avr: drop GNU toolchain dependency

- Use compiler-rt and picolibc instead of avr-libc.
  - Use ld.lld instead of avr-ld (or avr-gcc).

This makes it much easier to get started with TinyGo on AVR because
installing these extra tools (gcc-avr, avr-libc) can be a hassle.
It also opens the door for future improvements such as ThinLTO.

There is a code size increase but I think it's worth it in the long run.
The code size increase can hopefully be reduced with improvements to the
LLVM AVR backend and to compiler-rt.

.circleci/config.yml

@@ -63,8 +63,6 @@ commands:
                 clang-<<parameters.llvm>> \
                 libclang-<<parameters.llvm>>-dev \
                 lld-<<parameters.llvm>> \
-                gcc-avr \
-                avr-libc \
                 cmake \
                 ninja-build
       - hack-ninja-jobs

.github/workflows/build-macos.yml

@@ -93,7 +93,7 @@ jobs:
           path: build/tinygo.darwin-amd64.tar.gz
       - name: Smoke tests
         shell: bash
-        run: make smoketest TINYGO=$(PWD)/build/tinygo AVR=0
+        run: make smoketest TINYGO=$(PWD)/build/tinygo
   test-macos-homebrew:
     name: homebrew-install
     runs-on: macos-latest

.github/workflows/linux.yml

@@ -133,11 +133,6 @@ jobs:
           mkdir -p ~/lib
           tar -C ~/lib -xf tinygo.linux-amd64.tar.gz
           ln -s ~/lib/tinygo/bin/tinygo ~/go/bin/tinygo
-      - name: Install apt dependencies
-        run: |
-          sudo apt-get install --no-install-recommends \
-              gcc-avr \
-              avr-libc
       - run: make tinygo-test-wasi-fast
       - run: make smoketest
   assert-test-linux:
@@ -158,8 +153,6 @@ jobs:
               qemu-system-arm \
               qemu-system-riscv32 \
               qemu-user \
-              gcc-avr \
-              avr-libc \
               simavr \
               ninja-build
       - name: Install Go

.github/workflows/windows.yml

@@ -125,7 +125,7 @@ jobs:
         run: 7z x release.zip -r
       - name: Smoke tests
         shell: bash
-        run: make smoketest TINYGO=$(PWD)/build/tinygo/bin/tinygo AVR=0
+        run: make smoketest TINYGO=$(PWD)/build/tinygo/bin/tinygo
 
   stdlib-test-windows:
     runs-on: windows-2022

Dockerfile

@@ -2,7 +2,7 @@
 FROM golang:1.19 AS tinygo-llvm
 
 RUN apt-get update && \
-    apt-get install -y apt-utils make cmake clang-11 binutils-avr gcc-avr avr-libc ninja-build
+    apt-get install -y apt-utils make cmake clang-11 ninja-build
 
 COPY ./Makefile /tinygo/Makefile
 

Makefile

@@ -674,7 +674,6 @@ ifneq ($(STM32), 0)
 	$(TINYGO) build -size short -o test.hex -target=swan                examples/blinky1
 	@$(MD5SUM) test.hex
 endif
-ifneq ($(AVR), 0)
 	$(TINYGO) build -size short -o test.hex -target=atmega1284p         examples/serial
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=arduino             examples/blinky1
@@ -693,7 +692,6 @@ ifneq ($(AVR), 0)
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=digispark -gc=leaking examples/blinky1
 	@$(MD5SUM) test.hex
-endif
 ifneq ($(XTENSA), 0)
 	$(TINYGO) build -size short -o test.bin -target=esp32-mini32      	examples/blinky1
 	@$(MD5SUM) test.bin

builder/builtins.go

@@ -162,6 +162,15 @@ var aeabiBuiltins = []string{
 	"udivmodsi4.c",
 }
 
+var avrBuiltins = []string{
+	"avr/divmodhi4.S",
+	"avr/divmodqi4.S",
+	"avr/mulhi3.S",
+	"avr/mulqi3.S",
+	"avr/udivmodhi4.S",
+	"avr/udivmodqi4.S",
+}
+
 // CompilerRT is a library with symbols required by programs compiled with LLVM.
 // These symbols are for operations that cannot be emitted with a single
 // instruction or a short sequence of instructions for that target.
@@ -186,6 +195,9 @@ var CompilerRT = Library{
 		if strings.HasPrefix(target, "arm") || strings.HasPrefix(target, "thumb") {
 			builtins = append(builtins, aeabiBuiltins...)
 		}
+		if strings.HasPrefix(target, "avr") {
+			builtins = append(builtins, avrBuiltins...)
+		}
 		return builtins, nil
 	},
 }

