ */
+void gdb_do_break(void);
+
+/**
+ * @brief Check if GDB stub is present.
+ * 
+ * By default, this function returns false. When GDBStub library is linked,
+ * this function is overriden and returns true. Can be used to check whether
+ * GDB is used.
+ * 
+ * @return true if GDB stub is present
+ */
+bool gdb_present(void);
+
+#ifdef __cplusplus
+}
+#endif