Add SDL_MIXER flag to conditionally compile

This fixes emscripten build failures by introducing ENABLE_SDL_MIXER
feature flag to conditionally compile SDL2_mixer-dependent code. This
allows SDL2 graphics support without the problematic SDL2_mixer audio
library.

Author: jserv

Makefile

@@ -1,9 +1,9 @@
 include mk/common.mk
 include mk/toolchain.mk
 
-# Verify GNU make version (3.80+ required for order-only prerequisites)
-ifeq ($(filter 3.80 3.81 3.82 3.83 3.84 4.% 5.%,$(MAKE_VERSION)),)
-$(error GNU make 3.80 or higher is required. Current version: $(MAKE_VERSION))
+# Verify GNU make version (3.81+ required for $(info) function and order-only prerequisites)
+ifeq ($(filter 3.81 3.82 3.83 3.84 4.% 5.%,$(MAKE_VERSION)),)
+$(error GNU make 3.81 or higher is required. Current version: $(MAKE_VERSION))
 endif
 
 OUT ?= build
@@ -180,6 +180,7 @@ ENABLE_FULL4G ?= 0
 
 # Experimental SDL oriented system calls
 ENABLE_SDL ?= 1
+ENABLE_SDL_MIXER ?= 1
 ifneq ("$(CC_IS_EMCC)", "1") # note that emcc generates port SDL headers/library, so it does not requires system SDL headers/library
 ifeq ($(call has, SDL), 1)
 ifeq (, $(shell which sdl2-config))
@@ -189,18 +190,26 @@ endif
 ifeq (1, $(shell pkg-config --exists SDL2_mixer; echo $$?))
 $(warning No SDL2_mixer lib installed. Check SDL2_mixer installation in advance)
 override ENABLE_SDL := 0
+override ENABLE_SDL_MIXER := 0
+endif
 endif
 endif
 $(call set-feature, SDL)
+$(call set-feature, SDL_MIXER)
 ifeq ($(call has, SDL), 1)
 OBJS_EXT += syscall_sdl.o
+ifneq ("$(CC_IS_EMCC)", "1")
 $(OUT)/syscall_sdl.o: CFLAGS += $(shell sdl2-config --cflags)
+endif
 # 4 GiB of memory is required to run video games.
 ENABLE_FULL4G := 1
+ifneq ("$(CC_IS_EMCC)", "1")
 LDFLAGS += $(shell sdl2-config --libs) -pthread
+ifeq ($(call has, SDL_MIXER), 1)
 LDFLAGS += $(shell pkg-config --libs SDL2_mixer)
 endif
 endif
+endif
 
 # If SYSTEM is enabled and ELF_LOADER is not, then skip FULL4G bacause guestOS
 # has dedicated memory mapping range.

mk/wasm.mk

@@ -16,13 +16,14 @@ BIN := $(BIN).js
 # TCO
 CFLAGS += -mtail-call
 
+# Disable SDL_mixer for emscripten builds
+# The emscripten-ports/SDL2_mixer repository was archived in Jan 2024 and has
+# unfixable compilation warnings. The port system internally enforces -sSTRICT
+# -Werror which cannot be overridden. Games (Doom/Quake) work without audio mixing.
+override ENABLE_SDL_MIXER := 0
+
 # Build emscripten-port SDL
 ifeq ($(call has, SDL), 1)
-# NOTE: SDL2_mixer is disabled for emscripten builds because:
-# 1. The emscripten-ports/SDL2_mixer repository was archived in Jan 2024
-# 2. It has unfixable compilation warnings in music_modplug.c
-# 3. The port system internally enforces -sSTRICT -Werror which cannot be overridden
-# 4. Games (Doom/Quake) work without audio mixing, SDL2 alone provides graphics
 CFLAGS_emcc += -sUSE_SDL=2
 OBJS_EXT += syscall_sdl.o
 LDFLAGS += -pthread

src/syscall_sdl.c

@@ -15,7 +15,9 @@
 #include <unistd.h>
 
 #include <SDL.h>
+#if RV32_HAS(SDL_MIXER)
 #include <SDL_mixer.h>
+#endif
 
 #include "riscv.h"
 #include "riscv_private.h"
@@ -94,11 +96,13 @@ typedef struct sound {
 /* SDL-mixer-related and music-related variables */
 static pthread_t music_thread;
 static uint8_t *music_midi_data;
+#if RV32_HAS(SDL_MIXER)
 static Mix_Music *mid;
 