builder/picolibc.go

@@ -78,7 +78,7 @@ var picolibcSources = []string{
 	"libc/tinystdio/fputc.c",
 	"libc/tinystdio/fputs.c",
 	"libc/tinystdio/fread.c",
-	"libc/tinystdio/freopen.c",
+	//"libc/tinystdio/freopen.c", // crashes with AVR, see: https://github.com/picolibc/picolibc/pull/369
 	"libc/tinystdio/fscanf.c",
 	"libc/tinystdio/fseek.c",
 	"libc/tinystdio/fseeko.c",

src/runtime/arch_avr.go

@@ -37,3 +37,39 @@ func procPin() {
 func procUnpin() {
 	interrupt.Restore(procPinnedMask)
 }
+
+// The following functions are workarounds for things missing in compiler-rt.
+// They will likely need special assembly implementations.
+
+//export __mulsi3
+func __mulsi3(a, b uint32) uint32 {
+	var r uint32
+	for a != 0 {
+		if a&1 != 0 {
+			r += b
+		}
+		a >>= 1
+		b <<= 1
+	}
+	return r
+}
+
+//export __divsi3
+func __divsi3(a, b int32) int32
+
+//export __udivsi3
+func __udivsi3(a, b uint32) uint32
+
+//export __divmodsi4
+func __divmodsi4(a, b int32) uint64 {
+	d := __divsi3(a, b)
+	rem := a - (d * b)
+	return uint64(uint32(d)) | uint64(uint32(rem))<<32
+}
+
+//export __udivmodsi4
+func __udivmodsi4(a, b uint32) uint64 {
+	d := __udivsi3(a, b)
+	rem := a - (d * b)
+	return uint64(d) | uint64(rem)<<32
+}

targets/arduino-mega1280.json

@@ -2,7 +2,7 @@
     "inherits": ["atmega1280"],
     "build-tags": ["arduino_mega1280"],
     "ldflags": [
-        "-Wl,--defsym=_bootloader_size=4096"
+        "--defsym=_bootloader_size=4096"
     ],
     "flash-command":"avrdude -c arduino -b 57600 -p atmega1280 -P {port} -U flash:w:{hex}:i -v -D"
 }

targets/arduino-mega2560.json

@@ -2,7 +2,7 @@
     "inherits": ["atmega2560"],
     "build-tags": ["arduino_mega2560"],
     "ldflags": [
-        "-Wl,--defsym=_bootloader_size=8192"
+        "--defsym=_bootloader_size=8192"
     ],
     "flash-command":"avrdude -c wiring -b 115200 -p atmega2560 -P {port} -U flash:w:{hex}:i -v -D"
 }

targets/arduino-nano.json

@@ -2,8 +2,8 @@
 	"inherits": ["atmega328p"],
 	"build-tags": ["arduino_nano"],
 	"ldflags": [
-		"-Wl,--defsym=_bootloader_size=512",
-		"-Wl,--defsym=_stack_size=512"
+		"--defsym=_bootloader_size=512",
+		"--defsym=_stack_size=512"
 	],
 	"flash-command": "avrdude -c arduino -p atmega328p -b 57600 -P {port} -U flash:w:{hex}:i",
 	"emulator": "simavr -m atmega328p -f 16000000 {}"

targets/arduino.json

@@ -2,8 +2,8 @@
 	"inherits": ["atmega328p"],
 	"build-tags": ["arduino"],
 	"ldflags": [
-		"-Wl,--defsym=_bootloader_size=512",
-		"-Wl,--defsym=_stack_size=512"
+		"--defsym=_bootloader_size=512",
+		"--defsym=_stack_size=512"
 	],
 	"flash-command": "avrdude -c arduino -p atmega328p -P {port} -U flash:w:{hex}:i",
 	"serial-port": ["2341:0043", "2341:0001", "2a03:0043", "2341:0243"],

