From 905b4edfa88d79092835bb4235e53e778a5b24f8 Mon Sep 17 00:00:00 2001
From: TH3BACKLOG <th3backlog89@gmail.com>
Date: Mon, 13 Jul 2026 08:50:36 -0400
Subject: [PATCH] fix(recomp): advance ctx->pc on fallthrough functions with no
 terminating branch (#168)

* fix(recomp): advance ctx->pc on fallthrough functions with no terminating branch

FunctionEmitter::emit only ever advances ctx->pc via the per-instruction
`ctx->pc = 0x<addr>u;` assignment (overwritten by the next instruction in
the same function) or via handleBranchDelaySlots when the last instruction
is a branch/jump. A function whose last instruction is neither (e.g. a
lone padduw/NOP-style instruction with no terminator) leaves ctx->pc
pointing at its own last instruction forever after returning, since
nothing ever advances it to the next function.

dispatchLoop then reads ctx->pc, looks up the same function, and calls it
again -- forever. No exception, no crash, just an infinite loop that
silently never makes forward progress.

Reproduced on SDBZ's SLUS_214.42 ELF entry point: 0x100008 is emitted as a
standalone 1-instruction function (padduw $at, $zero, $zero) with no
branch, causing dispatchLoop to spin on pc=0x100008 indefinitely.

Fix: track whether the last processed instruction had a delay slot (i.e.
was a branch/jump); if the function ends without one, emit an
unconditional ctx->pc = function.end before closing the function so
dispatchLoop resumes at the next function instead of spinning.

* review: trim overly verbose comment per ran-j feedback
---
 ps2xRecomp/src/lib/function_emitter.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/ps2xRecomp/src/lib/function_emitter.cpp b/ps2xRecomp/src/lib/function_emitter.cpp
index af98cda..53a6005 100644
--- a/ps2xRecomp/src/lib/function_emitter.cpp
+++ b/ps2xRecomp/src/lib/function_emitter.cpp
@@ -103,9 +103,12 @@ namespace ps2recomp
            << std::dec;
         ss << "\n";
 
+        bool lastInstructionWasControlFlow = false;
+
         for (size_t i = 0; i < instructions.size(); ++i)
         {
             const Instruction &inst = instructions[i];
+            lastInstructionWasControlFlow = inst.hasDelaySlot;
 
             if (internalTargets.contains(inst.address))
             {
@@ -223,6 +226,13 @@ namespace ps2recomp
             }
         }
 
+        // Fallthrough with no terminating branch: advance ctx->pc past the function so dispatchLoop doesn't re-call it forever.
+        if (!instructions.empty() && !lastInstructionWasControlFlow)
+        {
+            ss << "    ctx->pc = 0x" << std::hex << function.end << "u;\n"
+               << std::dec;
+        }
+
         ss << "}\n";
         return ss.str();
     }