Prevent segfaults due to audio buffer overflows

libgambatte/include/gambatte.h

@@ -54,6 +54,8 @@ public:
 	  *
 	  * There are 35112 stereo sound samples in a video frame.
 	  * May run for uptil 2064 stereo samples too long.
+	  * EDIT: Due to internal emulator bugs, may in fact run for
+	  *       an arbitrary number of samples...
 	  * A stereo sample consists of two native endian 2s complement 16-bit PCM samples,
 	  * with the left sample preceding the right one. Usually casting soundBuf to/from
 	  * short* is OK and recommended. The reason for not using a short* in the interface
@@ -67,11 +69,12 @@ public:
 	  * @param videoBuf 160x144 RGB32 (native endian) video frame buffer or 0
 	  * @param pitch distance in number of pixels (not bytes) from the start of one line to the next in videoBuf.
 	  * @param soundBuf buffer with space >= samples + 2064
+	  * @param soundBufSize actual size of soundBuf buffer
 	  * @param samples in: number of stereo samples to produce, out: actual number of samples produced
 	  * @return sample number at which the video frame was produced. -1 means no frame was produced.
 	  */
 	long runFor(gambatte::video_pixel_t *videoBuf, int pitch,
-			gambatte::uint_least32_t *soundBuf, unsigned &samples);
+			gambatte::uint_least32_t *soundBuf, std::size_t soundBufSize, unsigned &samples);
 	
 	/** Reset to initial state.
 	  * Equivalent to reloading a ROM image, or turning a Game Boy Color off and on again.

libgambatte/libretro/libretro.cpp

@@ -90,6 +90,21 @@ bool use_official_bootloader = false;
 #define VIDEO_BUFF_SIZE (256 * NUM_GAMEBOYS * VIDEO_HEIGHT * sizeof(gambatte::video_pixel_t))
 #define VIDEO_PITCH (256 * NUM_GAMEBOYS)
 
+/* There are 35112 stereo sound samples in a video frame */
+#define SOUND_SAMPLES_PER_FRAME 35112
+/* We request 2064 samples from each call of GB::runFor() */
+#define SOUND_SAMPLES_PER_RUN   2064
+/* GB::runFor() nominally generates up to
+ * (SOUND_SAMPLES_PER_RUN + 2064) samples, which
+ * defines our sound buffer size
+ * NOTE: This is in fact a lie - in the upstream code,
+ * GB::runFor() can generate more than
+ * (SOUND_SAMPLES_PER_RUN + 2064) samples, causing a
+ * buffer overflow. It has been necessary to add an
+ * internal hard cap/bail out in the event that
+ * excess samples are detected... */
+#define SOUND_BUFF_SIZE         (SOUND_SAMPLES_PER_RUN + 2064)
+
 /*****************************/
 /* Interframe blending START */
 /*****************************/
@@ -903,7 +918,7 @@ void retro_init(void)
 #endif
 
    double fps = 4194304.0 / 70224.0;
-   double sample_rate = fps * 35112;
+   double sample_rate = fps * SOUND_SAMPLES_PER_FRAME;
 
 #ifdef CC_RESAMPLER
    CC_init();
@@ -1825,7 +1840,7 @@ void retro_run()
    input_poll_cb();
    update_input_state();
 
-   uint64_t expected_frames = samples_count / 35112;
+   uint64_t expected_frames = samples_count / SOUND_SAMPLES_PER_FRAME;
    if (frames_count < expected_frames) // Detect frame dupes.
    {
       video_cb(NULL, VIDEO_WIDTH, VIDEO_HEIGHT, VIDEO_PITCH * sizeof(gambatte::video_pixel_t));
@@ -1835,12 +1850,12 @@ void retro_run()
 
    union
    {
-      gambatte::uint_least32_t u32[2064 + 2064];
+      gambatte::uint_least32_t u32[SOUND_BUFF_SIZE];
-      int16_t i16[2 * (2064 + 2064)];
+      int16_t i16[2 * SOUND_BUFF_SIZE];
    } static sound_buf;
-   unsigned samples = 2064;
+   unsigned samples = SOUND_SAMPLES_PER_RUN;
 
-   while (gb.runFor(video_buf, VIDEO_PITCH, sound_buf.u32, samples) == -1)
+   while (gb.runFor(video_buf, VIDEO_PITCH, sound_buf.u32, SOUND_BUFF_SIZE, samples) == -1)
    {
 #ifdef CC_RESAMPLER
       CC_renderaudio((audio_frame_t*)sound_buf.u32, samples);
@@ -1857,7 +1872,7 @@ void retro_run()
 
