A compatibility bug on ARM V7

[zxxf18]

Describe the bug
Run time.Sleep(ws.backoff.Duration()) \\ ws.backoff != nil in arm v7 get a runtime error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x11e34]

goroutine 51 [running]:
runtime/internal/atomic.goXadd64(0x3db8bcc, 0x1, 0x0, 0x3ea8000, 0x3e9a5e8)
	/usr/local/go/src/runtime/internal/atomic/atomic_arm.go:103 +0x1c
github.com/jpillora/backoff.(*Backoff).Duration(0x3db8bcc, 0xf20220, 0x1cbc5c8)
	/go/pkg/mod/github.com/jpillora/backoff@v1.0.0/backoff.go:30 +0x30

Environment:

• Infrastructure: on raspberry pi (arm32v7)
• version: github.com/jpillora/backoff v1.0.0
• go version: 1.13

Analyze:

• The details of what operating system (specifically that it was 32bit) were key here to figuring this one out!
• Note, this has to be defined first to make sure it is aligned properly for 32bit ARM OS
• From https://golang.org/pkg/sync/atomic/#pkg-note-BUG
• On ARM, 386, 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.

[jpillora]

Can you try with go 1.17?

…

On Wed, 29 Dec 2021 at 5:41 pm zhaoxin ***@***.***> wrote: *Describe the bug* Run time.Sleep(ws.backoff.Duration()) \\ ws.backoff != nil in arm v7 get a runtime error: panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x11e34] goroutine 51 [running]: runtime/internal/atomic.goXadd64(0x3db8bcc, 0x1, 0x0, 0x3ea8000, 0x3e9a5e8) /usr/local/go/src/runtime/internal/atomic/atomic_arm.go:103 +0x1cgithub.com/jpillora/backoff.(*Backoff).Duration(0x3db8bcc, 0xf20220, 0x1cbc5c8) ***@***.***/backoff.go:30 +0x30 *Environment:* Infrastructure: on raspberry pi (arm32v7) version: github.com/jpillora/backoff v1.0.0 go version: 1.13 *Analyze:* The details of what operating system (specifically that it was 32bit) were key here to figuring this one out! Note, this has to be defined first to make sure it is aligned properly for 32bit ARM OS From https://golang.org/pkg/sync/atomic/#pkg-note-BUG On ARM, 386, 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. — Reply to this email directly, view it on GitHub <#17>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAE2X42OAYS24EZQZDIFFSTUTKUQNANCNFSM5K5MJMSQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[zxxf18]

In go1.17.5, this problem still exists.
https://golang.org/pkg/sync/atomic/#pkg-note-BUG
This is not a must-have problem, it sometimes works normally.

[ykholm]

"@jpillora Our team is using go 1.18, and our QA caught this error after building the service for GOOS=linux GOARCH=arm GOARM=7.

Here is the panic stack trace:

time="2023-05-20T12:26:05-05:00" level=error msg="App error" APP=gateway ERR="panic: unaligned 64-bit atomic operation
goroutine 82 [running]:
runtime/internal/atomic.panicUnaligned()
  /usr/local/go/src/runtime/internal/atomic/unaligned.go:8 +0x24
  runtime/internal/atomic.Store64(0x1691d4c, 0x0)
  /usr/local/go/src/runtime/internal/atomic/atomic_arm.s:291 +0x14
github.com/jpillora/backoff.(*Backoff).Reset(...)
  /src/build/go/pkg/mod/github.com/jpillora/backoff@v1.0.0/backoff.go:84."

I must mention that we have previously encountered this issue in our own code, and we resolved it by using an appropriate atomic operation for 32-bit processors: atomic.StoreUint32(&b.attempt, 0) instead of atomic.StoreUint64(&b.attempt, 0).

This fork has already made this change.

[AlekSi]

https://pkg.go.dev/sync/atomic#pkg-note-BUG says:

On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange for 64-bit alignment of 64-bit words accessed atomically via the primitive atomic functions