targets/atmega1280.json

@@ -4,8 +4,7 @@
     "build-tags": ["atmega1280", "atmega"],
     "serial": "uart",
     "ldflags": [
-        "-mmcu=avr51",
-        "-Wl,--defsym=_stack_size=512"
+        "--defsym=_stack_size=512"
     ],
     "linkerscript": "src/device/avr/atmega1280.ld",
     "extra-files": [

targets/atmega1284p.json

@@ -4,9 +4,8 @@
     "build-tags": ["atmega1284p", "atmega"],
     "serial": "uart",
     "ldflags": [
-        "-mmcu=avr51",
-        "-Wl,--defsym=_bootloader_size=0",
-        "-Wl,--defsym=_stack_size=512"
+        "--defsym=_bootloader_size=0",
+        "--defsym=_stack_size=512"
     ],
     "linkerscript": "src/device/avr/atmega1284p.ld",
     "extra-files": [

targets/atmega2560.json

@@ -4,8 +4,7 @@
     "build-tags": ["atmega2560", "atmega"],
     "serial": "uart",
     "ldflags": [
-        "-mmcu=avr6",
-        "-Wl,--defsym=_stack_size=512"
+        "--defsym=_stack_size=512"
     ],
     "linkerscript": "src/device/avr/atmega2560.ld",
     "extra-files": [

targets/atmega328p.json

@@ -3,9 +3,6 @@
 	"cpu": "atmega328p",
 	"build-tags": ["atmega328p", "atmega", "avr5"],
 	"serial": "uart",
-	"ldflags": [
-		"-mmcu=avr5"
-	],
 	"linkerscript": "src/device/avr/atmega328p.ld",
 	"extra-files": [
 		"targets/avr.S",

targets/attiny85.json

@@ -5,9 +5,6 @@
 	"cflags": [
 		"-D__AVR_ARCH__=25"
 	],
-	"ldflags": [
-		"-mmcu=avr25"
-	],
 	"linkerscript": "src/device/avr/attiny85.ld",
 	"extra-files": [
 		"targets/avr.S",

targets/avr.json

@@ -4,16 +4,17 @@
 	"goos": "linux",
 	"goarch": "arm",
 	"gc": "conservative",
-	"linker": "avr-gcc",
+	"linker": "ld.lld",
 	"scheduler": "none",
 	"rtlib": "compiler-rt",
+	"libc": "picolibc",
 	"default-stack-size": 256,
 	"cflags": [
 		"-Werror"
 	],
 	"ldflags": [
 		"-T", "targets/avr.ld",
-		"-Wl,--gc-sections"
+		"--gc-sections"
 	],
 	"extra-files": [
 		"src/internal/task/task_stack_avr.S",

targets/avr.ld

@@ -5,6 +5,8 @@ MEMORY
     RAM (xrw)       : ORIGIN = 0x800000 + __ram_start, LENGTH = __ram_size
 }
 
+ENTRY(__vector_RESET)
+
 SECTIONS
 {
     .text :
@@ -12,9 +14,11 @@ SECTIONS
         KEEP(*(.vectors))
         KEEP(*(.text.__vector_RESET))
         KEEP(*(.text.main)) /* main must follow the reset handler */
+        *(.text)
         *(.text.*)
         *(.progmem)
         *(.progmem.*)
+        . = ALIGN(16); /* needed with ld.lld for some reasoon */
     }
 
     .stack (NOLOAD) :

targets/digispark.json

@@ -2,8 +2,8 @@
 	"inherits": ["attiny85"],
 	"build-tags": ["digispark"],
 	"ldflags": [
-		"-Wl,--defsym=_bootloader_size=2180",
-		"-Wl,--defsym=_stack_size=128"
+		"--defsym=_bootloader_size=2180",
+		"--defsym=_stack_size=128"
 	],
 	"flash-command": "micronucleus --run {hex}",
 	"emulator": "simavr -m attiny85 -f 16000000 {}"

tools/gen-device-avr/gen-device-avr.go

@@ -432,7 +432,7 @@ __vector_default:
 .endm
 
 ; The interrupt vector of this device. Must be placed at address 0 by the linker.
-.section .vectors
+.section .vectors, "a", %progbits
 .global  __vectors
 `))
 	err = t.Execute(out, device.metadata)