code review 13774043: runtime: avoid allocation of internal panic values

runtime: avoid allocation of internal panic values

If a fault happens in malloc, inevitably the next thing that happens
is a deadlock trying to allocate the panic value that says the fault
happened. Stop doing that, two ways.

First, reject panic in malloc just as we reject panic in garbage collection.

Second, runtime.panicstring was using an error implementation
backed by a Go string, so the interface held an allocated *string.
Since the actual errors are C strings, define a new error
implementation backed by a C char*, which needs no indirection
and therefore no allocation.

This second fix will avoid allocation for errors like nil panic derefs
or division by zero, so it is worth doing even though the first fix
should take care of faults during malloc.

Update issue 6419

[rsc, 2013-09-19 04:11:20]

Hello golang-dev@googlegroups.com,

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

[dvyukov, 2013-09-19 04:18:55]

LGTM

[dfc, 2013-09-19 04:47:19]

On 2013/09/19 04:18:55, dvyukov wrote:
> LGTM

Thanks rsc. I hope that this will also help with issue 5594. I am trying to
build a new freebsd/arm system to validate this.

[rsc, 2013-09-20 19:15:33]

*** Submitted as https://code.google.com/p/go/source/detail?r=02f28778ccb9 ***

runtime: avoid allocation of internal panic values

If a fault happens in malloc, inevitably the next thing that happens
is a deadlock trying to allocate the panic value that says the fault
happened. Stop doing that, two ways.

First, reject panic in malloc just as we reject panic in garbage collection.

Second, runtime.panicstring was using an error implementation
backed by a Go string, so the interface held an allocated *string.
Since the actual errors are C strings, define a new error
implementation backed by a C char*, which needs no indirection
and therefore no allocation.

This second fix will avoid allocation for errors like nil panic derefs
or division by zero, so it is worth doing even though the first fix
should take care of faults during malloc.

Update issue 6419

R=golang-dev, dvyukov, dave
CC=golang-dev
https://codereview.appspot.com/13774043