How to debug fatal error: unexpected signal during runtime execution ?

[Eric Z]

Hello Golang-Nuts,

I am writing a go program calling c library and function. It works fluently in some cases, but sometime it exit with error code 2.

However the error printout starts with a long list of go routines at crash. This gives me no clue how to debug. Can some one give some advice? Thanks a lot.

fatal error: unexpected signal during runtime execution
[signal 0xb code=0x1 addr=0x0 pc=0x0]
runtime stack:
runtime.throw(0x863885)
      /usr/local/go/src/pkg/runtime/panic.c:520 +0x69 fp=0x7fa2c0df9c28 sp=0x7fa2c0df9c10
 runtime: unexpected return pc for runtime.sigpanic called from 0x4098a5
 runtime.sigpanic()
    /usr/local/go/src/pkg/runtime/os_linux.c:222 +0x3d fp=0x7fa2c0df9c40 sp=0x7fa2c0df9c28



Cheers,
Eric

[Andrew Gerrand]

You'll need to show more of the stacks. Usually the first stack trace is for the responsible goroutine.

Are you calling into multi-threaded C code? I've seen that cause this particular error.

Andrew

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[Eric Z]

Thanks for taking a quick look.

The first goroutine looks like this. It still gives me no clue. It is a single thread c program. However, two go routines might be calling it at the same time.

goroutine 560 [syscall]:
runtime.cgocall(0x403820, 0x7fa2c01db918)
        /usr/local/go/src/pkg/runtime/cgocall.c:143 +0xe5 fp=0x7fa2c01db900 sp=0x7fa2c01db8b8
main._Cfunc_encoder(0x200000005, 0x64000000005, 0xcf22551000, 0xcf12d981c0, 0xca9b45f8fc, 0xcba710a8fc, 0x18)
        mycode/_obj/_cgo_defun.c:66 +0x36 fp=0x7fa2c01db918 sp=0x7fa2c01db900
main.encoder_core(0x7fa2c01dbe18, 0x1, 0x1, 0xca9b45f8fc, 0x22551000, 0x13b4df904, 0xcba710a8fc, 0xdbba000, 0x2f834904, 0xcd950dc020, ...)
        /home/eric.z/git/src/mycode/encoder.go:391 +0x2bc fp=0x7fa2c01dbaf0 sp=0x7fa2c01db918
main.encoder(0x6, 0xcd950ca5a0, 0xcd950dc020, 0x1, 0x1, 0x5, 0xcdc4cdc1d8, 0xc2080542a0, 0xcd94e81380, 0xcdc4cde300)
        /home/eric.z/git/src/mycode/encoder.go:460 +0xa7f fp=0x7fa2c01dbf58 sp=0x7fa2c01dbaf0
runtime.goexit()
        /usr/local/go/src/pkg/runtime/proc.c:1445 fp=0x7fa2c01dbf60 sp=0x7fa2c01dbf58
created by main.destination
        /home/eric.z/git/src/mycode/main.go:1493 +0x1243

[Dave Cheney]

Hi Eric,

Looks like there was a nil pointer dereference in your C code. Can you please make the _entire_ panic message available somewhere, possibly pastebin if you don't want to attach it here.

Dave

[Eric Z]

Thanks a million.

Here is the 3k line error track
http://pastebin.com/gNPE87kA

How did you tell it's a nil pointer dereference? It's pretty hard for me to understand the panic message. I am wondering if there's some tool to parse or blog post to teach on what to read.

[Dave Cheney]

Code 0x0b is 11, which is SIGSEGV. addr=0x0, which is nil/null in most
programming languages.

main.encoder_core(0x7fa2c01dbe18, 0x1, 0x1, 0xca9b45f8fc, 0x22551000,
0x13b4df904, 0xcba710a8fc, 0xdbba000, 0x2f834904, 0xcd950dc020, ...)

What are the arguments to this function ?

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[Eric Z]

Thank you Dave. This is very helpful. Let me add some code to check all pointers to be valid.

encoder_core calls the C function

func encoder_core(info []E2ASstruct, data []byte, coding []byte, e2as []chan E2ASstruct, disk_lock *sync.Mutex, page int, i_disk int, send_pending bool) bool

[Dave Cheney]

Nothing obvious there, info is a slice of one value, data is a heap
allocated structure sliced out of a larger slice, the slice of
channels is odd, i'm not sure if the stack trace is showing the full
list of arguments to that function.

At this point all I can suggest is there is a bug in whatever code
you're calling via cgo.

[Eric Z]

Thanks Dave.

I am following your advice, and it does seem that the error comes from one the libraries the c code calls. It's sill pretty hard to track. Stack trace seems to be limited on indicating exactly which c code throws the error.

[eviefe...@gmail.com]

hello!I got this problem in my program too ,do you konw how to solve this multi-threaded C code problem?

在 2014年9月16日星期二 UTC+8上午7:20:16，Andrew Gerrand写道：

[Chaitanya Kapre]

Same issue found while doing multi threading in C. It runs fine when single thread is there but fails for multithread. Did you know how to implement multi threading in C python with golang integratiion?