Comparing C and Go

Marcin Pasinski
Mender.io
Develop your Embedded Applications Faster:
Comparing C and Golang

My view on C vs Go
● I think Go is great and very
productive programming language
● It excels when developing
networking code
● I’m not considering it a
replacement or competitor for C
● Among the other things garbage
collection alone ensures that

Who am I?
● Marcin Pasinski
○ 10+ years in software development
○ M. Sc., Electronics and Telecommunication
○ marcin.pasinski@northern.tech
■ OTA updater for Linux devices
■ Integrated with Yocto
■ Open source (Apache v2 license)
■ Written in Go
■ Configuration management tool
■ Open source (GPL v3 license)
■ Written in C

Agenda
● Why did we choose go
● Go basics for Embedded development
● Code samples
● Demo

Language requirements
1. “External impact”
○ Size requirements on device
○ Setup requirement in Yocto Project
○ Possibility to compile for multiple platforms
2. “Internal considerations”
○ Competences in the company
○ Code share/reuse
○ Development speed
○ Access to common libraries (JSON, SSL, HTTP)
○ “Automatic memory management”
○ “Security enablers” (buffer overflow protection, etc.)

Language comparison
C C++ Go
Size requirements in devices Lowest Low (1.8MB more) Low (2.1 MB more, however will increase
with more binaries)
Setup requirements in Yocto None None Requires 1 layer (golang)*
Competence in the company Good Have some long time users Only couple of people know it
Buffer under/overflow protection None Little Yes
Code reuse/sharing from CFEngine Good Easy (full backwards compatibility) Can import C API
Automatic memory management No Available, but not enforced Yes
Standard data containers No Yes Yes
JSON json-c jsoncpp Built-in
HTTP library curl curl Built-in
SSL OpenSSL OpenSSL Built-in
* Go is natively supported by Yocto Project from Pyro release (Yocto 2.3)

Yocto build comparison
C C++ C++/Qt Go ...
Pure image size 8.4MB 10.2MB 20.8MB* 14.6MB
Size with network stack 13.4MB
(curl)
15.2MB
(curl)
20.8MB* 14.6MB
Shared dependencies Yes Yes Yes No/Maybe
Extra Yocto layer needed No No Yes Yes**
Deployment complexity Binary Binary Binary + Qt Binary
* Required some changes to upstream Yocto layer
** Go is natively supported by Yocto from Pyro release (Yocto 2.3)

Why did we pick up Go?
1. Golang has lots of core language features and libraries that allows much faster
development of applications.
2. The learning curve from C to Golang is very low, given the similarities in the language
structure.
3. As it is a compiled language, Golang runs natively on embedded devices.
4. Go is statically linked into a single binary, with no dependencies or libraries required at
the device (note that this is true for applications compiled with CGO_ENABLED=0).
5. Go provides wide platform coverage for cross-compilation to support different
architectures
6. Similar in size with static C binaries, Go binaries continue to get smaller as their compilers
get optimized.
7. Both the client and the backend are written in the same language

Go vs C: size
● gcc main.c
○ 8,5K
● ldd a.out
○ linux-vdso.so.1
○ libc.so.6
○ /lib64/ld-linux-x86-64.so.2
● gcc -static main.c
○ 892K
● gcc -static main.c & strip
○ 821K
package main
func main() {
println("hello world")
}
#include <stdio.h>
int main(void)
{
printf("hello worldn");
return 0;
}● $ go build
○ 938K
● $ go build -ldflags ‘-s -w’
○ 682K
● $ go build & strip
○ 623K
package main
import “fmt”
func main() {
fmt.Println("hello world")
}
● $ go build
○ 1,5M

Go vs C: speed
1. Go is fully garbage-collected
2. Go declaration syntax says nothing about stack and heap allocations making
those implementation dependant ($ go build -gcflags -m; )
3. Fast compilation
4. Go provides support for concurrent execution and communication
5. The speed of developer is most important in most cases and Go really excels
here
https://benchmarksgame-team.pages.debian.net/benchmarksgame/faster/go-gcc.html

Compilation
● Compilers
○ The original gc, the Go compiler, was written in C
○ As of Go 1.5 the compiler is written in Go with a recursive descent parser
and uses a custom loader, based on the Plan 9 loader
○ gccgo (frontend for GCC; https://golang.org/doc/install/gccgo)
■ gcc 7 supports Go 1.8.1
● Compilation
○ fast (large modules compiled within seconds)
○ single binary file (no dependencies, no virtual machines)
■ from Go 1.5 possible to create shared libraries and dynamic linking but
only on x86 architecture
○ makefile
(https://github.com/mendersoftware/mender/blob/master/Makefile)

