Comment 1 by esko.luontola:

The functions symtab.c:/^funcline and extern.go:/FileLine appear to have comments, that 
if you edit one of them, you should edit also the other. The code looks too cryptic for 
me to tell whether the two functions do the same thing or not.
Somebody should add an automated test which makes sure that both of the functions do 
the same thing, to avoid the implementations from drifting apart. Even better would be 
to implement one of them by calling the other - that would remove the duplicated code.

Comment 2:

Status changed to Accepted.

Comment 3 by StepLg:

It seems, that the bug is around here:
runtime/extern.go: func (f *Func) FileLine(pc uintptr)
const PcQuant = 1
because in symtab.c:/^funcline there is:
    int32 pcquant;
    switch(thechar) {
    case '5':
        pcquant = 4;
        break;
    default:    // 6, 8
        pcquant = 1;
        break;
    }
i found, that 'thechar' is information about compiler:
$GO/src/pkg/runtime% grep -r thechar .
./amd64/arch.h: thechar = '6'
./386/arch.h:   thechar = '8'
./arm/arch.h:   thechar = '5'
but i don't know how to get the same info in go

Comment 4 by StepLg:

and another difference:
in symtab.c:/^funcline
} else if(*p <= 128) {
    line -= *p - 64;
}
and in runtime/extern.go: func (f *Func) FileLine(pc uintptr)
case p[i] <= 128:
    line += int(p[i] - 64)

Comment 5:

Verified that this bug is now fixed.
I believe it was 
changeset:   6158:523da6275fc6
user:        Russ Cox <rsc@golang.org>
date:        Thu Sep 02 14:19:12 2010 -0400
summary:     runtime: add GOOS, GOARCH; fix FuncLine

Status changed to Fixed.

Comment 6 by esko.luontola:

I found an off-by-one in the line numbers reported by FuncLine(). I've reported it as a
separate issue: https://golang.org/issue/1100
I still think that the best solution would be to refactor the code to remove the code
duplication between extern.go and symtab.c. That would eliminate one "bug breeding
ground" as mentioned in http://jamesshore.com/Agile-Book/no_bugs.html Now that same
copy-pasted function has resulted already in two bugs.