package main
import (
	"fmt"
	"sync/atomic"
)

// On ARM, x86-32, and 32-bit MIPS, it is the caller's responsibility to arrange for 64-bit alignment of 64-bit words accessed atomically.
// The first word in a variable or in an allocated struct, array, or slice can be relied upon to be 64-bit aligned.
func test(){
	x := struct {
		v uint64
		y uint32
	}{}
	
	fmt.Println()  //if comment this line, it will pass on 32-bit arch
	atomic.AddUint64(&x.v, 1)
}
func main() {
	test()
}

$ GOARCH=386 go build -ldflags=-compressdwarf=false -o test test.go
$ gdb ./hello
(gdb) b main.main
Thread 2 hit Breakpoint 1, main.main ()
    at /Dig101-Go/test.go:19
19      func main() {
(gdb) s
20              test()
(gdb) 
main.test () at /Dig101-Go/test.go:10
10      func test(){
(gdb) 
11              x := struct {
(gdb) 
runtime.newobject (typ=0x9d280 <type.*+93280>, ~r1=<optimized out>)
    at /usr/local/Cellar/go/1.13.7/libexec/src/runtime/malloc.go:1150
1150    func newobject(typ *_type) unsafe.Pointer {
(gdb) 
1151            return mallocgc(typ.size, typ, true)
(gdb) 
runtime.mallocgc (size=<optimized out>, typ=0x9d280 <type.*+93280>, needzero=true, 
    ~r3=<optimized out>)
    at /usr/local/Cellar/go/1.13.7/libexec/src/runtime/malloc.go:877
877     func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
(gdb) 
878             if gcphase == _GCmarktermination {
(gdb) until 945
runtime.mallocgc (size=<optimized out>, typ=0x9d280 <type.*+93280>, needzero=true, ~r3=<optimized out>)
    at /usr/local/Cellar/go/1.13.7/libexec/src/runtime/malloc.go:945
945             if size <= maxSmallSize {
(gdb) n
946                     if noscan && size < maxTinySize {
(gdb) 
976                             off := c.tinyoffset
(gdb) 
978                             if size&7 == 0 {
(gdb) 
980                             } else if size&3 == 0 {
(gdb) 
981                                     off = round(off, 4)
(gdb) 
985                             if off+size <= maxTinySize && c.tiny != 0 {
(gdb) p off
$1 = 4
(gdb) p c.tinyoffset  <========= notice this line
$2 = 2
(gdb) n
987                                     x = unsafe.Pointer(c.tiny + off)
(gdb) 
988                                     c.tinyoffset = off + size
(gdb) 
989                                     c.local_tinyallocs++
(gdb) 
990                                     mp.mallocing = 0
(gdb) 
991                                     releasem(mp)
(gdb) 
992                                     return x
(gdb) 
main.test () at /Dig101-Go/test.go:16
16              fmt.Println() 
(gdb) 

17              atomic.AddUint64(&x.v, 1)
(gdb) 

Thread 2 received signal SIGSEGV, Segmentation fault.
runtime/internal/atomic.Xadd64 () at /usr/local/Cellar/go/1.13.7/libexec/src/runtime/internal/atomic/asm_386.s:105
105             MOVL    0, AX // crash when unaligned
(gdb) 
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x2f7c]

goroutine 1 [running]:
runtime/internal/atomic.Xadd64(0x1141c0b4, 0x1, 0x0, 0x0, 0x0)
        /usr/local/Cellar/go/1.13.7/libexec/src/runtime/internal/atomic/asm_386.s:105 +0xc
main.test()
        /Dig101-Go/test.go:17 +0x72
main.main()
        /Dig101-Go/test.go:20 +0x11
[Inferior 1 (process 68214) exited with code 02]

$ ./test  # success

$ ./test # failed

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x2f7c]

goroutine 1 [running]:
runtime/internal/atomic.Xadd64(0x1147e004, 0x1, 0x0, 0x0, 0x0)
        /usr/local/Cellar/go/1.13.7/libexec/src/runtime/internal/atomic/asm_386.s:105 +0xc
main.test()
        /Dig101-Go/test.go:17 +0x72
main.main()
        /Dig101-Go/test.go:20 +0x11