code review 8455043: runtime: poor man's heap type info checker

runtime: poor man's heap type info checker
It's not trivial to make a comprehensive check
due to inferior pointers, reflect, gob, etc.
But this is essentially what I've used to debug
the GC issues.
Update issue 5193.

[dvyukov, 2013-04-07 01:13:20]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://dvyukov%40google.com@code.google.com/p/go/

[iant, 2013-04-07 03:17:08]

LGTM

But it would be nice if somebody else looked at this too.

https://codereview.appspot.com/8455043/diff/5001/src/pkg/runtime/mgc0.c
File src/pkg/runtime/mgc0.c (right):

https://codereview.appspot.com/8455043/diff/5001/src/pkg/runtime/mgc0.c#newco...
src/pkg/runtime/mgc0.c:556: // Sanity check for the derived type info objti.
Add a comment that this is only used when Debug != 0.

https://codereview.appspot.com/8455043/diff/5001/src/pkg/runtime/mgc0.c#newco...
src/pkg/runtime/mgc0.c:573: x -=
(uintptr)(runtime·mheap->arena_start)>>PageShift;
Is there a tab missing at the start of this line?

[dvyukov, 2013-04-07 03:33:26]

https://codereview.appspot.com/8455043/diff/5001/src/pkg/runtime/mgc0.c
File src/pkg/runtime/mgc0.c (right):

https://codereview.appspot.com/8455043/diff/5001/src/pkg/runtime/mgc0.c#newco...
src/pkg/runtime/mgc0.c:556: // Sanity check for the derived type info objti.
On 2013/04/07 03:17:08, iant wrote:
> Add a comment that this is only used when Debug != 0.

Done.

https://codereview.appspot.com/8455043/diff/5001/src/pkg/runtime/mgc0.c#newco...
src/pkg/runtime/mgc0.c:573: x -=
(uintptr)(runtime·mheap->arena_start)>>PageShift;
On 2013/04/07 03:17:08, iant wrote:
> Is there a tab missing at the start of this line?

Done.

[dvyukov, 2013-04-08 18:00:13]

On 2013/04/07 03:17:08, iant wrote:
> LGTM
> 
> But it would be nice if somebody else looked at this too.

+atom, can you take a look?

[atom, 2013-04-08 18:19:38]

LGTM

[r, 2013-04-08 18:30:20]

LGTM but i think you want one more print statement

https://codereview.appspot.com/8455043/diff/10001/src/pkg/runtime/mgc0.c
File src/pkg/runtime/mgc0.c (right):

https://codereview.appspot.com/8455043/diff/10001/src/pkg/runtime/mgc0.c#newc...
src/pkg/runtime/mgc0.c:586: runtime·throw("invalid gc type info");
should you print more diagnostics here before throwing the state away?

[dvyukov, 2013-04-08 18:42:03]

https://codereview.appspot.com/8455043/diff/10001/src/pkg/runtime/mgc0.c
File src/pkg/runtime/mgc0.c (right):

https://codereview.appspot.com/8455043/diff/10001/src/pkg/runtime/mgc0.c#newc...
src/pkg/runtime/mgc0.c:586: runtime·throw("invalid gc type info");
On 2013/04/08 18:30:20, r wrote:
> should you print more diagnostics here before throwing the state away?

The problem is that these few variables won't provide any useful information.
FTR here is the reference to the debugging code that I actually used:
https://codereview.appspot.com/8517044
But it contains 400+ LOC of debugging code that print all sorts of information
about current block, referenced block, GC programs, allocation stacks with some
support from mprof, etc.
The main purpose of this CL is merely to detect a bug. Then somebody will need
to figure out how to debug it and what info he needs.

[r, 2013-04-08 18:42:59]

Fair enough. LGTM as is

[dvyukov, 2013-04-08 20:36:48]

*** Submitted as https://code.google.com/p/go/source/detail?r=e95933d23b2f ***

runtime: poor man's heap type info checker
It's not trivial to make a comprehensive check
due to inferior pointers, reflect, gob, etc.
But this is essentially what I've used to debug
the GC issues.
Update issue 5193.

R=golang-dev, iant, 0xe2.0x9a.0x9b, r
CC=golang-dev
https://codereview.appspot.com/8455043