exitsyscall: syscall frame is no longer valid

[Or Ricon]

Hi,

I'm encountering the following panic:

fatal error: exitsyscall: syscall frame is no longer valid
    runtime stack:
    runtime.throw(0xfacd50, 0x2d)
	$GOROOT/src/runtime/panic.go:596 +0x95
    runtime.exitsyscall.func1()
	$GOROOT/src/runtime/proc.go:2587 +0x36
    runtime.systemstack(0x7fc0ea7fbe88)
	$GOROOT/src/runtime/asm_amd64.s:327 +0x79
    runtime.mstart()
	$GOROOT/src/runtime/proc.go:1132
    goroutine 2857675810 [syscall, locked to thread]:
    runtime.cgocall(0xdfbe60, 0xc4370a51a8, 0xfaa4fd)
	$GOROOT/src/runtime/cgocall.go:131 +0xe2 fp=0xc4370a5168 sp=0xc4370a5128
    golua/lua._Cfunc_lua_pushlstring(0x7f7a9004ef60, 0x7fc0e0265490, 0xa)
	golua/lua/_obj/_cgo_gotypes.go:1154 +0x45 fp=0xc4370a51a8 sp=0xc4370a5168
    golua/lua.(*State).PushString.func2(0x7f7a9004ef60, 0x7fc0e0265490, 0xa)
	$GOPATH/golua/lua/lua.go:385 +0x74 fp=0xc4370a51e0 sp=0xc4370a51a8
    golua/lua.(*State).PushString(0xc4662b8240, 0xf8f104, 0xa)
	$GOPATH/golua/lua/lua.go:385 +0x89 fp=0xc4370a5210 sp=0xc4370a51e0
OMITTED	INTERNAL LIB
    golua/lua.golua_callgofunction(0xc4662b8240, 0x39, 0xc400000008)
	$GOPATH/golua/lua/golua.go:73 +0x6d fp=0xc4370a5290 sp=0xc4370a5240
    golua/lua._cgoexpwrap_cea3daa1dadf_golua_callgofunction(0xc4662b8240, 0x39, 0x38994071e5)
	golua/lua/_obj/_cgo_gotypes.go:1568 +0x35 fp=0xc4370a52b8 sp=0xc4370a5290
    runtime.call32(0x0, 0x7fc0ea7fba38, 0x7fc0ea7fbad0, 0x18)
	$GOROOT/src/runtime/asm_amd64.s:514 +0x48 fp=0xc4370a52e8 sp=0xc4370a52b8
    runtime.cgocallbackg1(0x0)
	$GOROOT/src/runtime/cgocall.go:301 +0x19d fp=0xc4370a5360 sp=0xc4370a52e8
    runtime.cgocallbackg(0x0)
	$GOROOT/src/runtime/cgocall.go:184 +0x84 fp=0xc4370a53c8 sp=0xc4370a5360
    created by net/http.(*Server).Serve
	$GOROOT/src/net/http/server.go:2668 +0x2ce

From my basic understanding of this I think it might be related to setjmp/longjmp calls after which cgo calls into Go, which based on your comments in #53 and in several other places I understand is not allowed.

I'm pretty fuzzy on the details but I realize it's somewhat similar to this issue (mitchellh/go-mruby#49) which is fixed in (mitchellh/go-mruby#50).

Would love to know if you have an idea of what causes this and of a possible fix.

[Alessandro Arzilli]

You should take a look at your calls to PushString. You are probably doing something to make it raise a lua exception. If you find out what that is we can put a guard in PushString and return an error.

You are right that this is related to the longjmp/setjmp stuff. I must say, for a language that's all about embedding, supposedly, sprinkling your interpreter with longjmps is not the best idea.

[Or Ricon]

This is a sample snippet, similar to the one where the panic occurs:

...
L.CreateTable(0, 0)
L.PushString("key")
L.PushString("value")
L.SetTable(-3)
...

It seems the panic will occur on either the call to CreateTable or PushString.
It would also seem that this only happens rarely and not on every invocation of the code.

[Alessandro Arzilli]

maybe you're out of memory? No clue.