CODEWITHSUNDEEP
pythongogdb
chmurson
chmurson

Reputation: 619

golang gdb - print variables

I have a problem with gdb not printing variables correctly. Simple program is build in following way:

chmurson-osx:helloworld chmurson$ go build -gcflags '-N' start.go

And then gdb executed:

chmurson-osx:helloworld chmurson$ gdb start -d $GOROOT
GNU gdb (GDB) 7.8
Copyright (C) 2014 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-darwin14.0.0".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from start...done.
warning: Missing auto-load scripts referenced in section .debug_gdb_scripts
of file /Users/chmurson/Dev/goprojects/misc/src/helloworld/start
Use `info auto-load python-scripts [REGEXP]' to list them.
(gdb) 
(gdb) source /usr/local/go/src/pkg/runtime/runtime-gdb.py
Loading Go Runtime support.

Here is what I do next:

(gdb) list
1   package main
2   
3   import "fmt"
4   
5   func main() {
6       x := "abc"
7       i := 3
8       fmt.Println(i)
9       fmt.Println(x)
10  }
(gdb) b 9
Breakpoint 1 at 0x2106: file /Users/chmurson/Dev/goprojects/misc/src/helloworld/start.go, line 9.
(gdb) run
Starting program: /Users/chmurson/Dev/goprojects/misc/src/helloworld/start 
3
[New Thread 0x1113 of process 14039]

Breakpoint 1, main.main () at /Users/chmurson/Dev/goprojects/misc/src/helloworld/start.go:9
9       fmt.Println(x)
(gdb) p x
Python Exception <type 'exceptions.OverflowError'> signed integer is greater than maximum: 
$1 = 
(gdb) p i
$2 = 8725692800
(gdb)

You can see that there is Python Exception on examination of 'p' variable, and totally not 3 when displaying value of 'i'. What's wrong ?

Here is my go version

chmurson-osx:helloworld chmurson$ go version
go version go1.3.1 darwin/amd64

And gdb configuration

(gdb) show configuration
This GDB was configured as follows:
   configure --host=x86_64-apple-darwin14.0.0 --target=x86_64-apple-darwin14.0.0
             --with-auto-load-dir=:${prefix}/share/auto-load
             --with-auto-load-safe-path=:${prefix}/share/auto-load
             --with-expat
             --with-gdb-datadir=/usr/local/share/gdb (relocatable)
             --with-jit-reader-dir=/usr/local/lib/gdb (relocatable)
             --without-libunwind-ia64
             --without-lzma
             --with-python=/System/Library/Frameworks/Python.framework/Versions/2.7
             --without-guile
             --with-separate-debug-dir=/usr/local/lib/debug (relocatable)
             --with-zlib
             --without-babeltrace

("Relocatable" means the directory can be moved with the GDB installation
tree, and GDB will still find it.)

Upvotes: 4

Views: 1718

Answers (2)

OneOfOne
OneOfOne

Reputation: 99274

Adding to @AlexAtNet's answer, everything after Go 1.2.x breaks GDB support, so either use go 1.2.x for debugging or use gccgo (keep in mind that gcc 4.8.x supports go 1.1, gcc 4.9.x is up to 1.2).

Another option is to use your own trace function, not pretty but it's currently the only real debug option for go 1.3+.

I personally use something like this for debugging:

var traceLock sync.Mutex

func trace(a ...interface{}) {
    traceLock.Lock()
    pc, f, ln, ok := runtime.Caller(1)
    fn := ""
    if ok {
        fn = runtime.FuncForPC(pc).Name()
    }
    fmt.Printf("trace: %s %s:%d", fn, filepath.Base(f), ln)
    if len(a) > 0 {
        fmt.Println(append([]interface{}{": "}, a...)...)
    }
    traceLock.Unlock()
}

playground

Upvotes: 2

Alex Netkachov
Alex Netkachov

Reputation: 13532

The GDB support is not a priority for the Go team so it is unlikely that the number of such issues will be fixed soon. Consider the following:

https://golang.org/doc/gdb

GDB does not understand Go programs well. The stack management, threading, and runtime contain aspects that differ enough from the execution model GDB expects that they can confuse the debugger, even when the program is compiled with gccgo. As a consequence, although GDB can be useful in some situations, it is not a reliable debugger for Go programs, particularly heavily concurrent ones. Moreover, it is not a priority for the Go project to address these issues, which are difficult.

However, you can use the Gccgo toolchain and successfully debug the go programs. However, installing it on a Mac is a bit cumbersome.

Upvotes: 2

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