fix(libretro): expose the Memory Track as SAVE_RAM on no-content boot (#810)

A no-content session never exposed SAVE_RAM (no_game_active), so Memory
Track writes made through a disc inserted via disk control were never
handed to the frontend. Two causes:

1. SAVE_RAM was gated on no_game_active, a #646-era rule ("no cartridge,
   no EEPROM"). #726 made no-content boot a CD session with the Memory
   Track plugged in from frame 0, so the gate is stale. It now follows
   jaguarMemTrackInserted. It is deliberately not keyed on a mounted
   disc: frontends size and load SAVE_RAM once after retro_load_game and
   libretro has no change notification, so exposing it first after an
   insert would write a file that is never read back.
2. The insert path never reinstalled the NVM BIOS module. The boot resets
   RAM, wiping the '_NVM' cookie; retro_load_game and retro_reset
   reinstall it, disk_set_eject_state did not. Found by the new test.

Tests: test_disk_control cases 6/7/8; test_boot_config's #646 size-0
assertion becomes the new contract. mtMem joins the test export lists.
No savestate change.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

Makefile

@@ -2086,6 +2086,11 @@ test: test/test_dram_timing test/test_cheat test/test_event_queue test/test_jlin
 	@# in the `if [ -n "$$disc" ]` block, where it silently ran nowhere but
 	@# a corpus machine.
 	./test/tools/test_disk_control ./$(TARGET) --case 5 --quiet
+	@# Case 6 (#810): the Memory Track is exposed as SAVE_RAM from the first
+	@# query of a no-content boot, and a frontend-loaded .srm reaches mtMem.
+	@# Also disc-free, so it stays outside the corpus guard for the same
+	@# reason as case 5.
+	./test/tools/test_disk_control ./$(TARGET) --case 6 --quiet
 
 	@# Baldies HLE cutscene (#738): the boot classifier PASSED this title
 	@# while it was frozen from frame ~600 (it reaches game code and is
@@ -2113,6 +2118,8 @@ test: test/test_dram_timing test/test_cheat test/test_event_queue test/test_jlin
 		rc=0; \
 		./test/tools/test_disk_control ./$(TARGET) --disc "$$disc" --case 1 --quiet || rc=1; \
 		./test/tools/test_disk_control ./$(TARGET) --disc "$$disc" --case 3 --quiet || rc=1; \
+		./test/tools/test_disk_control ./$(TARGET) --disc "$$disc" --case 7 --quiet || rc=1; \
+		./test/tools/test_disk_control ./$(TARGET) --disc "$$disc" --case 8 --option virtualjaguar_memory_track=disabled --quiet || rc=1; \
 		discb=$$(find -L test/roms/private -iname '*.cdi' -o -iname '*.cue' 2>/dev/null | sed -n 2p); \
 		if [ -n "$$discb" ]; then \
 			if ./test/tools/test_disk_control ./$(TARGET) --disc "$$disc" --disc-b "$$discb" --case 4 --quiet; then :; \

README.md

@@ -27,7 +27,7 @@ None required. The Jaguar boot ROMs and CD BIOSes are embedded, and cartridges b
 | Cartridge | `j64`, `jag`, `rom`, `abs`, `cof`, `bin`, `prg` | Headerless raw homebrew is detected conservatively. Soft patching is covered in [`docs/rom-patches.md`](docs/rom-patches.md). |
 | Jaguar CD | `cue` (with `bin`), `cdi`, `chd` | `.iso` is not supported. CHD needs session metadata from a recent `chdman`; see [`docs/jagcd-chd.md`](docs/jagcd-chd.md). Each release attaches a suitable `chdman` as `jagcd-tools-*.zip`. |
 
-The core can also start with no content and take a disc through RetroArch's disk control. Cartridge EEPROM/SRAM and the CD Memory Track are saved as `<game>.srm` in RetroArch's `saves` folder; save states go in `states`. Exception: in a no-content session, a disc inserted through disk control gets no `.srm` (its Memory Track writes are not exposed to the frontend; use save states, or load the disc as content; [#810](https://github.com/libretro/virtualjaguar-libretro/issues/810)).
+The core can also start with no content and take a disc through RetroArch's disk control. Cartridge EEPROM/SRAM and the CD Memory Track are saved as `<game>.srm` in RetroArch's `saves` folder; save states go in `states`. Exception: a no-content session exposes the Memory Track as save RAM from the start ([#810](https://github.com/libretro/virtualjaguar-libretro/issues/810)), but with no content the frontend has nothing to name the `.srm` after, so it is not per-game and is not named after the disc you insert. Load the disc as content for per-game saves.
 
