x/debug/cmd/viewcore: panic on go1.12

[pwaller]

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

$ go version
go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

• Increase my ulimit for corefiles
• Write a program with the line var foo *int; *foo = 1 to make it crash.
• Run program with GOTRACEBACK=crash to produce file called core.
• Run viewcore core.

What did you expect to see?

viewcore core should work. It does work with go1.11.5.

What did you see instead?

$ viewcore core --exe=./crasher
panic: bad int32 type uint8

goroutine 1 [running]:
golang.org/x/debug/internal/gocore.region.Int32(0xc0002de000, 0x62ba77, 0xc0000c0b90, 0x8b122b)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/region.go:82 +0xc6
golang.org/x/debug/internal/gocore.(*module).readFunc(0xc0002e3b90, 0xc0002de000, 0x62ba50, 0xc00056aa00, 0xc0002de000, 0x6e22c0, 0xc000366280, 0xc0000c0140)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/module.go:72 +0x4a0
golang.org/x/debug/internal/gocore.(*Process).readModule(0xc0002de000, 0xc0002de000, 0x6e22c0, 0xc000377180, 0x6e22c0)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/module.go:45 +0x4d4
golang.org/x/debug/internal/gocore.(*Process).readModules(0xc0002de000)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/module.go:26 +0x1a6
golang.org/x/debug/internal/gocore.Core(0xc00011c000, 0x4, 0x0, 0x0)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/process.go:155 +0x2be
main.readCore(0x8af649, 0x4, 0xc0000b6e68, 0x4)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/cmd/viewcore/main.go:260 +0xd5
main.runRoot(0xc48ea0, 0xc00007ad50, 0x0, 0x1)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/cmd/viewcore/main.go:282 +0x45
github.com/spf13/cobra.(*Command).execute(0xc48ea0, 0xc0000201a0, 0x1, 0x1, 0xc48ea0, 0xc0000201a0)
	/home/pwaller/.local/pkg/mod/github.com/spf13/[email protected]/command.go:766 +0x2ae
github.com/spf13/cobra.(*Command).ExecuteC(0xc48ea0, 0x8af083, 0x1, 0xc0000dbf00)
	/home/pwaller/.local/pkg/mod/github.com/spf13/[email protected]/command.go:852 +0x2c0
github.com/spf13/cobra.(*Command).Execute(...)
	/home/pwaller/.local/pkg/mod/github.com/spf13/[email protected]/command.go:800
main.main()
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/cmd/viewcore/main.go:238 +0xba

/cc @randall77 @aclements

[pwaller]

I've bisected part of the breakage to 7b9c2c1: internal/cpu: add and use cpu.CacheLinePad for padding structs.

That commit results in the following stacktrace:

panic: address 205400051f4e0 is not mapped in the core file

goroutine 1 [running]:
golang.org/x/debug/internal/core.(*Process).ReadUint64(0xc00011c000, 0x205400051f4e0, 0x8af8f3)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/core/read.go:81 +0x264
golang.org/x/debug/internal/core.(*Process).ReadUintptr(0xc00011c000, 0x205400051f4e0, 0x40db88)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/core/read.go:120 +0x62
golang.org/x/debug/internal/gocore.region.Uintptr(0xc0004a6000, 0x205400051f4e0, 0xc0000c01e0, 0x8af8f3)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/region.go:40 +0x52
golang.org/x/debug/internal/gocore.(*module).readFunc(0xc00076af90, 0xc0004a6000, 0x205400051f4e0, 0xc00052c6e0, 0xc0004a6000, 0x5961c0, 0xc00029aff0, 0xc0000c01e0)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/module.go:60 +0xdc
golang.org/x/debug/internal/gocore.(*Process).readModule(0xc0004a6000, 0xc0004a6000, 0x5961c0, 0xc00029af00, 0x5961c0)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/module.go:45 +0x4d4
golang.org/x/debug/internal/gocore.(*Process).readModules(0xc0004a6000)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/module.go:26 +0x1a6
golang.org/x/debug/internal/gocore.Core(0xc00011c000, 0x4, 0x0, 0x0)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/internal/gocore/process.go:155 +0x2be
main.readCore(0x3, 0x3, 0xc00008c4b0, 0xc00000e440)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/cmd/viewcore/main.go:260 +0xd5
main.runMappings(0xc49360, 0xc6de98, 0x0, 0x0)
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/cmd/viewcore/main.go:389 +0x37
github.com/spf13/cobra.(*Command).execute(0xc49360, 0xc6de98, 0x0, 0x0, 0xc49360, 0xc6de98)
	/home/pwaller/.local/pkg/mod/github.com/spf13/[email protected]/command.go:766 +0x2ae
github.com/spf13/cobra.(*Command).ExecuteC(0xc48ea0, 0x8af083, 0x1, 0xc0000dbf00)
	/home/pwaller/.local/pkg/mod/github.com/spf13/[email protected]/command.go:852 +0x2c0
github.com/spf13/cobra.(*Command).Execute(...)
	/home/pwaller/.local/pkg/mod/github.com/spf13/[email protected]/command.go:800
main.main()
	/home/pwaller/.local/pkg/mod/golang.org/x/[email protected]/cmd/viewcore/main.go:238 +0xba

[bcmills]

CC @martisch @bradfitz

[gopherbot]

Change https://golang.org/cl/170863 mentions this issue: cmd/gopherbot: CC triaged issues to owners

[gopherbot]

Change https://golang.org/cl/175497 mentions this issue: internal/gocore: update to handle 1.12 core files