Restore AmigaOS build and runtime support (#8660)

CMake/finders/FindSDL.cmake

@@ -0,0 +1,32 @@
+# Wrapper around CMake's bundled FindSDL module.
+#
+# The bundled module runs its own `find_package(Threads)` and appends
+# `CMAKE_THREAD_LIBS_INIT` to the SDL libraries. AmigaOS has no POSIX threads
+# library — SDL 1.2 uses native AmigaOS tasks — and `m68k-amigaos-g++` rejects
+# both `-pthread` and `-lpthreads`, so strip the thread flag back out.
+#
+# This has to live in a wrapper rather than at the call site because
+# dependencies built from source (notably SDL_audiolib) call `find_package(SDL)`
+# themselves and propagate the flag through their own link interface.
+
+include("${CMAKE_ROOT}/Modules/FindSDL.cmake")
+
+if(AMIGA)
+  foreach(_devilutionx_sdl_var SDL_LIBRARY SDL_LIBRARIES SDL_LIBRARY_TEMP)
+    if(${_devilutionx_sdl_var})
+      list(FILTER ${_devilutionx_sdl_var} EXCLUDE REGEX "pthread")
+    endif()
+  endforeach()
+  unset(_devilutionx_sdl_var)
+
+  # The module also bakes the thread flag into the imported target's link
+  # interface, which is what dependencies actually consume.
+  if(TARGET SDL::SDL)
+    get_target_property(_devilutionx_sdl_iface SDL::SDL INTERFACE_LINK_LIBRARIES)
+    if(_devilutionx_sdl_iface)
+      list(FILTER _devilutionx_sdl_iface EXCLUDE REGEX "pthread")
+      set_target_properties(SDL::SDL PROPERTIES INTERFACE_LINK_LIBRARIES "${_devilutionx_sdl_iface}")
+    endif()
+    unset(_devilutionx_sdl_iface)
+  endif()
+endif()

CMake/platforms/amiga.cmake

@@ -1,3 +1,5 @@
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/threads-stub")
+
 set(BUILD_TESTING OFF)
 set(ASAN OFF)
 set(UBSAN OFF)
@@ -8,9 +10,11 @@ set(SDL1_VIDEO_MODE_BPP 8)
 set(DEVILUTIONX_SYSTEM_BZIP2 OFF)
 set(DEVILUTIONX_SYSTEM_ZLIB OFF)
 
-# Lower the optimization level to O2 because there are issues with O3.
-set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -O2")
-set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O2")
+# Lower the optimization level to O1 because m68k-amigaos GCC miscompiles at
+# -O2 and above. See also the AMIGA branch in Source/CMakeLists.txt, which keeps
+# the rendering code from being bumped back up to -O2.
+set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -O1")
+set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O1")
 
 # `fseeko` fails to link on Amiga.
 add_definitions(-Dfseeko=fseek)

CMake/platforms/threads-stub/FindThreads.cmake

@@ -1,3 +1,6 @@
 # Stub out the Threads package.
 # Some platforms do not have a system threads library but SDL threads are supported.
-add_library(Threads::Threads INTERFACE IMPORTED GLOBAL)
+set(Threads_FOUND TRUE)
+if(NOT TARGET Threads::Threads)
+  add_library(Threads::Threads INTERFACE IMPORTED GLOBAL)
+endif()

CMakeLists.txt

@@ -274,7 +274,11 @@ endif()
 #
 # PS4 toolchain crashes in `create-fself` when linking with these flags, so we exclude it:
 # https://github.com/PacBrew/ps4-openorbis/issues/8
-if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND NOT PS4)
+# On m68k-amigaos, `--gc-sections` discards static constexpr data that is still
+# referenced (magic_enum's per-enum name tables are the visible casualty: the
+# string_views survive with correct lengths but point at collected storage, so
+# every enum name reads as garbage). Excluded here for the same reason as PS4.
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND NOT PS4 AND NOT AMIGA)
   add_compile_options("$<$<NOT:$<CONFIG:Debug>>:-ffunction-sections;-fdata-sections>")
   if(APPLE)
     add_link_options("$<$<NOT:$<CONFIG:Debug>>:LINKER:-dead_strip>")