 ## Features
 

exports-test.list

@@ -71,6 +71,7 @@ _joypad1Buttons
 _InputDev*
 _Quad*
 _MTState*
+_mtMem
 _NVMBios*
 _NVM_*
 _JGD*

libretro.c

@@ -5560,6 +5560,16 @@ static bool disk_set_eject_state(bool ejected)
       return false;                   /* disk_ejected stays true */
    }
 
+   /* The boot just reset RAM, which wipes the Memory Track NVM BIOS module
+    * (the '_NVM' cookie + dispatcher stub) that no-content load installed.
+    * retro_load_game and retro_reset reinstall it after their boot for the
+    * same reason; without this, a game started by an insert sees the Memory
+    * Track cart but no NVM BIOS behind it, so the saves #810 exposes would
+    * never be written (#810). */
+   NVMBiosReset();
+   if (jaguarMemTrackInserted)
+      NVMBiosInstall();
+
    LOG_INF("[CD] disk control: inserted '%s', booting via '%s'\n",
            cd_image_path,
            bootConfig.strategy->name ? bootConfig.strategy->name : "?");
@@ -6652,14 +6662,38 @@ static void eeprom_unpack_save_buf(void)
       memcpy(mtMem, eeprom_save_buf + MT_SAVE_OFFSET, MT_SAVE_SIZE);
 }
 
+/* Does this session have anything for the frontend to persist?
+ *
+ * Only a no-content boot can answer no.  There, "no cartridge" used to mean
+ * "no save media" (#646: don't hand frontends a meaningless .srm for a bare
+ * BIOS), but #726 changed what a no-content boot IS: it comes up in the CD
+ * BIOS with the CD unit attached and the Memory Track cart plugged in from
+ * frame 0.  The Memory Track is real, writable save media whether or not a
+ * disc is mounted, so the answer follows it (#810).
+ *
+ * Deliberately NOT keyed on a disc being mounted.  libretro has no "save RAM
+ * changed" notification: frontends size the buffer and copy the .srm into it
+ * once, right after retro_load_game (RetroArch also sizes its autosave once,
+ * at init), and only re-query at shutdown.  Exposing the buffer for the first
+ * time after an insert would therefore be a write without a load -- the
+ * session's saves hit disk but are never read back, and each session blindly
+ * overwrites the last one's file.  So the answer has to be right at the FIRST
+ * query, which is why it keys on the Memory Track and nothing that can change
+ * later.  With the Memory Track disabled a no-content session keeps
+ * reporting nothing, and an inserted disc does not change that. */
+static bool save_ram_available(void)
+{
+   return !no_game_active || jaguarMemTrackInserted;
+}
+
 void *retro_get_memory_data(unsigned type)
 {
    if (type == RETRO_MEMORY_SYSTEM_RAM)
       return jaguarMainRAM;
    if (type == RETRO_MEMORY_SAVE_RAM)
    {
-      /* No-content boot (#646): no cartridge means no EEPROM chip. */
-      if (no_game_active)
+      /* No-content boot with no Memory Track and no disc (#646, #810). */
+      if (!save_ram_available())
          return NULL;
       /* Memory Track cart uses 128K NVRAM directly */
       if (jaguarMainROMCRC32 == 0xFDF37F47)
@@ -6680,10 +6714,9 @@ size_t retro_get_memory_size(unsigned type)
       return 0x200000;
    if (type == RETRO_MEMORY_SAVE_RAM)
    {
-      /* No-content boot (#646): no cartridge means no EEPROM chip -- report
-       * zero so frontends don't create a meaningless .srm for a bare BIOS
-       * session. */
-      if (no_game_active)
+      /* No-content boot with no Memory Track and no disc (#646, #810):
+       * nothing to persist, so don't create a meaningless .srm. */
+      if (!save_ram_available())
          return 0;
       if (jaguarMainROMCRC32 == 0xFDF37F47)
          return MT_SAVE_SIZE;

link-test.T

@@ -74,6 +74,7 @@
       InputDev*;
       Quad*;
       MTState*;
+      mtMem;
       NVMBios*;
       NVM_*;
       JGD*;

test/test_boot_config.c

@@ -614,7 +614,7 @@ TEST(no_game_boot_selects_cd_bios_strategy)
     core_teardown();
 }
 
