gccgo: traceback should suppress frames with no debug info

[gopherbot]

by capnm9:

gccgo built from gcc tip:

commit f248394b138d19d68661563d4b6b5a22e3b12b18
Author: ian <ian@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Fri Aug 23 01:08:25 2013 +0000

    libgo: Update libtool.m4 from upstream to recognize powerpcle.

    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@201933 138bc75d-0d04-0410-961f-82ee72b054a4



E.g. divide by zero panic:

export GOTRACEBACK=2
./a.out
panic: runtime error: integer divide by zero

goroutine 1 [running]:
runtime_dopanic
    /data4/soft/go/gccgo-git/libgo/runtime/panic.c:71
__go_panic
    /data4/soft/go/gccgo-git/libgo/runtime/go-panic.c:113
runtime_panicstring
    /data4/soft/go/gccgo-git/libgo/runtime/panic.c:121
__go_runtime_error
    /data4/soft/go/gccgo-git/libgo/runtime/go-runtime-error.c:85

    :0
runtime_main
    /data4/soft/go/gccgo-git/libgo/runtime/proc.c:529
kickoff
    /data4/soft/go/gccgo-git/libgo/runtime/proc.c:229

    :0

goroutine 3 [runnable]:
kickoff
    /data4/soft/go/gccgo-git/libgo/runtime/proc.c:226

    :0
created by runtime_main
    /data4/soft/go/gccgo-git/libgo/runtime/proc.c:520

goroutine 4 [runnable]:
kickoff
    /data4/soft/go/gccgo-git/libgo/runtime/proc.c:226

    :0

goroutine 5 [runnable]:
kickoff
    /data4/soft/go/gccgo-git/libgo/runtime/proc.c:226

    :0

[gopherbot]

Comment 1 by capnm9:

+ In this panic it's generally missing a back-trace from main.main

[ianlancetaylor]

Comment 2:

It's not garbage, exactly, it's just not helpful.  The :0 indicates frames for which the
backtrace library couldn't find any debug info.  Most likely they are in libc.  The
backtrace library doesn't yet understand how to find separate debug info files.
Probably the fix should be, for a frame with no debug info, to just print the PC value.

Labels changed: added priority-later, gccgo, removed priority-triage.

[gopherbot]

Comment 3 by capnm9:

> The backtrace library doesn't yet understand how to find separate debug info files.
Ah yes, that could be a challenge.
I'm parsing the error outputs from both compilers/runtimes. I would certainly prefer to
have something at least looking useful or just nothing.
Sorry for the false alarm in the comment #1 I've forgotten the -g option, without it the
(here most helpful) main.main backtrace disappears.

[robpike]

Comment 4:

Changing the description.

Status changed to Accepted.

[rsc]

Comment 6:

Labels changed: added go1.3maybe.

[rsc]

Comment 7:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 8:

Labels changed: added repo-gccgo.