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wgengine/magicsock: add more docs, checks to Test32bitAlignment

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Per recent chat with @raggi about all this, I went and looked at this
test again.

Updates #cleanup

Change-Id: Icb7d87b1ed2cebf481ee4e358a3aa603e63fb8a4
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2026-05-06 06:30:15 -07:00 committed by Brad Fitzpatrick
parent 15bb10dbce
commit d06cc56987
1 changed files with 19 additions and 2 deletions
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21
wgengine/magicsock/magicsock_test.go
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@ -1460,7 +1460,20 @@ func TestDiscoStringLogRace(t *testing.T) {
wg.Wait()
}
// Test32bitAlignment verifies that that the 64-bit atomic mono.Time fields are
// 64-bit aligned, so that StoreAtomic and LoadAtomic won't panic on 32-bit
// platforms.
//
// For normal Go atomic types (sync/atomic.Int64, etc), the Go compiler
// guarantees 64-bit alignment on 32-bit platforms with an unexported magic
// embedded struct field. We can't make mono.Time use that easily. We could change
// mono.Time to be type Time struct { atomic.Int64 }, but that's pretty invasive.
// Instead, we just have this test to keep us safe on 32-bit platforms.
func Test32bitAlignment(t *testing.T) {
if rt := reflect.TypeFor[mono.Time](); rt.Kind() != reflect.Int64 {
t.Fatalf("mono.Time is not a 64-bit integer type anymore; this test may be irrelevant now or out of date")
}
de := endpoint{
c: &Conn{},
}
@ -1468,9 +1481,13 @@ func Test32bitAlignment(t *testing.T) {
if off := unsafe.Offsetof(de.lastRecvWG); off%8 != 0 {
t.Fatalf("endpoint.lastRecvWG is not 8-byte aligned")
}
if off := unsafe.Offsetof(de.lastRecvUDPAny); off%8 != 0 {
t.Fatalf("endpoint.lastRecvUDPAny is not 8-byte aligned")
}
de.noteRecvActivity(epAddr{}, mono.Now()) // verify this doesn't panic on 32-bit
de.noteRecvActivity(epAddr{}, mono.Now()) // second call should be throttled
// Verify these don't panic.
de.lastRecvWG.StoreAtomic(mono.Now())
de.lastRecvUDPAny.StoreAtomic(mono.Now())
}
// newTestConn returns a new Conn.