-TEST(no_game_save_ram_is_empty)
+TEST(no_game_save_ram_is_memory_track)
 {
     bool loaded;
 
@@ -622,10 +622,16 @@ TEST(no_game_save_ram_is_empty)
     loaded = p_retro_load_game(NULL);
     if (!loaded) FAIL("retro_load_game(NULL) failed");
 
-    /* No cartridge -> no EEPROM chip.  A frontend must not be handed a
-     * meaningless .srm for a bare-BIOS session. */
-    ASSERT_EQ(p_retro_get_memory_size(RETRO_MEMORY_SAVE_RAM), 0);
-    ASSERT(p_retro_get_memory_data(RETRO_MEMORY_SAVE_RAM) == NULL);
+    /* Originally (#646) this asserted size 0: no cartridge, no EEPROM chip,
+     * so no .srm for a bare-BIOS session.  #726 made no-content boot a CD
+     * session with the Memory Track plugged in from frame 0, and #810 found
+     * that exposing nothing loses every save made through a disc inserted
+     * later: a frontend sizes and loads SAVE_RAM once, right after the load,
+     * so it has to be exposed from the FIRST query.  Memory Track is on by
+     * default; the disabled case is covered by test_disk_control case 8. */
+    ASSERT_EQ(p_retro_get_memory_size(RETRO_MEMORY_SAVE_RAM),
+              128 + 128 + 0x20000);
+    ASSERT(p_retro_get_memory_data(RETRO_MEMORY_SAVE_RAM) != NULL);
     core_teardown();
 }
 
@@ -724,7 +730,7 @@ int main(int argc, char *argv[])
     SUITE("No-Content Boot (RETRO_ENVIRONMENT_SET_SUPPORT_NO_GAME)");
     RUN(no_game_env_declared);
     RUN(no_game_boot_selects_cd_bios_strategy);
-    RUN(no_game_save_ram_is_empty);
+    RUN(no_game_save_ram_is_memory_track);
     RUN(no_game_runs_and_resets_without_crashing);
     total_fail += REPORT();
 

test/tools/test_disk_control.c

@@ -38,9 +38,30 @@
  *      only the return value would pass against the inert stub this
  *      interface shipped with one commit earlier.
  *
+ *   6  No-content boot exposes the Memory Track as SAVE_RAM from the very
+ *      first query (#810).  Needs no disc.  The size and pointer must be
+ *      CD_SAVE_SIZE and non-NULL straight after the load, and a marker the
+ *      "frontend" writes into the buffer before frame 1 must reach mtMem --
+ *      i.e. the .srm load a frontend does once, after retro_load_game,
+ *      actually lands.  A late-exposure fix would pass a size>0 check after
+ *      an insert and still lose every save, because that load already
+ *      happened against a size of 0.
+ *
+ *   7  Same, then insert a disc.  Size and pointer must be unchanged, the
+ *      marker must still be in mtMem (the insert's reboot must not wipe the
+ *      Memory Track), and the NVM BIOS module cookie must be present in RAM.
+ *
+ *   8  Memory Track DISABLED (--option virtualjaguar_memory_track=disabled):
+ *      nothing to persist on a bare no-content session, so SAVE_RAM is 0 --
+ *      and it STAYS 0 after a disc is inserted.  Deliberate: a frontend sizes
+ *      and loads the buffer once at load, so exposing it for the first time
+ *      after an insert would be a write without a load (the file is
+ *      overwritten at exit from a buffer that never saw it).  Guards against
+ *      "fixing" #810 by keying SAVE_RAM on a mounted disc.
+ *
  * Run: test_disk_control <core> --disc <image> --case N [--quiet]
- *      (--disc is required for cases 1, 3 and 4 only; case 5 is the
- *       no-content boot check and takes no disc.  Case 4 also needs --disc-b.)
+ *      (--disc is required for cases 1, 3, 4, 7 and 8; cases 5 and 6 are
+ *       no-disc no-content boot checks.  Case 4 also needs --disc-b.)
  */
 
