Turning off optimization and inlining in Go gc compilers for debugging.

.gdbinit

source /usr/local/go/src/pkg/runtime/runtime-gdb.py
b main.main

README.md

Turning off optimization and inlining in Go gc compilers

Pass the flags -gcflags '-N -l'.

$ go build -gcflags '-N -l' [code.go]

or

$ go install -gcflags '-N -l' [code.go]

References

• http://code.google.com/p/go/issues/detail?id=3363
• https://groups.google.com/forum/?fromgroups#!topic/golang-nuts/6m8bZYik8Ss

gdb_output1.txt

$ ls
README.md	sum.go
$ go build sum.go
$ ~/local/bin/gdb sum
GNU gdb (GDB) 7.4.1
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin11.4.0".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /Users/tetsuo-s/github/gist-3025333/sum...done.
Loading Go Runtime support.
Breakpoint 1 at 0x202f: file /Users/tetsuo-s/github/gist-3025333/sum.go, line 13.
(gdb) l
1	package main
2
3	import "fmt"
4
5	func sum(n int) int {
6		sum := 0
7		for i := 1; i < n; i++ {
8			sum += i
9		}
10		return sum
(gdb) r
Starting program: /Users/tetsuo-s/github/gist-3025333/sum
[New Thread 0x1e03 of process 23269]
[Switching to Thread 0x1e03 of process 23269]

Breakpoint 1, main.main () at /Users/tetsuo-s/github/gist-3025333/sum.go:13
13	func main() {
(gdb) n
14		n := sum(10) // n should be 45
(gdb) n
15		fmt.Printf("sum = %d\n", n)
(gdb) p n
No symbol "n" in current context.
(gdb) c
Continuing.
sum = 45
[Inferior 1 (process 23269) exited normally]
(gdb)

gdb_output2.txt

$ go build -gcflags '-N -l' sum.go
$ ~/local/bin/gdb sum
GNU gdb (GDB) 7.4.1
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin11.4.0".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /Users/tetsuo-s/github/gist-3025333/sum...done.
Loading Go Runtime support.
Breakpoint 1 at 0x2055: file /Users/tetsuo-s/github/gist-3025333/sum.go, line 13.
(gdb) l
1	package main
2
3	import "fmt"
4
5	func sum(n int) int {
6		sum := 0
7		for i := 1; i < n; i++ {
8			sum += i
9		}
10		return sum
(gdb) r
Starting program: /Users/tetsuo-s/github/gist-3025333/sum
[New Thread 0x1e03 of process 23362]
[Switching to Thread 0x1e03 of process 23362]

Breakpoint 1, main.main () at /Users/tetsuo-s/github/gist-3025333/sum.go:13
13	func main() {
(gdb) n
14		n := sum(10) // n should be 45
(gdb) n
15		fmt.Printf("sum = %d\n", n)
(gdb) p n
$1 = 45
(gdb)

inspect_register.txt

$ ~/local/bin/gdb sum
GNU gdb (GDB) 7.4.1
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin11.4.0".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /Users/tetsuo-s/github/gist-3025333/sum...done.
Loading Go Runtime support.
Breakpoint 1 at 0x202f: file /Users/tetsuo-s/github/gist-3025333/sum.go, line 13.
(gdb) l
1	package main
2
3	import "fmt"
4
5	func sum(n int) int {
6		sum := 0
7		for i := 1; i < n; i++ {
8			sum += i
9		}
10		return sum
(gdb) l
11	}
12
13	func main() {
14		n := sum(10) // n should be 45
15		fmt.Printf("sum = %d\n", n)
16	}
(gdb) r
Starting program: /Users/tetsuo-s/github/gist-3025333/sum
[New Thread 0x1e03 of process 23634]
[Switching to Thread 0x1e03 of process 23634]

Breakpoint 1, main.main () at /Users/tetsuo-s/github/gist-3025333/sum.go:13
13	func main() {
(gdb) s
14		n := sum(10) // n should be 45
(gdb) x/5i $rip
=> 0x2046 <main.main+23>:	mov    DWORD PTR [rsp],0xa
   0x204d <main.main+30>:	call   0x2000 <main.sum>
   0x2052 <main.main+35>:	mov    ecx,DWORD PTR [rsp+0x8]
   0x2056 <main.main+39>:	lea    rdi,[rsp+0x48]
   0x205b <main.main+44>:	xor    rax,rax
(gdb) p $ecx
$1 = 1108488192
(gdb) ni
0x000000000000204d	14		n := sum(10) // n should be 45
(gdb) ni
0x0000000000002052	14		n := sum(10) // n should be 45
(gdb) x/i $rip
=> 0x2052 <main.main+35>:	mov    ecx,DWORD PTR [rsp+0x8]
(gdb) ni
15		fmt.Printf("sum = %d\n", n)
(gdb) p $ecx
$2 = 45
(gdb)

sum.go

package main

import "fmt"

func sum(n int) int {
	sum := 0
	for i := 1; i < n; i++ {
		sum += i
	}
	return sum
}

func main() {
	n := sum(10) // n should be 45
	fmt.Printf("sum = %d\n", n)
}

I believe the current incantation is

-gcflags 'all=-N -l'

When I left out all= I and debugged using dlv, I got the warning that I was debugging optimized functions.

To debug using dlv I use:

dlv test --build-flags="-gcflags 'all=-N -l'"

and if I need to debug as root:

sudo -E --preserve-env=PATH bash -c "dlv test --build-flags=\"-gcflags 'all=-N -l'\""