go/types: SEGV in tpWalker.isParameterized, case Signature

[adonovan]

#!stacks
"sigpanic" && "go/types.(*tpWalker).isParameterized:+45"

Issue created by stacks.

The failing source line is:

	case *Signature:
		// t.tparams may not be nil if we are looking at a signature
		// of a generic function type (or an interface method) that is
		// part of the type we're testing. We don't care about these type
		// parameters.
		// Similarly, the receiver of a method may declare (rather than
		// use) type parameters, we don't care about those either.
		// Thus, we only need to look at the input and result parameters.
		return t.params != nil && w.varList(t.params.vars) || t.results != nil && w.varList(t.results.vars) // <-- SEGV

The assembly shows that it is a load of t.params (field offset 32) that fails, indicating that t is an invalid pointer (either nil or garbage caused by a soft error):

TEXT go/types.(*tpWalker).isParameterized(SB) go
lang.org/toolchain@v0.0.1-go1.26.2.darwin-arm64/src/go/types/infer.go
  infer.go:561          0x1003def50             f9400b90                MOVD 16(R28), R16                               
...
  infer.go:576          0x1003df0e8             140000f6                JMP 246(PC)                                     
  infer.go:598          0x1003df0ec             b000a325                ADRP 21385216(PC), R5                           
  infer.go:598          0x1003df0f0             9101c0a5                ADD $112, R5, R5                                
  infer.go:598          0x1003df0f4             eb05007f                CMP R5, R3                                      
  infer.go:598          0x1003df0f8             54000f21                BNE 121(PC)                                     
->infer.go:606          0x1003df0fc             f9401043                MOVD 32(R2), R3 ; load t.params (SEGV) 
  infer.go:606          0x1003df100             b40000c3                CBZ R3, 6(PC)                                   
  infer.go:606          0x1003df104             a9401063                LDP (R3), (R3, R4)                              
  infer.go:606          0x1003df108             f90023e4                MOVD R4, 64(RSP)                                

This stack Rfu6uA was reported by telemetry:

• crash/crash
• runtime.gopanic:+70,+0x15b
• go/types.(*Checker).handleBailout:+25,+0x93
• go/types.(*Checker).Files.deferwrap1:+0,+0x1f
• runtime.gopanic:+51,+0x12b
• runtime.panicmem:=336,+0x2ef
• runtime.sigpanic:+19,+0x2c0
• go/types.(*tpWalker).isParameterized:+45,+0x1ac
• go/types.(*tpWalker).isParameterized:+15,+0x573
• go/types.(*tpWalker).varList:=644,+0x50f
• go/types.(*tpWalker).isParameterized:+45,+0x1ac
• go/types.(*tpWalker).isParameterized:+15,+0x573
• go/types.(*tpWalker).varList:=644,+0x50f
• go/types.(*tpWalker).isParameterized:+45,+0x1ac
• go/types.(*tpWalker).isParameterized:+15,+0x573
• go/types.(*tpWalker).varList:=644,+0x50f
• go/types.(*tpWalker).isParameterized:+45,+0x1ac
• go/types.(*tpWalker).isParameterized:+15,+0x573
• go/types.(*tpWalker).varList:=644,+0x50f
• go/types.(*tpWalker).isParameterized:+45,+0x1ac
• go/types.isParameterized:=553,+0x967
• go/types.(*Checker).infer:+258,+0x8ac
• go/types.(*Checker).arguments:+152,+0x8d3

golang.org/x/tools/gopls@v0.21.1 go1.26.2 darwin/arm64 gopls.client=other (1)

Use this command to reproduce the executable:
(HOME=$(mktemp -d); GOOS=darwin GOARCH=arm64 GOTOOLCHAIN=go1.26.2 go install golang.org/x/tools/gopls@v0.21.1 && find $HOME/go/bin -type f)
To disassemble: go tool objdump exe | less

[gabyhelp]

Related Issues

• x/tools/gopls: types.isString crashes in MOV reg,reg instruction #77920 (closed)
• x/tools/gopls: SEGV in (*types.*Checker).Ident due to nil or invalid *ast.Ident in syntax tree #77078 (closed)
• x/tools/gopls: SEGV loading m.used field from non-nil map pointer (in types.Scope.elems map) #76979 (closed)
• go/types, types2: gopls crash on method with type parameters #50427 (closed)
• x/tools/gopls: impossible panic reading rtype.hash in type assertion #76328 (closed)
• x/tools/gopls: impossible panic in BlockStmt.End (type checking IfStmt with nil Body) #76327 (closed)
• x/tools/gopls: SEGV in go/types due to invalid pointer in BinaryExpr.Y #76238 (closed)
• go/types, types2: panic with "unexpected *types.Tuple" in isParameterized #59890 (closed)
• go/types: alias TypeName has nil typ #77321
• x/tools/gopls: failed assertion in go/types.validType0 #78042

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}