 #define _DEFAULT_SOURCE 1
@@ -154,6 +175,48 @@ static void vid_cb(void *ud, const void *data, unsigned w, unsigned h,
     vid_prev_hash = hsh;
 }
 
+/* Mirrors libretro.c: 128 B cart EEPROM + 128 B CD EEPROM + 128 KB Memory
+ * Track.  Hard-coded on purpose -- a test that derived the expectation from
+ * the core's own constant could not catch that constant being wrong. */
+#define DC_CD_SAVE_SIZE   (128u + 128u + 0x20000u)
+#define DC_MT_SAVE_OFFSET 256u
+#define DC_MARKER_OFF     0x40u    /* offset inside the Memory Track        */
+#define DC_NVM_COOKIE_RAM 0x2400u  /* src/core/nvmbios.h NVM_COOKIE_ADDR    */
+
+static size_t (*lr_mem_size)(unsigned);
+static void  *(*lr_mem_data)(unsigned);
+static const uint8_t *mt_mem;      /* the core's real Memory Track array    */
+
+static const uint8_t dc_marker[8] = { 0xA5, 0x5A, 0xC3, 0x3C,
+                                      0x81, 0x18, 0xE7, 0x7E };
+
+/* Stand in for the frontend loading a .srm: it asks for the size and the
+ * pointer once, after retro_load_game, and copies the file into the buffer. */
+static int seed_srm_marker(void)
+{
+    uint8_t *buf = (uint8_t *)lr_mem_data(RETRO_MEMORY_SAVE_RAM);
+
+    if (!buf || lr_mem_size(RETRO_MEMORY_SAVE_RAM) != DC_CD_SAVE_SIZE)
+        return 0;
+    memcpy(buf + DC_MT_SAVE_OFFSET + DC_MARKER_OFF, dc_marker,
+           sizeof(dc_marker));
+    return 1;
+}
+
+/* jaguarMainRAM is a POINTER variable into jagMemSpace, so dlsym returns
+ * the address of the pointer, not of the RAM (cf. cd_wedge_probe.c). */
+static const uint8_t *main_ram(harness_config *c)
+{
+    uint8_t **ramp = (uint8_t **)harness_dlsym(c, "jaguarMainRAM");
+
+    return ramp ? *ramp : NULL;
+}
+
+static int marker_in_mtmem(void)
+{
+    return memcmp(mt_mem + DC_MARKER_OFF, dc_marker, sizeof(dc_marker)) == 0;
+}
+
 static harness_result mkres(int ok, const char *name, const char *detail)
 {
     harness_result r;
@@ -167,7 +230,7 @@ int main(int argc, char **argv)
 {
     harness_config cfg = HARNESS_CONFIG_DEFAULT;
     struct retro_game_info gi;
-    harness_result results[6];
+    harness_result results[8];
     unsigned nres = 0;
     const char *disc_path = NULL;
     const char *disc_path_b = NULL;
@@ -185,18 +248,20 @@ int main(int argc, char **argv)
             disc_path_b = argv[i + 1];
     }
     if (case_num != 1 && case_num != 3 && case_num != 4
-        && case_num != 5) {
+        && case_num != 5 && case_num != 6 && case_num != 7
+        && case_num != 8) {
         fprintf(stderr, "usage: test_disk_control <core> --case N "
                         "[--disc <image>] [--disc-b <image>] [--quiet]\n"
-                        "  N is one of 1|3|4|5.  Cases 1, 3 and 4 need "
-                        "--disc <image>; case 4 also needs\n"
-                        "  --disc-b <image>.  Case 5 (no-content boot) "
-                        "takes no disc.\n"
+                        "  N is one of 1|3|4|5|6|7|8.  Cases 1, 3, 4, 7 and 8 "
+                        "need --disc <image>; case 4 also needs\n"
+                        "  --disc-b <image>.  Cases 5 and 6 (no-content "
+                        "boot) take no disc.  Case 8 also wants\n"
+                        "  --option virtualjaguar_memory_track=disabled.\n"
                         "  (case 2 needs a one-session audio disc; none "
                         "exists in the corpus)\n");
         return 1;
     }
-    if (!disc_path && case_num != 5) {
+    if (!disc_path && case_num != 5 && case_num != 6) {
         fprintf(stderr, "test_disk_control: no --disc given\n");
         return 1;
     }
@@ -226,6 +291,17 @@ int main(int argc, char **argv)
         return 1;
     }
 
