1. gccgo和go tools

gotools目录是编译go tools的. 到时候要自己改build源码, 自己生成tools?

go的代码在libgo

https://github.com/golang/go/wiki/GccgoCrossCompilation#build-a-cross-gccgo-aware-version-of-the-go-tool

https://github.com/golang/go/wiki/GccgoCrossCompilation

https://github.com/karalabe/xgo

2. 使用go tools和gccgo

https://medium.com/@chrischdi/cross-compiling-go-for-raspberry-pi-dc09892dc745

3. crosstool ng(我最后用的是这个)

https://crosstool-ng.github.io/docs/configuration/

crosstool-ng可以打印shell的调用栈, 比如:

[INFO ]  Retrieving needed toolchain components' tarballs
[EXTRA]    Retrieving 'automake-1.16.1'
[EXTRA]    Verifying SHA512 checksum for 'automake-1.16.1.tar.xz'
[EXTRA]    Retrieving 'linux-4.9.156'
[ERROR]    linux: download failed
[ERROR]   
[ERROR]  >>
[ERROR]  >>  Build failed in step 'Retrieving needed toolchain components' tarballs'
[ERROR]  >>        called in step '(top-level)'
[ERROR]  >>
[ERROR]  >>  Error happened in: CT_Abort[scripts/functions@487]
[ERROR]  >>        called from: CT_DoFetch[scripts/functions@2103]
[ERROR]  >>        called from: CT_PackageRun[scripts/functions@2063]
[ERROR]  >>        called from: CT_Fetch[scripts/functions@2174]
[ERROR]  >>        called from: do_kernel_get[scripts/build/kernel/linux.sh@22]
[ERROR]  >>        called from: main[scripts/crosstool-NG.sh@647]
[ERROR]  >>

是因为使用了trap ... ERR技术.
在crosstool-ng-1.24.0/scripts/functions中, trap CT_OnError ERR, 具体见CT_OnError函数.

# Install the fault handler
trap CT_OnError ERR
# Inherit the fault handler in subshells and functions
set -E
# Make pipes fail on the _first_ failed command
# Not supported on bash < 3.x, but we need it, so drop the obsolete bash-2.x
set -o pipefail

help trap和help set说的很清楚

上面这个CT_OnError函数用了下面的思路: bash默认有变量FUNCNAME BASH_SOURCE BASH_LINENO, 这些是数组, 保存了调用栈. https://unix.stackexchange.com/questions/462156/how-do-i-find-the-line-number-in-bash-when-an-error-occured

4. 编译gcc的理论基础

https://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/

https://solarianprogrammer.com/2018/05/06/building-gcc-cross-compiler-raspberry-pi/

5. 编译过程for x86_64

5.1. 下载gcc9.2源码, release版本就可以

axel http://www.netgull.com/gcc/releases/gcc-9.2.0/gcc-9.2.0.tar.xz

5.2. 安装依赖

apt install build-essential libgmp-dev libmpfr-dev libmpc-dev

5.3. 解压gcc 编译

cd gcc-9.2.0

mkdir objdir && cd objdir

../configure --prefix=/home/byj/repo/gorepo/gcc --enable-languages=go --disable-multilib

# 虽然没有写明要c和c++, 但默认是肯定有的
make -j

5.4. 编译完成后

make install

5.5. 会在指定目录下生成

gcc c++ g++ 

go gofmt gccgo

5.6. 使用

export LD_LIBRARY_PATH=~/repo/gorepo/gcc/lib64

PATH=~/repo/gorepo/gcc/bin:$PATH

go build hello.go

会生成hello可执行文件, 默认动态链接, 大小70K

动态库libgo.so大小48M, strip后26M

压缩后5M

$ ldd hello
    linux-vdso.so.1 =>  (0x00007ffe35580000)
    libgo.so.14 => /home/byj/repo/gorepo/gcc/lib64/libgo.so.14 (0x00007f5fae036000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f5fadd05000)
    libgcc_s.so.1 => /home/byj/repo/gorepo/gcc/lib64/libgcc_s.so.1 (0x00007f5fadaee000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5fad723000)
    /lib64/ld-linux-x86-64.so.2 (0x000055cdd4f10000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f5fad506000)

5.7. 交叉编译情况下不会编译gotools

gcc的住Makefile.in文件中, 搜索gotools

configure-host:
    ...
    maybe-configure-gotools
    ...

configure-target:
    没有maybe-configure-gotools

gotools包括

gcc/gotools/Makefile.am中也写了

if NATIVE

编译gccgo