 #endif
       samples_count += samples;
-      samples = 2064;
+      samples = SOUND_SAMPLES_PER_RUN;
    }
 #ifdef DUAL_MODE
    while (gb2.runFor(video_buf + GB_SCREEN_WIDTH, VIDEO_PITCH, sound_buf.u32, samples) == -1) {}

libgambatte/src/cpu.h

@@ -86,7 +86,7 @@ public:
 #if 0
 	bool loaded() const { return mem_.loaded(); }
 #endif
-	void setSoundBuffer(uint_least32_t *buf) { mem_.setSoundBuffer(buf); }
+	void setSoundBuffer(uint_least32_t *buf, std::size_t size) { mem_.setSoundBuffer(buf, size); }
 	std::size_t fillSoundBuffer() { return mem_.fillSoundBuffer(cycleCounter_); }
 	bool isCgb() const { return mem_.isCgb(); }
 

libgambatte/src/gambatte-memory.h

@@ -120,7 +120,7 @@ public:
 	void setSerialIO(SerialIO* serial_io) { serial_io_ = serial_io; }
 #endif
 	void setEndtime(unsigned long cc, unsigned long inc);
-	void setSoundBuffer(uint_least32_t *buf) { psg_.setBuffer(buf); }
+	void setSoundBuffer(uint_least32_t *buf, std::size_t size) { psg_.setBuffer(buf, size); }
 	std::size_t fillSoundBuffer(unsigned long cc);
 
 	void setVideoBuffer(video_pixel_t *videoBuf, std::ptrdiff_t pitch) {

libgambatte/src/gambatte.cpp

@@ -43,10 +43,10 @@ GB::~GB() {
 }
 
 long GB::runFor(gambatte::video_pixel_t *const videoBuf, const int pitch,
-			gambatte::uint_least32_t *const soundBuf, unsigned &samples) {
+			gambatte::uint_least32_t *const soundBuf, std::size_t soundBufSize, unsigned &samples) {
 	
 	p_->cpu.setVideoBuffer(videoBuf, pitch);
-	p_->cpu.setSoundBuffer(soundBuf);
+	p_->cpu.setSoundBuffer(soundBuf, soundBufSize);
 	const long cyclesSinceBlit = p_->cpu.runFor(samples * 2);
 	samples = p_->cpu.fillSoundBuffer();
 	

libgambatte/src/sound.cpp

@@ -45,6 +45,7 @@ namespace gambatte
 
    PSG::PSG()
       :  buffer_(0)
+      ,  bufferSize_(0)
       ,  bufferPos_(0)
       ,  lastUpdate_(0)
       ,  soVol_(0)
@@ -96,7 +97,6 @@ namespace gambatte
    void PSG::accumulateChannels(const unsigned long cycles)
    {
       uint_least32_t *const buf = buffer_ + bufferPos_;
-
       std::memset(buf, 0, cycles * sizeof(uint_least32_t));
       ch1_.update(buf, soVol_, cycles);
       ch2_.update(buf, soVol_, cycles);
@@ -106,7 +106,11 @@ namespace gambatte
 
    void PSG::generateSamples(unsigned long const cycleCounter, bool const doubleSpeed)
    {
-      unsigned long const cycles = (cycleCounter - lastUpdate_) >> (1 + doubleSpeed);
+      unsigned long cycles = (cycleCounter - lastUpdate_) >> (1 + doubleSpeed);
+
+      if (cycles + bufferPos_ > bufferSize_)
+         cycles = (bufferSize_ > bufferPos_) ? (bufferSize_ - bufferPos_) : 0;
+
       lastUpdate_ += cycles << (1 + doubleSpeed);
 
       if (cycles)

libgambatte/src/sound.h

@@ -41,7 +41,7 @@ public:
 	void generateSamples(unsigned long cycleCounter, bool doubleSpeed);
 	void resetCounter(unsigned long newCc, unsigned long oldCc, bool doubleSpeed);
    std::size_t fillBuffer();
-	void setBuffer(uint_least32_t *buf) { buffer_ = buf; bufferPos_ = 0; }
+	void setBuffer(uint_least32_t *buf, std::size_t size) { buffer_ = buf; bufferSize_ = size; bufferPos_ = 0; }
 
 	bool isEnabled() const { return enabled_; }
 	void setEnabled(bool value) { enabled_ = value; }
@@ -80,6 +80,7 @@ private:
 	Channel3 ch3_;
 	Channel4 ch4_;
 	uint_least32_t *buffer_;
+	std::size_t bufferSize_;
 	std::size_t bufferPos_;
 	unsigned long lastUpdate_;
 	unsigned long soVol_;