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cmd/compile: compiler segfaults in cmd/compile/internal/gc.markUsedIfaceMethod #45258

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parabolala opened this issue Mar 26, 2021 · 7 comments
Closed

cmd/compile: compiler segfaults in cmd/compile/internal/gc.markUsedIfaceMethod #45258

parabolala opened this issue Mar 26, 2021 · 7 comments
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FrozenDueToAge NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.

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@parabolala
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What version of Go are you using (go version)?

$ go version
go version go1.16.2 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jenia/Library/Caches/go-build"
GOENV="/Users/jenia/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/jenia/go/pkg/mod"
GONOPROXY="..."
GONOSUMDB="..."
GOOS="darwin"
GOPATH="/Users/jenia/go"
GOPRIVATE="..."
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/local/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/local/lib/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16.2"
GCCGO="gccgo"
AR="ar"
CC="/usr/bin/clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/tmp/worker/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/nk/w186v63s5kz_vcwvlt7t2rc40000gn/T/go-build489409122=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://play.golang.org/p/TGtWALJVzT9

What did you expect to see?

Program compiles

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x40 pc=0xb8c31d]

goroutine 1 [running]:
cmd/internal/obj.Addrel(...)
	/usr/local/go/src/cmd/internal/obj/data.go:195
cmd/compile/internal/gc.markUsedIfaceMethod(0xc0003b0a00)
	/usr/local/go/src/cmd/compile/internal/gc/walk.go:1625 +0x7d
cmd/compile/internal/gc.walkexpr(0xc0003b0a00, 0xc0000c34a8, 0x0)
	/usr/local/go/src/cmd/compile/internal/gc/walk.go:559 +0x3c79
cmd/compile/internal/gc.walkstmt(0xc0003b0a00, 0xc0003cc980)
	/usr/local/go/src/cmd/compile/internal/gc/walk.go:149 +0xd0b
cmd/compile/internal/gc.walkstmtlist(0xc0003c8580, 0x7, 0x8)
	/usr/local/go/src/cmd/compile/internal/gc/walk.go:81 +0x47
cmd/compile/internal/gc.walk(0xc0000a69a0)
	/usr/local/go/src/cmd/compile/internal/gc/walk.go:65 +0x3bd
cmd/compile/internal/gc.compile(0xc0000a69a0)
	/usr/local/go/src/cmd/compile/internal/gc/pgen.go:239 +0x85
cmd/compile/internal/gc.funccompile(0xc0000a69a0)
	/usr/local/go/src/cmd/compile/internal/gc/pgen.go:220 +0xc5
cmd/compile/internal/gc.Main(0xcc7d40)
	/usr/local/go/src/cmd/compile/internal/gc/main.go:762 +0x3525
main.main()
	/usr/local/go/src/cmd/compile/main.go:52 +0xb1

Note: this seems specific to the function name _. If I rename similar function to a proper function name, the code compiles (unless like in example here where it needs to be main to compile).
@ALTree
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ALTree commented Mar 27, 2021

Similar issue reported in the past: #29870.

Anyway this seems to be fixed on tip. Go 1.15 is also not affected.

cc @randall77 for a decision about Go 1.16.

@ALTree ALTree added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Mar 27, 2021
@ALTree ALTree changed the title Compiler segfaults in cmd/compile/internal/gc.markUsedIfaceMethod cmd/compile: compiler segfaults in cmd/compile/internal/gc.markUsedIfaceMethod Mar 27, 2021
@cuonglm
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cuonglm commented Apr 18, 2021

This bug was introduced in 39dde09, which use Curfn.Func.lsym unconditionally. For function name _, Curfn.Func.lsym is nil. The bug exists because for function name _, we don't generate code but still walk through it.

This was partially fixed in cc90e7a, since when we don't walk through function name _ anymore.

I think the right fix, is making reflectdata.MarkUsedIfaceMethod handle function name _ correctly. Though, It does not affect the functionality of the compiler at tip (because we only call reflectdata.MarkUsedIfaceMethod during walk), it makes shipping a backport to 1.16 more easily.

cc @cherrymui @mdempsky @randall77

@randall77
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I don't think this needs a backport fix for 1.16. There is a trivial workaround (don't use _ as the function name).

This was partially fixed in cc90e7a, since when we don't walk through function name _ anymore.

Does tip still need a fix? I'm confused by the "partial" part of that statement.

@cuonglm
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cuonglm commented Apr 18, 2021

@randall77 commit cc90e7a make function name _ isn't walked anymore, so the bug is disappear at tip, because reflectdata.MarkUsedIfaceMethod is only called during walk.

If it's called in other phases, e.g during typecheck, the bug is triggered again.

@randall77
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If it's called in other phases, e.g during typecheck, the bug is triggered again.

So does that ever happen?

@cuonglm
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cuonglm commented Apr 18, 2021

If it's called in other phases, e.g during typecheck, the bug is triggered again.

So does that ever happen?

No, at current tip.

@gopherbot
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Change https://golang.org/cl/311130 mentions this issue: cmd/compile: skip "_" function in reflectdata.MarkUsedIfaceMethod

@golang golang locked and limited conversation to collaborators Apr 19, 2022
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@parabolala @ALTree @cuonglm @randall77 @gopherbot