endpointdiscovery.Endpointcache will panic on 32-bit archs

[dswarbrick]

Describe the bug

atomic.panicUnaligned will occur due to unaligned struct member size. This occurs since the size of the endpoints sync.Map is variable, depending on the machine word size. On 64-bit archs, sync.Map is 32 bytes. On 32-bit archs, sync.Map is 20 bytes - resulting in the misalignment of the subsequent members in the EndpointCache struct:

type EndpointCache struct {
    endpoints     sync.Map
    endpointLimit int64
    // size is used to count the number elements in the cache.
    // The atomic package is used to ensure this size is accurate when
    // using multiple goroutines.
    size int64
}

$ GOARCH=386 go run foo.go 
size of EndpointCache.endpoints: 20
offset of EndpointCache.endpoints: 0
offset of EndpointCache.endpointLimit: 20
offset of EndpointCache.size: 28
panic: unaligned 64-bit atomic operation

goroutine 1 [running]:
runtime/internal/atomic.panicUnaligned()
        /usr/lib/go-1.21/src/runtime/internal/atomic/unaligned.go:8 +0x2d
runtime/internal/atomic.Xadd64(0x9ca201c, 0x1)
        /usr/lib/go-1.21/src/runtime/internal/atomic/atomic_386.s:125 +0x11
main.main()
        /tmp/foo/foo.go:30 +0x1e6
exit status 2

Expected Behavior

No panic to occur.

Current Behavior

The following test fails on 32-bit archs:

=== RUN   TestEndpointCache_Get_prune
--- FAIL: TestEndpointCache_Get_prune (0.00s)
panic: unaligned 64-bit atomic operation [recovered]
        panic: unaligned 64-bit atomic operation

goroutine 6 [running]:
testing.tRunner.func1.2({0x81c33c0, 0x822a528})
        /usr/lib/go-1.21/src/testing/testing.go:1545 +0x2ab
testing.tRunner.func1()
        /usr/lib/go-1.21/src/testing/testing.go:1548 +0x43e
panic({0x81c33c0, 0x822a528})
        /usr/lib/go-1.21/src/runtime/panic.go:914 +0x1ec
runtime/internal/atomic.panicUnaligned()
        /usr/lib/go-1.21/src/runtime/internal/atomic/unaligned.go:8 +0x2d
runtime/internal/atomic.Xadd64(0xa0140dc, 0x1)
        /usr/lib/go-1.21/src/runtime/internal/atomic/atomic_386.s:125 +0x11
github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery.(*EndpointCache).Add(0xa0140c0, {{0x81eb800, 0x3}, {0xa0140f0, 0x2, 0x2}})
        /home/daniel/Work/Debian/golang-github-aws-aws-sdk-go-v2/service/internal/endpoint-discovery/cache.go:76 +0xd1
github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery.TestEndpointCache_Get_prune(0xa1280f0)
        /home/daniel/Work/Debian/golang-github-aws-aws-sdk-go-v2/service/internal/endpoint-discovery/cache_test.go:11 +0x25b
testing.tRunner(0xa1280f0, 0x81fda70)
        /usr/lib/go-1.21/src/testing/testing.go:1595 +0x120
created by testing.(*T).Run in goroutine 1
        /usr/lib/go-1.21/src/testing/testing.go:1648 +0x3dd
FAIL    github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery        0.004s
FAIL

Reproduction Steps

Force test to execute as a 32-bit GOARCH, e.g.

GOARCH=386 go test ./...

Possible Solution

Reorder the struct members so that the size member, which is used in atomic operations, is 64-bit aligned.

Additional Information/Context

No response

AWS Go SDK V2 Module Versions Used

github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery github.com/aws/[email protected]
github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery github.com/aws/[email protected]
github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery [email protected]
github.com/aws/[email protected] github.com/aws/[email protected]
github.com/aws/[email protected] github.com/google/[email protected]
github.com/aws/[email protected] github.com/jmespath/[email protected]
github.com/aws/[email protected] github.com/google/[email protected]

Compiler and Version used

go version go1.21.1 linux/amd64

Operating System and version

Linux xps15 6.5.0-21-generic #21-Ubuntu SMP PREEMPT_DYNAMIC Wed Feb 7 14:17:40 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux

[github-actions]

This issue is now closed. Comments on closed issues are hard for our team to see.
If you need more assistance, please open a new issue that references this one.