Stack walk: Report a function's symbol start as its entry, not its prologue

The scan for the prologue took the addiu sp as the entry, which is past the
start when the function does something first (a lui, a move).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Core/MIPS/MIPSStackWalk.cpp

@@ -145,7 +145,10 @@ namespace MIPSStackWalk {
 					continue;
 				}
 
-				frame.entry = pc;
+				// The prologue often isn't the first instruction (a lui or move can come first), so
+				// the function's symbol, if it has one, gives the real entry.
+				const u32 symbolEntry = GuessEntry(pc);
+				frame.entry = symbolEntry != INVALIDTARGET ? symbolEntry : pc;
 				frame.stackSize = -_IMM16;
 				if (ra_offset != -1 && Memory::IsValid4AlignedAddress(frame.sp + ra_offset)) {
 					ra = Memory::ReadUnchecked_U32(frame.sp + ra_offset);

unittest/UnitTest.cpp

@@ -2501,6 +2501,29 @@ static bool CheckStackWalk() {
 	EXPECT_EQ_HEX(frames[1].pc, caller + 0x10);
 	EXPECT_EQ_HEX(frames[1].entry, caller);
 	EXPECT_EQ_INT(frames[1].stackSize, 16);
+
+	// With a symbol, the entry is where it starts, even when the prologue isn't first.
+	const u32 func = 0x08805000;
+	const u32 funcCode[] = {
+		0x3C080000,  // func: lui t0, 0
+		0x27BDFFF0,  // addiu sp, sp, -16
+		0xAFBF000C,  // sw ra, 12(sp)
+		0x00000000,  // nop
+	};
+	for (size_t i = 0; i < ARRAY_SIZE(funcCode); i++) {
+		Memory::WriteUnchecked_U32(funcCode[i], func + (u32)i * 4);
+	}
+	Memory::WriteUnchecked_U32(caller + 0x10, sp + 12);
+	symbolMap.AddFunction("func", func, sizeof(funcCode));
+	symbolMap.SortSymbols();
+	g_symbolMap = &symbolMap;
+	frames = MIPSStackWalk::Walk(func + 0xC, caller + 0x10, sp, caller, 0x09F00000);
+	g_symbolMap = nullptr;
+
+	EXPECT_EQ_INT((int)frames.size(), 2);
+	EXPECT_EQ_HEX(frames[0].entry, func);
+	EXPECT_EQ_INT(frames[0].stackSize, 16);
+	EXPECT_EQ_HEX(frames[1].pc, caller + 0x10);
 	return true;
 }