Potential very hacky workaround for arm64 JIT allocation issues.

Try to reserve blocks of executable memory before external library code claims the address space. LuaJIT on arm64 currently has a very limited range of memory it can use for JIT code.

src/modules/love/jitsetup.lua

@@ -0,0 +1,71 @@
+R"luastring"--(
+-- DO NOT REMOVE THE ABOVE LINE. It is used to load this file as a C++ string.
+-- There is a matching delimiter at the bottom of the file.
+
+--[[
+Copyright (c) 2006-2021 LOVE Development Team
+
+This software is provided 'as-is', without any express or implied
+warranty.  In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
+   in a product, an acknowledgment in the product documentation would be
+   appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be
+   misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+--]]
+
+if type(jit) ~= "table" or not jit.status() then
+	return
+end
+
+-- Double the defaults.
+jit.opt.start("maxtrace=2000", "maxrecord=8000")
+
+-- Somewhat arbitrary value. Needs to be higher than the combined sizes below,
+-- and higher than the default (512) because that's already too low.
+jit.opt.start("maxmcode=16384")
+
+if jit.arch == "arm64" then
+	-- https://github.com/LuaJIT/LuaJIT/issues/285
+	-- LuaJIT 2.1 on arm64 currently (as of commit b4b2dce) can only use memory
+	-- for JIT compilation within a certain short range. Other libraries such as
+	-- SDL can take all the usable space in that range and cause attempts at JIT
+	-- compilation to both fail and take a long time.
+	-- This is a very hacky attempt at a workaround. LuaJIT allocates executable
+	-- code in pools. We'll try "reserving" pools before any external code is
+	-- executed, by causing JIT compilation via a small loop. We can't easily
+	-- tell if JIT compilation succeeded, so we do several successively smaller
+	-- pool allocations in case previous ones fail.
+	-- This is a really hacky hack and by no means foolproof - there are a lot of
+	-- potential situations (especially when threads are used) where previously
+	-- executed external code will still take up space that LuaJIT needed for itself.
+
+	jit.opt.start("sizemcode=2048")
+	for i=1, 100 do end
+	
+	jit.opt.start("sizemcode=1024")
+	for i=1, 100 do end
+	
+	jit.opt.start("sizemcode=512")
+	for i=1, 100 do end
+	
+	jit.opt.start("sizemcode=256")
+	for i=1, 100 do end
+	
+	jit.opt.start("sizemcode=128")
+	for i=1, 100 do end
+else
+	-- Somewhat arbitrary value (>= the default).
+	jit.opt.start("sizemcode=128")
+end
+
+-- DO NOT REMOVE THE NEXT LINE. It is used to load this file as a C++ string.
+--)luastring"--"

src/modules/love/love.cpp

@@ -97,6 +97,10 @@ static const char boot_lua[] =
 #include "boot.lua"
 ;
 
+static const char jit_setup_lua[] =
+#include "jitsetup.lua"
+;
+
 // All modules define a c-accessible luaopen
 // so let's make use of those, instead
 // of addressing implementations directly.
@@ -160,6 +164,7 @@ extern "C"
 	extern int luaopen_love_window(lua_State*);
 #endif
 	extern int luaopen_love_nogame(lua_State*);
+	extern int luaopen_love_jitsetup(lua_State*);
 	extern int luaopen_love_arg(lua_State*);
 	extern int luaopen_love_callbacks(lua_State*);
 	extern int luaopen_love_boot(lua_State*);
@@ -224,6 +229,7 @@ static const luaL_Reg modules[] = {
 	{ "love.window", luaopen_love_window },
 #endif
 	{ "love.nogame", luaopen_love_nogame },
+	{ "love.jitsetup", luaopen_love_jitsetup },
 	{ "love.arg", luaopen_love_arg },
 	{ "love.callbacks", luaopen_love_callbacks },
 	{ "love.boot", luaopen_love_boot },
@@ -404,6 +410,15 @@ static void luax_addcompatibilityalias(lua_State *L, const char *module, const c
 
 int luaopen_love(lua_State *L)
 {
+	// Preload module loaders.
+	for (int i = 0; modules[i].name != nullptr; i++)
+		love::luax_preload(L, modules[i].func, modules[i].name);
+
+	// jitsetup is also loaded in the love executable runlove function. It's
+	// needed here too for threads. Note that it doesn't use the love table.
+	love::luax_require(L, "love.jitsetup");
+	lua_pop(L, 1);
+
 	love::luax_insistpinnedthread(L);
 
 	love::luax_insistglobal(L, "love");
@@ -501,10 +516,6 @@ int luaopen_love(lua_State *L)
 		lua_setfield(L, -2, "hasDeprecationOutput");
 	}
 
-	// Preload module loaders.
-	for (int i = 0; modules[i].name != nullptr; i++)
-		love::luax_preload(L, modules[i].func, modules[i].name);
-
 	// Necessary for Data-creating methods to work properly in Data subclasses.
 	love::luax_require(L, "love.data");
 	lua_pop(L, 1);
@@ -657,6 +668,14 @@ int luaopen_love_nogame(lua_State *L)
 	return 1;
 }
 
+int luaopen_love_jitsetup(lua_State *L)
+{
+	if (luaL_loadbuffer(L, jit_setup_lua, sizeof(jit_setup_lua), "jitsetup.lua") == 0)
+		lua_call(L, 0, 1);
+
+	return 1;
+}
+
 int luaopen_love_arg(lua_State *L)
 {
 	if (luaL_loadbuffer(L, arg_lua, sizeof(arg_lua), "arg.lua") == 0)

src/modules/love/love.h

@@ -36,6 +36,9 @@ LOVE_EXPORT const char *love_version();
 LOVE_EXPORT const char *love_codename();
 LOVE_EXPORT int luaopen_love(lua_State *L);
 LOVE_EXPORT int luaopen_love_nogame(lua_State *L);
+LOVE_EXPORT int luaopen_love_jitsetup(lua_State *L);
+LOVE_EXPORT int luaopen_love_arg(lua_State *L);
+LOVE_EXPORT int luaopen_love_callbacks(lua_State *L);
 LOVE_EXPORT int luaopen_love_boot(lua_State *L);
 
 #ifdef LOVE_LEGENDARY_CONSOLE_IO_HACK