Source/CMakeLists.txt

@@ -174,7 +174,12 @@ set(_optimize_in_debug_srcs
   utils/cel_to_clx.cpp
   utils/cl2_to_clx.cpp
   utils/pcx_to_clx.cpp)
-if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+# These COMPILE_OPTIONS are appended after the global flags, so on Amiga they
+# would otherwise override the -O1 set in CMake/platforms/amiga.cmake. m68k-amigaos
+# GCC miscompiles this rendering code at -O2.
+if(AMIGA)
+  set_source_files_properties(${_optimize_in_debug_srcs} PROPERTIES COMPILE_OPTIONS "-O1;--param=max-vartrack-size=900000000")
+elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   set_source_files_properties(${_optimize_in_debug_srcs} PROPERTIES COMPILE_OPTIONS "-O2;--param=max-vartrack-size=900000000")
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
   set_source_files_properties(${_optimize_in_debug_srcs} PROPERTIES COMPILE_OPTIONS "-O2")
@@ -890,6 +895,8 @@ endif()
 if(AMIGA AND NOT WARPOS)
   # Works around a missing `__cmpdf2` in the hard-float libgcc multilib.
   list(APPEND libdevilutionx_SRCS platform/amiga/cmpdf2.c)
+  # Works around a missing `__xpg_strerror_r` under GCC 15's libstdc++.
+  list(APPEND libdevilutionx_SRCS platform/amiga/strerror_r.c)
 endif()
 
 if(NOT DISABLE_DEMOMODE)

Source/engine/random.hpp

@@ -272,7 +272,10 @@ private:
 	{
 		seed(timeSeed());
 
-#if !(defined(WINVER) && WINVER <= 0x0500 && (!defined(_WIN32_WINNT) || _WIN32_WINNT == 0))
+// AmigaOS has no entropy source backing std::random_device; constructing it
+// aborts, and this runs during static initialization, so the process dies
+// before main().
+#if !(defined(WINVER) && WINVER <= 0x0500 && (!defined(_WIN32_WINNT) || _WIN32_WINNT == 0)) && !defined(__amigaos__)
 		static std::random_device rd;
 		std::uniform_int_distribution<uint32_t> dist;
 		for (uint32_t &cell : s)

Source/platform/amiga/strerror_r.c

@@ -0,0 +1,30 @@
+/*
+ * GCC 15's libstdc++ (system_error.o) calls the XSI-compliant `strerror_r`,
+ * but libnix only ships the GNU-flavoured one, so linking fails with an
+ * undefined `__xpg_strerror_r`.
+ */
+#include <errno.h>
+#include <stddef.h>
+#include <string.h>
+
+int __xpg_strerror_r(int errnum, char *buf, size_t buflen);
+
+int __xpg_strerror_r(int errnum, char *buf, size_t buflen)
+{
+	if (buf == NULL || buflen == 0)
+		return ERANGE;
+
+	const char *msg = strerror(errnum);
+	if (msg == NULL)
+		return EINVAL;
+
+	const size_t len = strlen(msg);
+	if (len >= buflen) {
+		memcpy(buf, msg, buflen - 1);
+		buf[buflen - 1] = '\0';
+		return ERANGE;
+	}
+
+	memcpy(buf, msg, len + 1);
+	return 0;
+}

Source/utils/stdcompat/filesystem.hpp

@@ -6,7 +6,11 @@
     || (defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED < 130000)
 #define DVL_NO_FILESYSTEM
 #endif
-#elif defined(NXDK) || (defined(_MSVC_LANG) && _MSVC_LANG < 201703L) \
+// AmigaOS paths are not POSIX paths: volumes and assigns such as `PROGDIR:` or
+// `Work:games` use a colon that std::filesystem treats as an ordinary character,
+// so it fails to create or resolve them. The non-filesystem fallbacks below
+// handle these paths correctly.
+#elif defined(NXDK) || defined(__amigaos__) || (defined(_MSVC_LANG) && _MSVC_LANG < 201703L) \
     || (defined(WINVER) && WINVER <= 0x0500 && (!defined(_WIN32_WINNT) || _WIN32_WINNT == 0))
 #define DVL_NO_FILESYSTEM
 #endif