From f54a8fc3f0017bb1f0be25464e105b314c8becc0 Mon Sep 17 00:00:00 2001
From: Ryan Dwyer <ryandwyer1@gmail.com>
Date: Thu, 7 Oct 2021 21:23:59 +1000
Subject: [PATCH] Disassemble getReturnAddress

---
 ld/libfiles.ntsc-beta.inc |  1 +
 src/lib/getra.s           | 45 +++++++++++++++++++++++++++++++++++++++
 src/lib/lib_0c000.c       | 28 ------------------------
 src/lib/lib_18680.s       |  1 +
 4 files changed, 47 insertions(+), 28 deletions(-)
 create mode 100644 src/lib/getra.s

diff --git a/ld/libfiles.ntsc-beta.inc b/ld/libfiles.ntsc-beta.inc
index df08ce17d..54356f2d2 100644
--- a/ld/libfiles.ntsc-beta.inc
+++ b/ld/libfiles.ntsc-beta.inc
@@ -34,6 +34,7 @@
 	build/ROMID/lib/lib_09a80.o (section); \
 	build/ROMID/lib/lib_0bfb0.o (section); \
 	build/ROMID/lib/lib_0c000.o (section); \
+	build/ROMID/lib/getra.o (section); \
 	build/ROMID/lib/dma.o (section); \
 	build/ROMID/lib/main.o (section); \
 	build/ROMID/lib/snd.o (section); \
diff --git a/src/lib/getra.s b/src/lib/getra.s
new file mode 100644
index 000000000..a8d1c2b2b
--- /dev/null
+++ b/src/lib/getra.s
@@ -0,0 +1,45 @@
+#include "macros.h"
+.set noat
+.set noreorder
+
+/**
+ * Get the return address ($ra) that the caller would return to.
+ *
+ * For example, a C function could use:
+ *
+ *     osSyncPrintf("Called from %u\n", getReturnAddress());
+ *
+ * It follows the current $ra to get to the function that called
+ * getReturnAddress, then steps backwards through that function's bytecode until
+ * it finds either `addiu $sp` or `sw $ra, 0xnn($sp)`.
+ *
+ * If it finds `addiu $sp` first then it's reached the top of the function and
+ * $ra wasn't saved to the stack. In this case something is massively wrong and
+ * the function returns -1.
+ *
+ * If it finds `sw $ra, 0xnn($sp)` first then it reads the stack offset out of
+ * the instruction, then reads the value out of the stack using that offset.
+ */
+glabel getReturnAddress
+	or     $a0, $ra, $zero
+	addiu  $v0, $zero, -1
+.loop:
+	lw     $t0, 0($a0)
+	addiu  $t2, $zero, 0x27bd
+	srl    $t1, $t0, 16
+	beq    $t1, $t2, .foundtop
+	nop
+	dli    $t2, 0xafbf
+	beql   $t1, $t2, .foundstore
+	sll    $t2, $t0, 16
+	j      .loop
+	addiu  $a0, $a0, -4
+
+	sll    $t2, $t0, 16
+.foundstore:
+	sra    $t2, $t2, 16
+	add    $t2, $t2, $sp
+	lw     $v0, 0($t2)
+.foundtop:
+	jr     $ra
+	nop
diff --git a/src/lib/lib_0c000.c b/src/lib/lib_0c000.c
index 955280ddb..4cd14a645 100644
--- a/src/lib/lib_0c000.c
+++ b/src/lib/lib_0c000.c
@@ -1546,31 +1546,3 @@ void func0000cf54(u16 *fb)
 		}
 	}
 }
-
-#if VERSION < VERSION_NTSC_1_0
-GLOBAL_ASM(
-glabel func0000d678nb
-/*     d678:	00000000 */ 	sll	$zero,$zero,0x0
-/*     d67c:	00000000 */ 	sll	$zero,$zero,0x0
-/*     d680:	03e02025 */ 	or	$a0,$ra,$zero
-/*     d684:	2402ffff */ 	addiu	$v0,$zero,-1
-/*     d688:	8c880000 */ 	lw	$t0,0x0($a0)
-/*     d68c:	240a27bd */ 	addiu	$t2,$zero,0x27bd
-/*     d690:	00084c02 */ 	srl	$t1,$t0,0x10
-/*     d694:	112a000a */ 	beq	$t1,$t2,.NB0000d6c0
-/*     d698:	00000000 */ 	sll	$zero,$zero,0x0
-/*     d69c:	340aafbf */ 	dli	$t2,0xafbf
-/*     d6a0:	512a0004 */ 	beql	$t1,$t2,.NB0000d6b4
-/*     d6a4:	00085400 */ 	sll	$t2,$t0,0x10
-/*     d6a8:	080035a2 */ 	j	0xd688
-/*     d6ac:	2484fffc */ 	addiu	$a0,$a0,-4
-/*     d6b0:	00085400 */ 	sll	$t2,$t0,0x10
-.NB0000d6b4:
-/*     d6b4:	000a5403 */ 	sra	$t2,$t2,0x10
-/*     d6b8:	015d5020 */ 	add	$t2,$t2,$sp
-/*     d6bc:	8d420000 */ 	lw	$v0,0x0($t2)
-.NB0000d6c0:
-/*     d6c0:	03e00008 */ 	jr	$ra
-/*     d6c4:	00000000 */ 	sll	$zero,$zero,0x0
-);
-#endif
diff --git a/src/lib/lib_18680.s b/src/lib/lib_18680.s
index 291230189..1e1b9be00 100644
--- a/src/lib/lib_18680.s
+++ b/src/lib/lib_18680.s
@@ -1,3 +1,4 @@
+#include "versions.h"
 #include "macros.inc"
 .set noat
 .set noreorder