x/tools/gopls: FoldingRange: corrupt g in slices.SortFunc

[adonovan]

#!stacks
"sigpanic" && "pdqsortCmpFunc" && "golang.FoldingRange"

Issue created by stacks.

This stack g1XUGA was reported by telemetry:

This is a corrupt g at the start of the call to pdqsortCmpFunc:

TEXT slices.pdqsortCmpFunc[...](SB) slices/zsortanyfunc.go
  zsortanyfunc.go:61    0x100987150             f9400b90                MOVD 16(R28), R16   <--- SEGV

• crash/crash
• runtime.throw:+9,+0x37
• runtime.sigpanic:+33,+0x223
• slices.pdqsortCmpFunc[...]:+0,+0x0
• slices.SortFunc[...]:=32,+0x243
• golang.org/x/tools/gopls/internal/golang.FoldingRange:+104,+0x20c
• golang.org/x/tools/gopls/internal/server.(*server).FoldingRange:+12,+0x1eb
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+313,+0x3407
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.ServerHandler.func4:+5,+0x73
• golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.handshaker.func5:+52,+0x68f
• golang.org/x/tools/gopls/internal/protocol.Handlers.MustReplyHandler.func1:+2,+0xbf
• golang.org/x/tools/gopls/internal/protocol.Handlers.AsyncHandler.func2.2:+3,+0x8f
• runtime.goexit:+0,+0x3

golang.org/x/tools/gopls@v0.19.1 go1.24.4 darwin/arm64 other,vscode (1)

[gabyhelp]

Related Issues

• x/tools/gopls: SEGV in HasSuffix (corrupt string) #74348
• x/tools/gopls: growslice crashes while zeroing #74932
• x/tools/gopls: corrupt g in printf.run #75232
• x/tools/gopls: "slice bounds out of range" crash in ExtractToNewFile #70553
• x/tools/gopls: sigpanic in methods of persistent.Map (corrupt g) #74870
• x/tools/gopls: automated issue report (crash) #40819 (closed)
• x/tools/gopls: CodeActions: "end < start" panic #74394 (closed)
• x/tools/gopls: nil deref in x/telemetry/internal/counter.(*Counter).add #73890
• x/tools/gopls: analysisinternal.ZeroValue crash on (presumably) unsafe.Pointer #70585 (closed)
• x/tools/gopls: Definition: crash on [unsafe.Pointer] doc link #74434 (closed)

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[jba]

Why do we think this is a gopls bug? How can gopls corrupt the runtime?

[adonovan]

Why do we think this is a gopls bug? How can gopls corrupt the runtime?

We know that gopls experiences a whole firehose of random g and SP corruption bugs, and we presume they are due to a misuse of unsafe (or a data race) that we have been unable to track down. It's possible the bug is in the GC or the scheduler, but we have no evidence, so I have been hesitant to cast aspersions on the runtime. That said, gopls is about the only program in the Go ecosystem that has crash telemetry, so it is possible that we're the only ones seeing these (infrequent) crashes because we're the only ones looking for them.