code review 4222043: runtime: omit breakpoint during terminal panic

runtime: omit breakpoint during terminal panic

A terminal panic (one that prints a stack trace and exits)
has been calling runtime.breakpoint before calling exit,
so that if running under a debugger, the debugger can
take control.  When not running under a debugger, though,
this causes an additional SIGTRAP on Unix and pop-up
dialogs on Windows.

Support for debugging Go programs has gotten good
enough that we can rely on the debugger to set its own
breakpoint on runtime.exit if it wants to look around.

[rsc, 2011-02-23 19:54:58]

Hello r (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg

[r2, 2011-02-23 20:39:52]

LGTM

[rsc, 2011-02-23 20:42:17]

*** Submitted as 618f3bf36698 ***

runtime: omit breakpoint during terminal panic

A terminal panic (one that prints a stack trace and exits)
has been calling runtime.breakpoint before calling exit,
so that if running under a debugger, the debugger can
take control.  When not running under a debugger, though,
this causes an additional SIGTRAP on Unix and pop-up
dialogs on Windows.

Support for debugging Go programs has gotten good
enough that we can rely on the debugger to set its own
breakpoint on runtime.exit if it wants to look around.

R=r, r2
CC=golang-dev
http://codereview.appspot.com/4222043

[brainman, 2011-02-24 01:43:19]

On 2011/02/23 19:54:58, rsc wrote:
> Hello r (cc: mailto:golang-dev@googlegroups.com),
> 
> I'd like you to review this change to
> https://go.googlecode.com/hg

I don't think it is correct. This program:

package main

func main() {
        b := 0
        a := 10 / b
        println(a)
}

prints this:

panic: runtime error: integer divide by zero

[signal 0x8 code=0x1 addr=0x8048c24 pc=0x8048c24]

runtime.panic+0xa4 /root/hg/go/src/pkg/runtime/proc.c:1054
        runtime.panic(0x8056d78, 0x18478008)
runtime.panicstring+0x95 /root/hg/go/src/pkg/runtime/runtime.c:118
        runtime.panicstring(0x806b774, 0x8053059)
runtime.sigpanic+0x10c /root/hg/go/src/pkg/runtime/linux/thread.c:297
        runtime.sigpanic()
main.main+0x24 /root/t2/test.go:5
        main.main()
runtime.mainstart+0xf /root/hg/go/src/pkg/runtime/386/asm.s:93
        runtime.mainstart()
runtime.goexit /root/hg/go/src/pkg/runtime/proc.c:150
        runtime.goexit()

But runtime.panic calls runtime.dopanic, that calls runtime.breakpoint before
calling runtime.exit(2).

Alex