From: Daniel Golle <daniel@makrotopia.org>
Subject: [PATCH] JavaScriptCore: BBQJIT: implement wasm tail call on RISCV64

emitTailCall (direct) and emitIndirectTailCall in WasmBBQJIT.cpp branch
on the host CPU to set up the caller's frame pointer + return address
for the tail-jumped callee. ARM64/ARMv7 use loadPairPtr(fp, callerFP, lr)
to read both at once; X86_64 has its own dedicated branch; everything
else trips UNREACHABLE_FOR_PLATFORM() -> SIGABRT during BBQ compilation
of any wasm function that uses return_call (tail call).

RISC-V's standard prologue saves fp and ra adjacent at [sp, sp+8]
(same layout as ARM64), so the ARM64 loadPair64-backed loadPairPtr
also works on RISCV64. The "fix SP and FP" sequence (addPtr to
stackPointerRegister + move callerFramePointer -> framePointerRegister)
is also generic. Add CPU(RISCV64) to all three guarded branches.

Reproducer: spec-tests/try_table.wast.js line 117
(assert_exception(() => call($2, "return-call-in-try-catch", []))).
BBQ aborts during compilation of the wasm function that does
return_call inside try-catch.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
--- a/Source/JavaScriptCore/wasm/WasmBBQJIT.cpp
+++ b/Source/JavaScriptCore/wasm/WasmBBQJIT.cpp
@@ -4381,7 +4381,7 @@ void BBQJIT::emitTailCall(FunctionSpaceI
     m_jit.loadPtr(Address(MacroAssembler::framePointerRegister), callerFramePointer);
     resolvedArguments.append(Value::pinned(pointerType(), Location::fromStack(sizeof(Register))));
     parameterLocations.append(Location::fromStack(tailCallStackOffsetFromFP + Checked<int>(sizeof(Register))));
-#elif CPU(ARM64) || CPU(ARM_THUMB2)
+#elif CPU(ARM64) || CPU(ARM_THUMB2) || CPU(RISCV64)
     m_jit.loadPairPtr(MacroAssembler::framePointerRegister, callerFramePointer, MacroAssembler::linkRegister);
 #else
     UNUSED_PARAM(callerFramePointer);
@@ -4652,7 +4652,7 @@ void BBQJIT::emitIndirectTailCall(const
 
     resolvedArguments.append(Value::pinned(pointerType(), Location::fromStack(sizeof(Register))));
     parameterLocations.append(Location::fromStack(tailCallStackOffsetFromFP + Checked<int>(sizeof(Register))));
-#elif CPU(ARM64) || CPU(ARM_THUMB2)
+#elif CPU(ARM64) || CPU(ARM_THUMB2) || CPU(RISCV64)
     auto preserved = callingConvention.argumentGPRs();
     preserved.add(importableFunction, IgnoreVectors);
     if constexpr (isARM64E())
@@ -4709,7 +4709,7 @@ void BBQJIT::emitIndirectTailCall(const
     m_jit.loadPtr(Address(MacroAssembler::framePointerRegister, tailCallStackOffsetFromFP), wasmScratchGPR);
     m_jit.addPtr(TrustedImm32(tailCallStackOffsetFromFP + Checked<int>(sizeof(Register))), MacroAssembler::framePointerRegister, MacroAssembler::stackPointerRegister);
     m_jit.move(wasmScratchGPR, MacroAssembler::framePointerRegister);
-#elif CPU(ARM64) || CPU(ARM_THUMB2)
+#elif CPU(ARM64) || CPU(ARM_THUMB2) || CPU(RISCV64)
     m_jit.addPtr(TrustedImm32(tailCallStackOffsetFromFP + Checked<int>(sizeof(CallerFrameAndPC))), MacroAssembler::framePointerRegister, MacroAssembler::stackPointerRegister);
     m_jit.move(callerFramePointer, MacroAssembler::framePointerRegister);
 #else