Add SDL_MIXER feature for conditional audio mixing

This introduces ENABLE_SDL_MIXER feature flag to conditionally compile
SDL2_mixer-dependent audio code. This allows SDL2 graphics support
without the problematic SDL2_mixer library in emscripten builds.

emscripten-ports/SDL2_mixer (archived in 2024) has unfixable compilation
warnings in music_modplug.c. The port system enforces -sSTRICT -Werror
which cannot be overridden.

Author: jserv

.github/workflows/main.yml

@@ -283,8 +283,14 @@ jobs:
     - name: Architecture test
       env:
         CC: ${{ steps.install_cc.outputs.cc }}
-        LATEST_RELEASE: dummy
       run: |
+            . .ci/common.sh
+            export LATEST_RELEASE=$(download_with_headers "https://api.github.com/repos/sysprog21/rv32emu-prebuilt/releases" \
+                                                          "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}" \
+                                           | grep '"tag_name"' \
+                                           | grep "sail" \
+                                           | head -n 1 \
+                                           | sed -E 's/.*"tag_name": "([^"]+)".*/\1/')
             .ci/riscv-tests.sh
       if: ${{ always() }}
 
@@ -342,7 +348,11 @@ jobs:
      - uses: actions/checkout@v4
      - name: install-dependencies
        run: |
-             brew install make dtc expect sdl2 sdl2_mixer bc e2fsprogs p7zip llvm@18 dcfldd
+             brew install make dtc expect sdl2 bc e2fsprogs p7zip llvm@18 dcfldd
+             brew install sdl2_mixer || {
+               echo "Warning: sdl2_mixer installation failed, continuing without SDL_MIXER support"
+               echo "ENABLE_SDL_MIXER=0" >> $GITHUB_ENV
+             }
              .ci/riscv-toolchain-install.sh
              echo "${{ github.workspace }}/toolchain/bin" >> $GITHUB_PATH
              echo "$(brew --prefix llvm@18)/bin" >> $GITHUB_PATH
@@ -489,8 +499,14 @@ jobs:
      - name: Architecture test
        env:
          CC: ${{ steps.install_cc.outputs.cc }}
-         LATEST_RELEASE: dummy
        run: |
+             . .ci/common.sh
+             export LATEST_RELEASE=$(download_with_headers "https://api.github.com/repos/sysprog21/rv32emu-prebuilt/releases" \
+                                                           "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}" \
+                                            | grep '"tag_name"' \
+                                            | grep "sail" \
+                                            | head -n 1 \
+                                            | sed -E 's/.*"tag_name": "([^"]+)".*/\1/')
              python3 -m venv venv
              . venv/bin/activate
              .ci/riscv-tests.sh

Makefile

@@ -199,27 +199,58 @@ ENABLE_FULL4G ?= 0
 
 # Experimental SDL oriented system calls
 ENABLE_SDL ?= 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 (, $(shell which sdl2-config))
+ENABLE_SDL_MIXER ?= 1
+
+# Step 1: Detect SDL availability
+ifneq ("$(CC_IS_EMCC)", "1")
+# Native build: require sdl2-config for SDL support
+ifeq (, $(shell command -v sdl2-config))
 $(warning No sdl2-config in $$PATH. Check SDL2 installation in advance)
 override ENABLE_SDL := 0
+override ENABLE_SDL_MIXER := 0
+endif
+else
+# Emscripten build: SDL is available via ports, but SDL_MIXER has unfixable warnings
+# The emscripten-ports/SDL2_mixer was archived in Jan 2024 with compilation issues
+override ENABLE_SDL_MIXER := 0
+endif
+
+# Enforce dependency: SDL_MIXER requires SDL
+ifeq ($(ENABLE_SDL), 0)
+override ENABLE_SDL_MIXER := 0
+endif
+
+# Step 2: If SDL is enabled on native builds, check for SDL_MIXER
+ifneq ("$(CC_IS_EMCC)", "1")
+ifeq ($(ENABLE_SDL), 1)
+ifneq (, $(shell command -v pkg-config))
+ifneq (0, $(shell pkg-config --exists SDL2_mixer; echo $$?))
+$(warning No SDL2_mixer lib installed. SDL2_mixer support will be disabled)
+override ENABLE_SDL_MIXER := 0
+endif
+else
+$(warning No pkg-config found. Disabling SDL2_mixer support)
+override ENABLE_SDL_MIXER := 0
 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
 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

