Merge pull request #20 from devlights/add-cflags-ldflags

20.C_CFLAGS_LDFLAGS/README.md

@@ -0,0 +1,54 @@
+# これは何？
+
+CGOヘッダーには、C言語で利用する ```CFLAGS```, ```LDFLAGS``` が利用できます。
+
+外部ライブラリを利用する際は、CGOヘッダーにて指定します。
+
+```go
+/*
+#cgo CFLAGS: -I../lib
+#cgo LDFLAGS: -L../lib -lmylib
+
+#include <stdlib.h>
+#include "lib.c"
+*/
+import "C"
+```
+
+本サンプルを実行すると以下のようになります。
+
+```sh
+$ task
+task: [build-lib] make build
+gcc -g -O0 -Wall -Wextra -std=c17 -c /workspace/try-golang-cgo/20.C_CFLAGS_LDFLAGS/lib/lib.c -o /workspace/try-golang-cgo/20.C_CFLAGS_LDFLAGS/lib/lib.o 
+gcc -g -O0 -Wall -Wextra -std=c17 -fPIC -shared  -o ./libmylib.so /workspace/try-golang-cgo/20.C_CFLAGS_LDFLAGS/lib/lib.o 
+task: [build-capp] make build
+gcc -g -O0 -Wall -Wextra -std=c17 -c /workspace/try-golang-cgo/20.C_CFLAGS_LDFLAGS/capp/main.c -o /workspace/try-golang-cgo/20.C_CFLAGS_LDFLAGS/capp/main.o -I../lib
+gcc -g -O0 -Wall -Wextra -std=c17 -L../lib -o ./cApp /workspace/try-golang-cgo/20.C_CFLAGS_LDFLAGS/capp/main.o -lmylib
+task: [build-goapp] go build -o goApp
+task: [run-capp] LD_LIBRARY_PATH=../lib ./cApp
+[C ] hello world
+task: [run-goapp] ./goApp
+[C ] hello world
+task: [list-symbols] nm --extern-only capp/cApp   | grep -E ' [T|U] (main|myPrint)'
+0000000000001149 T main
+                 U myPrint
+task: [list-symbols] nm --extern-only goapp/goApp | grep -E ' [T|U] (main|myPrint)'
+000000000045c600 T main
+0000000000461030 T myPrint
+task: [ldd] LD_LIBRARY_PATH=lib ldd capp/cApp
+        linux-vdso.so.1 (0x00007ffe22799000)
+        libmylib.so => lib/libmylib.so (0x00007f29c42ce000)
+        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f29c409e000)
+        /lib64/ld-linux-x86-64.so.2 (0x00007f29c42da000)
+task: [ldd] ldd goapp/goApp
+        linux-vdso.so.1 (0x00007ffcd01a7000)
+        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fcf8ac0d000)
+        /lib64/ld-linux-x86-64.so.2 (0x00007fcf8ae3f000)
+```
+
+よく見ると、C言語のアプリの方は nm, ldd の結果ともに外部ライブラリの参照となっているが
+
+cgoの方は、soファイルが取り込まれているのか nm コマンドにて myPrint 関数が ```T``` で表示される。(C言語側は ```U```)
+
+また、ldd で見た場合に、```libmylib.so``` が出てこない。

