Emulator

Is the bug that Dolphin does not create a virtual disc in memory as it should, or just that it fails to boot it? If it's the latter, you should set the Default ISO path to the sys/main.dol file of a virtual disc (the actual content of this DOL file doesn't really matter), and then launch the DOL/ELF file you want to run from a location which is not part of the virtual disc.

That is similar to how it used to work (using "default iso"). The problem now seems to be that IsValidDirectoryBlob checks explicitly for "/sys/main.dol". Currently if Default ISO is set and a elf file is launched, IsValidDirectoryBlob is called with the path to the elf, and DirectoryBlob object is not created.

So after setting default iso to a path which ends in "/sys/main.dol", and executing an elf file, the problem is that the apploader is not executed and therefor the value at 0x80000038 remains 0, while it should point to the fst. The proper thing to do is to convert the elf to a dol in memory (accessible via the virtual disc), and run the apploader. I assume this (effectively) happened before.

Dolphin never ran apploaders for ELF files, but it seems like it did write to 0x80000038 manually. I dropped that part of the code, presumably because it seemed to be of no use for running games, but I suppose there would be no harm in readding it.

https://github.com/dolphin-emu/dolphin/blob/5.0/Source/Core/Core/Boot/Boot.cpp#L76

I think it was covered before by running apploader https://github.com/dolphin-emu/dolphin/blob/5.0/Source/Core/Core/Boot/Boot.cpp#L413 or initialized by dolphin, yes. Is it worth doing 'correctly' now, or just always initializing the fields in e.g. here https://github.com/dolphin-emu/dolphin/blob/master/Source/Core/Core/Boot/Boot.cpp#L544 ?

if i manually convert the elf to dol outside of dolphin, then add some code to run apploader, it at least works:

diff --git a/Source/Core/Core/Boot/Boot.cpp b/Source/Core/Core/Boot/Boot.cpp
index 0ad7f6ec12..cd27d8ff33 100644
--- a/Source/Core/Core/Boot/Boot.cpp
+++ b/Source/Core/Core/Boot/Boot.cpp
@@ -466,11 +466,12 @@ bool CBoot::Load_BS2(const std::string& boot_rom_filename)
   return true;
 }

-static void SetDefaultDisc()
+static std::optional<const DiscIO::VolumeDisc*> SetDefaultDisc()
 {
   const std::string default_iso = Config::Get(Config::MAIN_DEFAULT_ISO);
   if (!default_iso.empty())
-    SetDisc(DiscIO::CreateDisc(default_iso));
+    return SetDisc(DiscIO::CreateDisc(default_iso));
+  return {};
 }

 static void CopyDefaultExceptionHandlers()
@@ -529,14 +530,16 @@ bool CBoot::BootUp(std::unique_ptr<BootParameters> boot)
       if (!executable.reader->IsValid())
         return false;

-      if (!executable.reader->LoadIntoMemory())
+      auto default_disc = SetDefaultDisc();
+      if (!default_disc)
       {
-        PanicAlertFmtT("Failed to load the executable to memory.");
-        return false;
+        if (!executable.reader->LoadIntoMemory())
+        {
+          PanicAlertFmtT("Failed to load the executable to memory.");
+          return false;
+        }
       }

-      SetDefaultDisc();
-
       SetupMSR();
       SetupBAT(config.bWii);
       CopyDefaultExceptionHandlers();
@@ -560,6 +563,11 @@ bool CBoot::BootUp(std::unique_ptr<BootParameters> boot)
         SetupGCMemory();
       }

+      if (default_disc)
+      {
+        RunApploader(config.bWii, **default_disc, {});
+      }
+
       SConfig::OnNewTitleLoad();

       PC = executable.reader->GetEntryPoint();
diff --git a/Source/Core/Core/Boot/Boot_BS2Emu.cpp b/Source/Core/Core/Boot/Boot_BS2Emu.cpp
index 1265317a90..feec60b4cd 100644
--- a/Source/Core/Core/Boot/Boot_BS2Emu.cpp
+++ b/Source/Core/Core/Boot/Boot_BS2Emu.cpp
@@ -372,7 +372,7 @@ bool CBoot::SetupWiiMemory(IOS::HLE::IOSC::ConsoleType console_type)
   values in this region will also be placed here by the game as it boots.
   They are:
   0x80000038  Start of FST
-  0x8000003c  Size of FST Size
+  0x8000003c  Size of FST
   0x80000060  Copyright code
   */

diff --git a/Source/Core/DiscIO/DirectoryBlob.cpp b/Source/Core/DiscIO/DirectoryBlob.cpp
index 86de55595a..30005759b5 100644
--- a/Source/Core/DiscIO/DirectoryBlob.cpp
+++ b/Source/Core/DiscIO/DirectoryBlob.cpp
@@ -1087,7 +1087,7 @@ void DirectoryBlobPartition::BuildFST(std::vector<FSTBuilderNode> root_nodes, u6
   // overflow check, compare the aligned name offset with the aligned name table size
   ASSERT(Common::AlignUp(name_offset, 1ull << m_address_shift) == name_table_size);

-  // write FST size and location
+  // write FST location, size and max size
   Write32((u32)(fst_address >> m_address_shift), 0x0424, &m_disc_header);
   Write32((u32)(m_fst_data.size() >> m_address_shift), 0x0428, &m_disc_header);
   Write32((u32)(m_fst_data.size() >> m_address_shift), 0x042c, &m_disc_header);

is that an OK change? it would be nicer if the DirectoryBlob's main.dol gets overridden with whatever executable you've launched but...at least it works.

issue can be closed i guess: "default iso" with path set to /sys/main.dol has to be used, and there is no support for elf or different dol path.