ircd::ctx: Split exception_handler w/ cxxabi header requirement.

include/ircd/ctx/exception_handler.h

@@ -11,11 +11,10 @@
 #pragma once
 #define HAVE_IRCD_CTX_EXCEPTION_HANDLER_H
 
-namespace ircd::ctx {
-inline namespace this_ctx
+namespace ircd::ctx
 {
 	struct exception_handler;
-}}
+}
 
 /// An instance of exception_handler must be present to allow a context
 /// switch inside a catch block. This is due to ABI limitations that stack
@@ -28,9 +27,14 @@ inline namespace this_ctx
 ///
 /// The exception cannot then be rethrown. DO NOT RETHROW THE EXCEPTION.
 ///
-struct ircd::ctx::this_ctx::exception_handler
+struct ircd::ctx::exception_handler
 :std::exception_ptr
 {
+	static uint uncaught_exceptions(const uint &) noexcept;
+	static uint uncaught_exceptions() noexcept;
+	static void end_catch() noexcept;
+
+  public:
 	exception_handler() noexcept;
 	exception_handler(exception_handler &&) = delete;
 	exception_handler(const exception_handler &) = delete;

ircd/Makefile.am

@@ -149,6 +149,7 @@ libircd_la_SOURCES += prof.cc
 libircd_la_SOURCES += fs.cc
 libircd_la_SOURCES += ios.cc
 libircd_la_SOURCES += ctx.cc
+libircd_la_SOURCES += ctx_eh.cc
 libircd_la_SOURCES += ctx_ole.cc
 if AIO
 libircd_la_SOURCES += fs_aio.cc

ircd/ctx.cc

@@ -8,7 +8,6 @@
 // copyright notice and this permission notice is present in all copies. The
 // full license for this software is available in the LICENSE file.
 
-#include <cxxabi.h>
 #include <ircd/asio.h>
 #include "ctx.h"
 
@@ -756,30 +755,6 @@ noexcept
 	interruptible(theirs, std::nothrow);
 }
 
-//
-// exception_handler
-//
-
-ircd::ctx::this_ctx::exception_handler::exception_handler()
-noexcept
-:std::exception_ptr
-{
-	std::current_exception()
-}
-{
-	assert(bool(*this));
-
-	#ifdef HAVE_CXXABI_H
-	if(current)
-		__cxxabiv1::__cxa_end_catch();
-	#endif
-
-	// We don't yet support more levels of exceptions; after ending this
-	// catch we can't still be in another one. This doesn't apply if we're
-	// not on any ctx currently.
-	assert(!current || !std::uncaught_exceptions());
-}
-
 //
 // critical_assertion
 //
@@ -996,14 +971,6 @@ ircd::ctx::continuation::noop_interruptor{[]
 	return;
 }};
 
-#ifdef HAVE_CXXABI_H
-struct __cxxabiv1::__cxa_eh_globals
-{
-	__cxa_exception *caughtExceptions;
-	unsigned int uncaughtExceptions;
-};
-#endif
-
 //
 // continuation
 //
@@ -1025,7 +992,7 @@ ircd::ctx::continuation::continuation(const predicate &pred,
 }
 ,uncaught_exceptions
 {
-	uint(std::uncaught_exceptions())
+	exception_handler::uncaught_exceptions(0)
 }
 {
 	assert(self != nullptr);
@@ -1036,6 +1003,10 @@ ircd::ctx::continuation::continuation(const predicate &pred,
 	assert_critical();
 	assert(!critical_asserted);
 
+	// Confirming the uncaught exception count was saved and set to zero in the
+	// initializer list.
+	assert(!std::uncaught_exceptions());
+
 	// Note: Construct an instance of ctx::exception_handler to enable yielding
 	// in your catch block.
 	//
@@ -1057,15 +1028,6 @@ ircd::ctx::continuation::continuation(const predicate &pred,
 	// its execution run and is now yielding.
 	mark(prof::event::YIELD);
 