@@ -18,12 +18,15 @@ CFLAGS += -mtail-call
 
 # Build emscripten-port SDL
 ifeq ($(call has, SDL), 1)
-# Disable STRICT mode to avoid -Werror in SDL2_mixer port compilation.
-# The emscripten-ports/SDL2_mixer was archived in Jan 2024 and has warnings
-# in music_modplug.c that become fatal errors under STRICT mode.
-CFLAGS_emcc += -sSTRICT=0 -sUSE_SDL=2 -sSDL2_MIXER_FORMATS=wav,mid -sUSE_SDL_MIXER=2
+CFLAGS_emcc += -sUSE_SDL=2
 OBJS_EXT += syscall_sdl.o
 LDFLAGS += -pthread
+# SDL_MIXER is disabled by default for emscripten due to archived port with warnings
+ifeq ($(call has, SDL_MIXER), 1)
+# Note: Enabling SDL_MIXER requires -sSTRICT=0 due to unfixable warnings in music_modplug.c
+# The emscripten-ports/SDL2_mixer was archived in Jan 2024
+CFLAGS_emcc += -sSTRICT=0 -sSDL2_MIXER_FORMATS=wav,mid -sUSE_SDL_MIXER=2
+endif
 endif
 
 # More build flags

src/feature.h

@@ -67,6 +67,17 @@
 #define RV32_FEATURE_SDL 1
 #endif
 
+/* SDL2_mixer audio support (requires SDL) */
+#ifndef RV32_FEATURE_SDL_MIXER
+#define RV32_FEATURE_SDL_MIXER 1
+#endif
+
+/* Enforce dependency: SDL_MIXER requires SDL */
+#if RV32_FEATURE_SDL_MIXER && !RV32_FEATURE_SDL
+#undef RV32_FEATURE_SDL_MIXER
+#define RV32_FEATURE_SDL_MIXER 0
+#endif
+
 /* GDB remote debugging */
 #ifndef RV32_FEATURE_GDBSTUB
 #define RV32_FEATURE_GDBSTUB 0

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"
@@ -92,6 +94,7 @@ typedef struct sound {
 } sound_t;
 
 /* SDL-mixer-related and music-related variables */
+#if RV32_HAS(SDL_MIXER)
 static pthread_t music_thread;
 static uint8_t *music_midi_data;
 static Mix_Music *mid;
@@ -107,6 +110,7 @@ static int chan;
 static bool audio_init = false;
 static bool sfx_thread_init = false;
 static bool music_thread_init = false;
+#endif
 
 typedef struct {
     void *data;
@@ -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;
@@ -916,7 +921,9 @@ 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) */
 
+#if RV32_HAS(SDL_MIXER)
 static void init_audio(void)
 {
     if (!(SDL_WasInit(-1) & SDL_INIT_AUDIO)) {
@@ -977,13 +984,16 @@ static void shutdown_audio()
 
     audio_init = sfx_thread_init = music_thread_init = false;
 }
+#endif
 
 void sdl_video_audio_cleanup()
 {
     if (window) {
         SDL_DestroyWindow(window);
         window = NULL;
     }
+
+#if RV32_HAS(SDL_MIXER)
     /*
      * The sfx_or_music_thread_init flag might not be set if a quick ctrl-c
      * occurs while the audio configuration is being initialized. Therefore,
@@ -992,6 +1002,7 @@ void sdl_video_audio_cleanup()
     bool sfx_or_music_thread_init = sfx_thread_init | music_thread_init;
     if (sfx_or_music_thread_init || (!sfx_or_music_thread_init && audio_init))
         shutdown_audio();
+#endif
     SDL_Quit();
 }
 
@@ -1002,10 +1013,14 @@ void syscall_setup_audio(riscv_t *rv)
 
     switch (request) {
     case INIT_AUDIO:
+#if RV32_HAS(SDL_MIXER)
         init_audio();
+#endif
         break;
     case SHUTDOWN_AUDIO:
+#if RV32_HAS(SDL_MIXER)
         shutdown_audio();
+#endif
         break;
     default:
         rv_log_error("Unknown sound request: %d", request);
@@ -1020,16 +1035,24 @@ 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);