20.C_CFLAGS_LDFLAGS/Taskfile.yml

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+# https://taskfile.dev
+
+version: '3'
+
+tasks:
+  default:
+    cmds:
+      - task: build-lib
+      - task: build-capp
+      - task: build-goapp
+      - task: run-capp
+      - task: run-goapp
+      - task: list-symbols
+      - task: ldd
+  clean:
+    cmds:
+      - make -C lib clean
+      - make -C capp clean
+      - rm -f goapp/goApp
+  build-lib:
+    dir: lib
+    cmds:
+      - make build
+  build-capp:
+    dir: capp
+    cmds:
+      - make build
+  build-goapp:
+    dir: goapp
+    cmds:
+      - go build -o goApp
+  run-capp:
+    dir: capp
+    cmds:
+      - LD_LIBRARY_PATH=../lib ./cApp
+  run-goapp:
+    dir: goapp
+    cmds:
+      - ./goApp
+  list-symbols:
+    cmds:
+      - nm --extern-only capp/cApp   | grep -E ' [T|U] (main|myPrint)'
+      - nm --extern-only goapp/goApp | grep -E ' [T|U] (main|myPrint)'
+  ldd:
+    cmds:
+      - LD_LIBRARY_PATH=lib ldd capp/cApp
+      - ldd goapp/goApp

20.C_CFLAGS_LDFLAGS/capp/.gitignore

@@ -0,0 +1,2 @@
+cApp
+*.o

20.C_CFLAGS_LDFLAGS/capp/Makefile

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+DESTDIR = .
+PROGRAM = cApp
+SRCS    = $(shell find $(PWD) -name "*.c" -type f)
+OBJS    = $(SRCS:%.c=%.o)
+CC      = gcc
+INCDIRS = -I../lib
+CFLAGS  = -g -O0 -Wall -Wextra -std=c17
+LDFLAGS = -L../lib
+LDLIBS  = -lmylib
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@ $(INCDIRS)
+
+$(PROGRAM): $(OBJS)
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $(DESTDIR)/$(PROGRAM) $(OBJS) $(LDLIBS)
+
+.PHONY: build
+build: $(PROGRAM)
+
+.PHONY: clean
+clean:
+	$(RM) $(OBJS) $(DESTDIR)/$(PROGRAM)

20.C_CFLAGS_LDFLAGS/capp/main.c

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+#include "lib.h"
+
+int main() {
+    myPrint("hello world");
+}

20.C_CFLAGS_LDFLAGS/goapp/.gitignore

@@ -0,0 +1 @@
+goApp

20.C_CFLAGS_LDFLAGS/goapp/main.go

@@ -0,0 +1,21 @@
+package main
+
+/*
+#cgo CFLAGS: -I../lib
+#cgo LDFLAGS: -L../lib -lmylib
+
+#include <stdlib.h>
+#include "lib.c"
+*/
+import "C"
+import "unsafe"
+
+func main() {
+	var (
+		goStr = "hello world"
+		cStr  = C.CString(goStr)
+	)
+	defer C.free(unsafe.Pointer(cStr))
+
+	C.myPrint(cStr)
+}

20.C_CFLAGS_LDFLAGS/lib/.gitignore

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+*.o

20.C_CFLAGS_LDFLAGS/lib/Makefile

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+DESTDIR = .
+PROGRAM = libmylib.so
+SRCS    = $(shell find $(PWD) -name "*.c" -type f)
+OBJS    = $(SRCS:%.c=%.o)
+CC      = gcc
+INCDIRS = 
+CFLAGS  = -g -O0 -Wall -Wextra -std=c17
+LDFLAGS =
+LDLIBS  =
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@ $(INCDIRS)
+
+$(PROGRAM): $(OBJS)
+	$(CC) $(CFLAGS) -fPIC -shared $(LDFLAGS) -o $(DESTDIR)/$(PROGRAM) $(OBJS) $(LDLIBS)
+
+.PHONY: build
+build: $(PROGRAM)
+
+.PHONY: clean
+clean:
+	$(RM) $(OBJS) $(DESTDIR)/$(PROGRAM)

20.C_CFLAGS_LDFLAGS/lib/lib.c

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+#include <stdio.h>
+
+void myPrint(const char *msg) {
+    printf("[C ] %s\n", msg);
+}

20.C_CFLAGS_LDFLAGS/lib/lib.h

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+#ifndef __LIB_H
+#define __LIB_H
+
+extern void myPrint(const char *msg);
+
+#endif /* __LIB_H */