runtime: load sp and pc inside tinygo_longjmp

This is a small change to make it easier to support architectures that
need to restore more than just the sp and pc registers. In particular,
it is needed for the AVR architecture that needs to restore the frame
pointer (Y register).

Author: aykevl

src/runtime/asm_386.S

@@ -28,6 +28,7 @@ tinygo_scanCurrentStack:
 tinygo_longjmp:
     // Note: the code we jump to assumes eax is set to a non-zero value if we
     // jump from here.
-    movl 8(%esp), %eax // jumpPC (stash in volatile register)
-    movl 4(%esp), %esp // jumpSP
+    movl 4(%esp), %eax
+    movl 0(%eax), %esp // jumpSP
+    movl 4(%eax), %eax // jumpPC (stash in volatile register)
     jmpl *%eax

src/runtime/asm_amd64.S

@@ -37,11 +37,11 @@ tinygo_longjmp:
 .global _tinygo_longjmp
 _tinygo_longjmp:
 #endif
-    // Note: the code we jump to assumes rax is non-zero so we have to load it
-    // with some value here.
-    movq $1, %rax
-    movq %rdi, %rsp // jumpSP
-    jmpq *%rsi      // jumpPC
+    // Note: the code we jump to assumes rax is set to a non-zero value if we
+    // jump from here, so we use rax as the temporary value for jumpPC.
+    movq 0(%rdi), %rsp // jumpSP
+    movq 8(%rdi), %rax // jumpPC
+    jmpq *%rax
 
 
 #ifdef __MACH__ // Darwin

src/runtime/asm_amd64_windows.S

@@ -24,8 +24,8 @@ tinygo_scanCurrentStack:
 .section .text.tinygo_longjmp,"ax"
 .global tinygo_longjmp
 tinygo_longjmp:
-    // Note: the code we jump to assumes rax is non-zero so we have to load it
-    // with some value here.
-    movq $1, %rax
-    movq %rcx, %rsp // jumpSP
-    jmpq *%rdx      // jumpPC
+    // Note: the code we jump to assumes rax is set to a non-zero value if we
+    // jump from here, so we use rax as the temporary value for jumpPC.
+    movq 0(%rcx), %rsp // jumpSP
+    movq 8(%rcx), %rax // jumpPC
+    jmpq *%rax

src/runtime/asm_arm.S

@@ -40,6 +40,8 @@ tinygo_longjmp:
     .cfi_startproc
     // Note: the code we jump to assumes r0 is set to a non-zero value if we
     // jump from here (which is conveniently already the case).
+
+    ldm r0, {r0, r1}
     mov sp, r0 // jumpSP
     mov pc, r1 // jumpPC
     .cfi_endproc

src/runtime/asm_arm64.S

@@ -43,5 +43,6 @@ tinygo_longjmp:
 #endif
     // Note: the code we jump to assumes x0 is set to a non-zero value if we
     // jump from here (which is conveniently already the case).
-    mov sp, x0 // jumpSP
-    br  x1     // jumpPC
+    ldp x1, x2, [x0] // jumpSP, jumpPC
+    mov sp, x1
+    br  x2

src/runtime/asm_riscv.S

@@ -46,6 +46,7 @@ tinygo_scanCurrentStack:
 .global tinygo_longjmp
 tinygo_longjmp:
     // Note: the code we jump to assumes a0 is non-zero, which is already the
-    // case because that's jumpSP (the stack pointer).
-    mv sp, a0 // jumpSP
-    jr a1     // jumpPC
+    // case because that's the defer frame pointer.
+    lw sp, 0(a0)       // jumpSP
+    lw a1, REGSIZE(a0) // jumpPC
+    jr a1

src/runtime/panic.go

@@ -13,7 +13,7 @@ func trap()
 // Inline assembly stub. It is essentially C longjmp but modified a bit for the
 // purposes of TinyGo. It restores the stack pointer and jumps to the given pc.
 //export tinygo_longjmp
-func tinygo_longjmp(sp, pc unsafe.Pointer)
+func tinygo_longjmp(frame *task.DeferFrame)
 
 // Compiler intrinsic.
 // Returns whether recover is supported on the current architecture.
@@ -26,7 +26,7 @@ func _panic(message interface{}) {
 		if frame != nil {
 			frame.PanicValue = message
 			frame.Panicking = true
-			tinygo_longjmp(frame.JumpSP, frame.JumpPC)
+			tinygo_longjmp(frame)
 			// unreachable
 		}
 	}