cmd/compile: include registerization info for gdb

[ianlancetaylor]

What steps will reproduce the problem?

foo.go:

package main

import "os"

type I interface{}

func main() {
    var i I = 1
    os.Exit(i.(int))
}

6g foo.go
6l foo.6
gdb 6.out
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Reading symbols from /home/iant/gcc/gccgo2-objdir/6.out...done.
Loading Go Runtime support.
(gdb) break foo.go:9
Breakpoint 1 at 0x400c36: file /home/iant/foo1.go, line 9.
(gdb) run
Starting program: /home/iant/gcc/gccgo2-objdir/6.out 

Breakpoint 1, main.main () at /home/iant/foo1.go:9
9       os.Exit(i.(int))
(gdb) print i
No symbol "i" in current context.
(gdb) info locals
No locals.
(gdb) step
runtime.assertE2T (t=void, e=void) at /home/iant/go/src/pkg/runtime/iface.c:286
286 runtime·assertE2T(Type *t, Eface e, ...)
(gdb) finish
Run till exit from #0  runtime.assertE2T (t=void, e=void)
    at /home/iant/go/src/pkg/runtime/iface.c:286
0x0000000000400c4f in main.main () at /home/iant/foo1.go:9
9       os.Exit(i.(int))
(gdb) print i
No symbol "i" in current context.
(gdb) step
os.Exit (code=1) at /home/iant/go/src/pkg/os/proc.go:34
34  func Exit(code int) { syscall.Exit(code) }

What is the expected output?

I expect to see information about the local variable.

[rsc]

Comment 1:

Labels changed: added priority-later, removed priority-medium.

[rsc]

Comment 2:

Labels changed: added priority-go1.

[lvdlvd]

Comment 3:

This seems to happen for local variables that have been registerized completely, so that
their stack frame entry has been eliminated.   6nm shows no entry for 'i' in foo.6, nor
does it occur in 6g -S output.
then if it were present, the ld/dwarf code currently does not describe information about
registerized variables.
i'll think about the best way to pass both hurdles.

[rsc]

Comment 4:

If this is only about registerized variables then it can wait until after Go 1.
Nothing in the tool chain preserves that information.

Labels changed: added priority-later, removed priority-go1.

[rsc]

Comment 5:

Labels changed: added priority-someday, removed priority-later.

[rsc]

Comment 6:

Owner changed to @rsc.

[gopherbot]

Comment 7 by martin.kobetic@jadedpixel.com:

not seeing locals at all makes debugging quite difficult. Is there any workaround for
this? Anything better than disassembling the function and then trying to infer the
values directly from the registers?

[rsc]

Comment 8:

The usual workaround is print statements.

[rsc]

Comment 9:

Labels changed: added repo-main.

[rsc]

Comment 10:

Adding Release=None to all Priority=Someday bugs.

Labels changed: added release-none.

[rsc]

Comment 11:

Issue #7659 has been merged into this issue.