+    lr_mem_size = (size_t (*)(unsigned))harness_dlsym(&cfg,
+                                            "retro_get_memory_size");
+    lr_mem_data = (void *(*)(unsigned))harness_dlsym(&cfg,
+                                            "retro_get_memory_data");
+    mt_mem      = (const uint8_t *)harness_dlsym(&cfg, "mtMem");
+    if (!lr_mem_size || !lr_mem_data || !mt_mem) {
+        fprintf(stderr, "test_disk_control: memory accessors / mtMem not "
+                        "exported -- rebuild with `make TEST_EXPORTS=1`\n");
+        return 1;
+    }
+
     if (!harness_load_no_content(&cfg)) {
         fprintf(stderr, "test_disk_control: no-content load failed\n");
         return 1;
@@ -373,6 +449,129 @@ int main(int argc, char **argv)
         pass = rendered && moving;
         break;
     }
+    case 6: {
+        /* #810: the buffer must be exposed from the FIRST query, because a
+         * frontend sizes and loads it exactly once, right after the load.
+         * (Memory Track enabled is the default; it is plugged in from frame
+         * 0 on this path, see the no-content branch of retro_load_game.) */
+        int sized, seeded, landed, stable;
+        size_t size_at_load = lr_mem_size(RETRO_MEMORY_SAVE_RAM);
+        void  *ptr_at_load  = lr_mem_data(RETRO_MEMORY_SAVE_RAM);
+
+        sized  = size_at_load == DC_CD_SAVE_SIZE && ptr_at_load != NULL;
+        seeded = sized && seed_srm_marker();
+        harness_step(&cfg);                 /* first frame unpacks the .srm */
+        landed = seeded && marker_in_mtmem();
+        harness_step(&cfg);
+        stable = lr_mem_data(RETRO_MEMORY_SAVE_RAM) == ptr_at_load
+              && lr_mem_size(RETRO_MEMORY_SAVE_RAM) == DC_CD_SAVE_SIZE;
+
+        results[nres++] = mkres(sized, "case6_save_ram_exposed_at_load",
+            sized ? "no-content boot reports CD_SAVE_SIZE and a buffer at "
+                    "load time"
+                  : "SAVE_RAM is size 0 / NULL on a no-content boot with "
+                    "the Memory Track plugged in (#810)");
+        results[nres++] = mkres(landed, "case6_srm_load_reaches_mtmem",
+            landed ? "data the frontend wrote into SAVE_RAM reached the "
+                     "Memory Track"
+                   : "frontend-loaded save data never reached mtMem");
+        results[nres++] = mkres(stable, "case6_buffer_stable",
+            stable ? "pointer and size unchanged across frames"
+                   : "pointer or size moved under the frontend");
+        pass = sized && seeded && landed && stable;
+        break;
+    }
+    case 7: {
+        int sized, seeded, inserted, same, kept, nvm, nvm0, i;
+        const uint8_t *ram;
+        void *ptr_before = lr_mem_data(RETRO_MEMORY_SAVE_RAM);
+
+        sized  = lr_mem_size(RETRO_MEMORY_SAVE_RAM) == DC_CD_SAVE_SIZE
+              && ptr_before != NULL;
+        seeded = sized && seed_srm_marker();
+        /* Control for the cookie probe below: it must be present straight
+         * after the no-content load, or "missing after the insert" would
+         * only mean the probe is looking at the wrong address. */
+        ram    = main_ram(&cfg);
+        nvm0   = ram && memcmp(ram + DC_NVM_COOKIE_RAM, "_NVM", 4) == 0;
+        harness_step(&cfg);                 /* first frame unpacks the .srm */
+
+        gi.path  = disc_path;
+        inserted = cfg.disk_cb_registered
+                && cfg.disk_add_image_index()
+                && cfg.disk_replace_image_index(0, &gi)
+                && cfg.disk_set_eject_state(true)
+                && cfg.disk_set_eject_state(false);
+        /* Sampled BEFORE any frame runs: the boot has just reset the machine,
+         * so nothing the game does can have touched $2400 yet, and a missing
+         * cookie here is the insert path's doing, not the game's. */
