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Using linux environment variable in cgo failed #43364

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bill0119 opened this issue Dec 24, 2020 · 4 comments
Closed

Using linux environment variable in cgo failed #43364

bill0119 opened this issue Dec 24, 2020 · 4 comments
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@bill0119
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What version of Go are you using (go version)?

$ go version 1.15.6

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env

GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/home/bill/.cache/go-build"

GOENV="/home/bill/.config/go/env"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GOMODCACHE="/home/bill/go/pkg/mod"

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

GOPATH="/home/bill/go"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/usr/lib/go-1.15"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/usr/lib/go-1.15/pkg/tool/linux_amd64"

GCCGO="gccgo"

AR="ar"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD=""

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build550771112=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Using cgo to load a shared library in linux.

tree
.
├── inc
│   └── mylib.h
├── libmylib.so
├── main.go
├── mylib.o
└── src
    └── mylib.c

src/mylib.c

#include 

void PrintHello()
{
    printf("Hello\n");
}

inc/mylib.h

void PrintHello();

main.go

package main

/*
#cgo linux CFLAGS: -I${LIB_PATH}/inc
#cgo linux LDFLAGS: -lmylib
#cgo linux LDFLAGS: -L${LIB_PATH}/cgo
#include "mylib.h"
*/
import "C"

func main() {
        C.PrintHello()
}

Compile shared library

gcc -fPIC -c src/mylib.c
gcc -shared mylib.o -o libmylib.so

Set the env.

export LIB_PATH=/home/bill/project/cgo
export LD_LIBRARY_PATH=/home/bill/project/cgo

run the code

go run main.go
/home/bill/project/cgo/main.go: malformed #cgo argument: -I${LIB_PATH}/inc

What did you expect to see?

No environment var is ok

package main

/*
#cgo linux CFLAGS: -I/home/bill/project/cgo/inc
#cgo linux LDFLAGS: -lmylib
#cgo linux LDFLAGS: -L/home/bill/project/cgo
#include "mylib.h"
*/
import "C"

func main() {
        C.PrintHello()
}

go run main.go
Hello
@mengzhuo
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  1. Just remove ${LIB_PATH} in cgo arguments and put all files in the package.

  2. You might want to check "C_INCLUDE_PATH" and setting
    https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
    and use Makefile to overwrite these enviorment values.

@bill0119
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bill0119 commented Dec 24, 2020 •
edited

  1. Just remove ${LIB_PATH} in cgo arguments and put all files in the package.
  2. You might want to check "C_INCLUDE_PATH" and setting
    https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
    and use Makefile to overwrite these enviorment values.

So I can't load library in different folder? It seems not convenient.

@mengzhuo
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  1. Just remove ${LIB_PATH} in cgo arguments and put all files in the package.
  2. You might want to check "C_INCLUDE_PATH" and setting
    https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
    and use Makefile to overwrite these enviorment values.

So I can't load library in different folder? It seems not convenient.

That's what I mean in "2", for example: export C_INCLUDE_PATH=$C_INCLUDE_PATH:/your-custom-include-path

@bill0119
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  1. Just remove ${LIB_PATH} in cgo arguments and put all files in the package.
  2. You might want to check "C_INCLUDE_PATH" and setting
    https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
    and use Makefile to overwrite these enviorment values.

So I can't load library in different folder? It seems not convenient.

That's what I mean in "2", for example: export C_INCLUDE_PATH=$C_INCLUDE_PATH:/your-custom-include-path

https://golang.org/cmd/cgo/#hdr-Using_cgo_with_the_go_command

only ${SRCDIR} can be accept?
When the cgo directives are parsed, any occurrence of the string ${SRCDIR} will be replaced by the absolute path to the directory containing the source file. This allows pre-compiled static libraries to be included in the package directory and linked properly. For example if package foo is in the directory /go/src/foo:

// #cgo LDFLAGS: -L${SRCDIR}/libs -lfoo

@bill0119 bill0119 reopened this Dec 24, 2020
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@mengzhuo @gopherbot @bill0119