-	#ifdef HAVE_CXXABI_H
-	using __cxxabiv1::__cxa_get_globals_fast;
-	assert(__cxa_get_globals_fast());
-	assert(__cxa_get_globals_fast()->uncaughtExceptions == uncaught_exceptions);
-	__cxa_get_globals_fast()->uncaughtExceptions = 0;
-	#else
-	assert(!uncaught_exceptions);
-	#endif
-
 	// Check that we saved a valid context reference to this object for later.
 	assert(self->yc);
 
@@ -1097,16 +1059,9 @@ noexcept
 	// upon resuming execution.
 	ircd::ctx::current = self;
 
-	#ifdef HAVE_CXXABI_H
-	using __cxxabiv1::__cxa_get_globals_fast;
-	assert(__cxa_get_globals_fast());
-	assert(__cxa_get_globals_fast()->uncaughtExceptions == 0);
-	__cxa_get_globals_fast()->uncaughtExceptions = uncaught_exceptions;
-	assert(uint(std::uncaught_exceptions()) == uncaught_exceptions);
-	#else
+	// Restore the uncaught exception count for this context to the cxxabi
 	assert(std::uncaught_exceptions() == 0);
-	assert(uncaught_exceptions == 0);
-	#endif
+	exception_handler::uncaught_exceptions(uncaught_exceptions);
 
 	// Tell the profiler this is the point where the context is now resuming.
 	// On some optimized builds this might lead nowhere.

ircd/ctx_eh.cc

@@ -0,0 +1,120 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2019 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+#include <RB_INC_CXXABI_H
+#include <ircd/asio.h>
+#include "ctx.h"
+
+#ifdef HAVE_CXXABI_H
+struct __cxxabiv1::__cxa_eh_globals
+{
+	__cxa_exception *caughtExceptions;
+	unsigned int uncaughtExceptions;
+};
+#endif
+
+//
+// exception_handler
+//
+
+ircd::ctx::exception_handler::exception_handler()
+noexcept
+:std::exception_ptr
+{
+	// capture a shared reference of the current exception before the catch
+	// block closes around it.
+	std::current_exception()
+}
+{
+	assert(bool(*this));
+
+	// close the catch block.
+	end_catch();
+
+	// We don't yet support more levels of exceptions; after ending this
+	// catch we can't still be in another one. This doesn't apply if we're
+	// not on any ctx currently.
+	assert(!current || !std::uncaught_exceptions());
+}
+
+//
+// util
+//
+
+#ifdef HAVE_CXXABI_H
+void
+ircd::ctx::exception_handler::end_catch()
+noexcept
+{
+	if(likely(current))
+		__cxxabiv1::__cxa_end_catch();
+}
+#else
+#warning "CXXABI not available. Context switch inside catch block may be unsafe!"
+void
+ircd::ctx::exception_handler::end_catch()
+noexcept
+{
+}
+#endif
+
+#ifdef HAVE_CXXABI_H
+uint
+ircd::ctx::exception_handler::uncaught_exceptions()
+noexcept
+{
+	const auto &cxa_globals
+	{
+		__cxxabiv1::__cxa_get_globals_fast()
+	};
+
+	assert(cxa_globals);
+	return cxa_globals->uncaughtExceptions;
+}
+#else
+#warning "CXXABI not available. Context switch with uncaught exceptions may be unsafe!"
+uint
+ircd::ctx::exception_handler::uncaught_exceptions()
+noexcept
+{
+	return std::uncaught_exceptions();
+}
+#endif
+
+#ifdef HAVE_CXXABI_H
+uint
+ircd::ctx::exception_handler::uncaught_exceptions(const uint &val)
+noexcept
+{
+	const auto &cxa_globals
+	{
+		__cxxabiv1::__cxa_get_globals_fast()
+	};
+
+	assert(cxa_globals);
+	const auto ret
+	{
+		cxa_globals->uncaughtExceptions
+	};
+
+	assert(unsigned(ret) == unsigned(std::uncaught_exceptions()));
+	cxa_globals->uncaughtExceptions = val;
+	return ret;
+}
+#else
+#warning "CXXABI not available. Context switch with uncaught exceptions may be unsafe!"
+uint
+ircd::ctx::exception_handler::uncaught_exceptions(const uint &val)
+noexcept
+{
+	assert(std::uncaught_exceptions() == val);
+	return std::uncaught_exceptions();
+}
+#endif