+        ram  = main_ram(&cfg);
+        nvm  = ram && memcmp(ram + DC_NVM_COOKIE_RAM, "_NVM", 4) == 0;
+        for (i = 0; i < 30; i++)
+            harness_step(&cfg);
+
+        same = lr_mem_size(RETRO_MEMORY_SAVE_RAM) == DC_CD_SAVE_SIZE
+            && lr_mem_data(RETRO_MEMORY_SAVE_RAM) == ptr_before;
+        kept = seeded && marker_in_mtmem();
+
+        results[nres++] = mkres(seeded, "case7_exposed_before_insert",
+            seeded ? "SAVE_RAM exposed and seeded before the insert"
+                   : "SAVE_RAM not exposed before the insert");
+        results[nres++] = mkres(inserted, "case7_insert_succeeded",
+            inserted ? "disc inserted" : "insert was refused");
+        results[nres++] = mkres(same, "case7_save_ram_after_insert",
+            same ? "size and pointer unchanged by the insert"
+                 : "SAVE_RAM size/pointer changed or vanished after the "
+                   "insert (#810)");
+        results[nres++] = mkres(kept, "case7_memory_track_survives_insert",
+            kept ? "Memory Track contents survived the insert reboot"
+                 : "the insert reboot wiped the Memory Track -- the next "
+                   "frontend save would write it back blank");
+        results[nres++] = mkres(nvm0, "case7_nvm_module_at_load",
+            nvm0 ? "'_NVM' cookie present after the no-content load"
+                 : "'_NVM' cookie missing straight after the no-content "
+                   "load -- the probe address is wrong");
+        results[nres++] = mkres(nvm, "case7_nvm_module_present",
+            nvm ? "'_NVM' cookie present after the insert reboot"
+                : "'_NVM' cookie missing after the insert reboot -- games "
+                  "launched by insert would not see the Memory Track");
+        pass = seeded && nvm0 && inserted && same && kept && nvm;
+        break;
+    }
+    case 8: {
+        /* Memory Track disabled: a bare no-content session has nothing to
+         * persist and keeps reporting 0 (the pre-#810 contract).  Mounting a
+         * disc must NOT flip that mid-session -- see the header comment. */
+        int bare_zero, inserted, still_zero;
+
+        bare_zero = lr_mem_size(RETRO_MEMORY_SAVE_RAM) == 0
+                 && lr_mem_data(RETRO_MEMORY_SAVE_RAM) == NULL;
+
+        gi.path  = disc_path;
+        inserted = cfg.disk_cb_registered
+                && cfg.disk_add_image_index()
+                && cfg.disk_replace_image_index(0, &gi)
+                && cfg.disk_set_eject_state(true)
+                && cfg.disk_set_eject_state(false);
+        harness_step(&cfg);
+        still_zero = lr_mem_size(RETRO_MEMORY_SAVE_RAM) == 0
+                  && lr_mem_data(RETRO_MEMORY_SAVE_RAM) == NULL;
+
+        results[nres++] = mkres(bare_zero, "case8_bare_session_has_no_save_ram",
+            bare_zero ? "no Memory Track, no disc: SAVE_RAM is 0/NULL"
+                      : "bare session exposes SAVE_RAM with nothing to save "
+                        "(is the memory_track option actually disabled?)");
+        results[nres++] = mkres(inserted, "case8_insert_succeeded",
+            inserted ? "disc inserted" : "insert was refused");
+        results[nres++] = mkres(still_zero, "case8_save_ram_stays_unexposed",
+            still_zero ? "SAVE_RAM still 0/NULL after the insert (no write "
+                         "without a load)"
+                       : "SAVE_RAM appeared mid-session: the frontend never "
+                         "loaded the .srm into it, so its exit save would "
+                         "clobber the previous session's file");
+        pass = bare_zero && inserted && still_zero;
+        break;
+    }
     case 3: {
         int added, refused, still_ejected, unchanged, still_runs;