runtime: move/refactor some GC-related code

Instead of putting tinygo_scanCurrentStack in scheduler_*.S files, put
them in dedicated files. The function tinygo_scanCurrentStack has
nothing to do with scheduling and so doesn't belong there. Additionally,
while scheduling code is made specific for the Cortex-M, the
tinygo_scanCurrentStack is generic to all ARM targets so this move
removes some duplication there.

Specifically:

  * tinygo_scanCurrentStack is moved out of scheduler_cortexm.S as it
    isn't really part of the scheduler. It is now gc_arm.S.
  * Same for the AVR target.
  * Same for the RISCV target.
  * scheduler_gba.S is removed, using gc_arm.S instead as it only
    contains tinygo_scanCurrentStack.

src/runtime/gc_arm.S

@@ -1,14 +1,25 @@
+// Only generate .debug_frame, don't generate .eh_frame.
+.cfi_sections .debug_frame
+
 .section .text.tinygo_scanCurrentStack
 .global  tinygo_scanCurrentStack
 .type    tinygo_scanCurrentStack, %function
 tinygo_scanCurrentStack:
+    .cfi_startproc
     // Save callee-saved registers onto the stack.
+    #if defined(__thumb2__)
+    push {r4-r11, lr}
+    .cfi_def_cfa_offset 9*4
+    #else
     mov r0, r8
     mov r1, r9
     mov r2, r10
     mov r3, r11
     push {r0-r3, lr}
+    .cfi_def_cfa_offset 5*4
     push {r4-r7}
+    .cfi_def_cfa_offset 4*4
+    #endif
 
     // Scan the stack.
     mov r0, sp
@@ -16,4 +27,7 @@ tinygo_scanCurrentStack:
 
     // Restore stack state and return.
     add sp, #32
+    .cfi_def_cfa_offset 1*4
     pop {pc}
+    .cfi_endproc
+.size tinygo_scanCurrentStack, .-tinygo_scanCurrentStack

src/runtime/gc_avr.S

@@ -0,0 +1,52 @@
+.section .text.tinygo_scanCurrentStack
+.global tinygo_scanCurrentStack
+.type tinygo_scanCurrentStack, %function
+tinygo_scanCurrentStack:
+    // Save callee-saved registers.
+    push r29 // Y
+    push r28 // Y
+    push r17
+    push r16
+    push r15
+    push r14
+    push r13
+    push r12
+    push r11
+    push r10
+    push r9
+    push r8
+    push r7
+    push r6
+    push r5
+    push r4
+    push r3
+    push r2
+
+    // Scan the stack.
+    in  r24, 0x3d; SPL
+    in  r25, 0x3e; SPH
+#if __AVR_ARCH__ == 2 || __AVR_ARCH__ == 25
+    rcall tinygo_scanstack
+#else
+    call tinygo_scanstack
+#endif
+
+    // Restore callee-saved registers.
+    pop r2
+    pop r3
+    pop r4
+    pop r5
+    pop r6
+    pop r7
+    pop r8
+    pop r9
+    pop r10
+    pop r11
+    pop r12
+    pop r13
+    pop r14
+    pop r15
+    pop r16
+    pop r17
+    pop r28 // Y
+    pop r29 // Y

src/runtime/scheduler_avr.S

@@ -187,56 +187,3 @@ tinygo_switchToScheduler:
 
     // Return into the scheduler, as if tinygo_switchToTask was a regular call.
     ret
-
-.section .text.tinygo_scanCurrentStack
-.global tinygo_scanCurrentStack
-.type tinygo_scanCurrentStack, %function
-tinygo_scanCurrentStack:
-    // Save callee-saved registers.
-    push r29 // Y
-    push r28 // Y
-    push r17
-    push r16
-    push r15
-    push r14
-    push r13
-    push r12
-    push r11
-    push r10
-    push r9
-    push r8
-    push r7
-    push r6
-    push r5
-    push r4
-    push r3
-    push r2
-
-    // Scan the stack.
-    in  r24, 0x3d; SPL
-    in  r25, 0x3e; SPH
-#if __AVR_ARCH__ == 2 || __AVR_ARCH__ == 25
-    rcall tinygo_scanstack
-#else
-    call tinygo_scanstack
-#endif
-
-    // Restore callee-saved registers.
-    pop r2
-    pop r3
-    pop r4
-    pop r5
-    pop r6
-    pop r7
-    pop r8
-    pop r9
-    pop r10
-    pop r11
-    pop r12
-    pop r13
-    pop r14
-    pop r15
-    pop r16
-    pop r17
-    pop r28 // Y
-    pop r29 // Y

src/runtime/scheduler_cortexm.S

@@ -136,34 +136,3 @@ tinygo_swapTask:
     #endif
     .cfi_endproc
 .size tinygo_swapTask, .-tinygo_swapTask
-
-.section .text.tinygo_scanCurrentStack
-.global  tinygo_scanCurrentStack
-.type    tinygo_scanCurrentStack, %function
-tinygo_scanCurrentStack:
-    .cfi_startproc
-    // Save callee-saved registers onto the stack.
-    #if defined(__thumb2__)
-    push {r4-r11, lr}
-    .cfi_def_cfa_offset 9*4
-    #else
-    mov r0, r8
-    mov r1, r9
-    mov r2, r10
-    mov r3, r11
-    push {r0-r3, lr}
-    .cfi_def_cfa_offset 5*4
-    push {r4-r7}
-    .cfi_def_cfa_offset 4*4
-    #endif
-
-    // Scan the stack.
-    mov r0, sp
-    bl tinygo_scanstack
-
-    // Restore stack state and return.
-    add sp, #32
-    .cfi_def_cfa_offset 1*4
-    pop {pc}
-    .cfi_endproc
-.size tinygo_scanCurrentStack, .-tinygo_scanCurrentStack

targets/avr.json

@@ -13,6 +13,7 @@
 		"-Wl,--gc-sections"
 	],
 	"extra-files": [
+		"src/runtime/gc_avr.S",
 		"src/runtime/scheduler_avr.S"
 	]
 }

targets/cortex-m.json

@@ -25,6 +25,7 @@
 	],
 	"extra-files": [
 		"src/device/arm/cortexm.s",
+		"src/runtime/gc_arm.S",
 		"src/runtime/scheduler_cortexm.S"
 	],
 	"gdb": "gdb-multiarch"

targets/gameboy-advance.json

@@ -25,7 +25,7 @@
 	"linkerscript": "targets/gameboy-advance.ld",
 	"extra-files": [
 		"targets/gameboy-advance.s",
-		"src/runtime/scheduler_gba.S"
+		"src/runtime/gc_arm.S"
 	],
 	"gdb": "gdb-multiarch",
 	"emulator": ["mgba", "-3"]

targets/riscv.json

@@ -18,7 +18,7 @@
 	],
 	"extra-files": [
 		"src/device/riscv/start.S",
-		"src/runtime/scheduler_tinygoriscv.S",
+		"src/runtime/gc_riscv.S",
 		"src/device/riscv/handleinterrupt.S"
 	],
 	"gdb": "riscv64-unknown-elf-gdb"