 /* SDL-mixer-related and sfx-related variables */
 static pthread_t sfx_thread;
 static Mix_Chunk *sfx_chunk;
+#endif
 static uint8_t *sfx_samples;
 static uint32_t nr_sfx_samples;
 static int chan;
@@ -718,6 +722,7 @@ uint8_t *mus2midi(uint8_t *data, int *length)
     return midi_data;
 }
 
+#if RV32_HAS(SDL_MIXER)
 static void *sfx_handler(void *arg)
 {
     sound_t *sfx = (sound_t *) arg;
@@ -836,8 +841,10 @@ static void play_sfx(riscv_t *rv)
         .size = sfx_data_size,
         .volume = volume,
     };
+#if RV32_HAS(SDL_MIXER)
     pthread_create(&sfx_thread, NULL, sfx_handler, &sfx);
     sfx_thread_init = true;
+#endif
     /* FIXME: In web browser runtime, web workers in thread pool do not reap
      * after sfx_handler return, thus we have to join them. sfx_handler does not
      * contain infinite loop,so do not worry to be stalled by it */
@@ -893,8 +900,10 @@ static void play_music(riscv_t *rv)
         .looping = looping,
         .volume = volume,
     };
+#if RV32_HAS(SDL_MIXER)
     pthread_create(&music_thread, NULL, music_handler, &music);
     music_thread_init = true;
+#endif
     /* FIXME: In web browser runtime, web workers in thread pool do not reap
      * after music_handler return, thus we have to join them. music_handler does
      * not contain infinite loop,so do not worry to be stalled by it */
@@ -916,6 +925,7 @@ static void set_music_volume(riscv_t *rv)
     /* multiplied by 8 because volume's max is 15 */
     Mix_VolumeMusic(volume * 8);
 }
+#endif /* RV32_HAS(SDL_MIXER) */
 
 static void init_audio(void)
 {
@@ -933,6 +943,7 @@ static void init_audio(void)
         exit(EXIT_FAILURE);
     }
 
+#if RV32_HAS(SDL_MIXER)
     /* Initialize SDL2 Mixer */
     if (Mix_Init(MIX_INIT_MID) != MIX_INIT_MID) {
         rv_log_fatal("Mix_Init failed: %s", Mix_GetError());
@@ -943,6 +954,7 @@ static void init_audio(void)
         Mix_Quit();
         exit(EXIT_FAILURE);
     }
+#endif
     audio_init = true;
 }
 
@@ -956,6 +968,7 @@ static void shutdown_audio()
      * on a valid pthread_t identifier.
      */
 
+#if RV32_HAS(SDL_MIXER)
     if (music_thread_init) {
         stop_music();
         pthread_join(music_thread, NULL);
@@ -974,6 +987,7 @@ static void shutdown_audio()
 
     Mix_CloseAudio();
     Mix_Quit();
+#endif
 
     audio_init = sfx_thread_init = music_thread_init = false;
 }
@@ -1020,16 +1034,24 @@ void syscall_control_audio(riscv_t *rv)
 
     switch (request) {
     case PLAY_MUSIC:
+#if RV32_HAS(SDL_MIXER)
         play_music(rv);
+#endif
         break;
     case PLAY_SFX:
+#if RV32_HAS(SDL_MIXER)
         play_sfx(rv);
+#endif
         break;
     case SET_MUSIC_VOLUME:
+#if RV32_HAS(SDL_MIXER)
         set_music_volume(rv);
+#endif
         break;
     case STOP_MUSIC:
+#if RV32_HAS(SDL_MIXER)
         stop_music();
+#endif
         break;
     default:
         rv_log_error("Unknown sound control request: %d", request);