Cross compilation (https://golang.org/doc/install/source#environment)
$GOOS / $GOARCH amd64 386 arm arm64 ppc64le ppc64 mips64le mips64 mipsle mips
android X
darwin X X X
dragonfly X
freebsd X X X
linux X X X X X X X X X X
netbsd X X X
openbsd X X X
plan9 X X
solaris X
windows X X

Debugging
● Gdb
● Delve (https://github.com/derekparker/delve)

C code inside Go
● CGO (https://golang.org/cmd/cgo/)
○ allows Go to access C library
functions and global variables
○ imported C functions are
available under virtual C
package
○ CGO_ENABLED
○ There is a cost associated with
calling C APIs (~150ns on Xeon
processor)
/*
#cgo LDFLAGS: -lpcap
#include <stdlib.h>
#include <pcap.h>
*/
import "C"
func getDevice() (string, error) {
var errMsg string
cerr := C.CString(errMsg)
defer C.free(unsafe.Pointer(cerr))
cdev := C.pcap_lookupdev(cerr)
dev := C.GoString(cdev)
return dev, nil
}

C++ code inside go
● SWIG
○ Simplified Wrapper and
Interface Generator
○ Used to create wrapper code
to connect C and C++ to other
languages
○ http://www.swig.org/Doc2.0/
Go.html
// helloclass.cpp
std::string HelloClass::hello(){
return "world";
}
// helloclass.h
class HelloClass
{
public:
std::string hello();
}
// mylib.swig
%module mylib
%{
#include "helloclass.h"
%}

Shared Go libraries
● Possible from Go 1.5
○ -buildmode argument
■ archive
■ c-archive
■ c-shared
■ shared
■ exe
● ~ go build -buildmode=shared -o
myshared
● ~ go build -linkshared -o app
myshared
// package name: mygolib
package main
import "C"
import "fmt"
//export SayHiElc
func SayHiElc(name string) {
fmt.Printf("Hello ELC: %s!n", name)
}
func main() {
// We need the main for Go to
// compile C shared library
}

Shared C libraries
● ~ go build -buildmode=c-shared -o
mygolib.a mygolib.go
● ~ gcc -o myapp myapp.c mygolib.a
// mygolib.h
typedef signed char GoInt8;
typedef struct { char *p; GoInt n; }
GoString;
extern void SayHiElc(GoString p0);
// myapp.c
#include "mygolib.h"
#include <stdio.h>
int main() {
printf("Go from C app.n");
GoString name = {"Prague", 6};
SayHiElc(name);
return 0;
}

Embedded Go
● Heap vs stack
○ go build -gcflags -m
○ ./main.go:17: msg escapes to
heap
● Unsafe code
○ C: *(uint8_t*)0x1111 = 0xFF;
○ Manipulating hardware
directly is possible with GO,
but it has been made
intentionally cumbersome.
file, _ := os.OpenFile("/dev/gpiomem",
os.O_RDWR|os.O_SYNC, 0);
mem, _ := syscall.Mmap(int(file.Fd()),
0x20000000, 4096,
syscall.PROT_READ|syscall.PROT_WRITE,
syscall.MAP_SHARED)
header :=
*(*reflect.SliceHeader)(unsafe.Pointer(&mem)
)
memory =
*(*[]uint32)(unsafe.Pointer(&header))

Our experience with Go: cons
1. Messy vendoring of 3rd party libraries
2. Quality of community libraries varies a lot
3. Some issues with Yocto Go layer at the beginning
○ all gone after recent efforts of integrating Go with Yocto
4. While using cgo all the easiness of cross-compiling is gone

Our experience with Go: pros
1. Easy transition from C/Python (took couple of days to be
productive in Go)
2. Very nice tooling and standard library
3. Some tasks exchange between backend and client teams
happened, but we’ve been able to share lot of tools (CI, code
coverage)
4. We can share some code between the client and the backend
5. Really productive language (especially when developing some kind
of network communication)
6. Forced coding standard so all the code looks the same and is easy
to read

Demo
● ThermoStat ™
○ https://github.com/mendersoftware/thermostat

Comparing C and Go

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