Question

我正在尝试逐步构建以下示例代码：

#include <stdio.h>

int main(void) {
    puts("hello, world");
}

这是我的Makefile：

CC=clang
CFLAGS=-g
LD=ld
LDFLAGS=-macosx_version_min 10.12
LDLIBS=-L/usr/lib/system/

a.out: main.o
    $(LD) $(LDFLAGS) $< $(LOADLIBES) $(LDLIBS)

main.o: main.c
    $(CC) $(CFLAGS) $(CPPFLAGS) -c $<

创建main.o没有问题，但在链接阶段引发错误：

$ make
ld -macosx_version_min 10.12 main.o  -L/usr/lib/system/
Undefined symbols for architecture x86_64:
  "_puts", referenced from:
      _main in main.o
ld: symbol(s) not found for inferred architecture x86_64
make: *** [a.out] Error 1

ld似乎无法找到C标准库。我做错了什么？

供您参考，这是clang main.c -v的输出，它正确地进行链接：

$ clang main.c -v
Apple LLVM version 8.1.0 (clang-802.0.42)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
 "/Library/Developer/CommandLineTools/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.12.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu penryn -target-linker-version 278.4 -v -dwarf-column-info -debugger-tuning=lldb -resource-dir /Library/Developer/CommandLineTools/usr/bin/../lib/clang/8.1.0 -fdebug-compilation-dir /Users/sunqingyao/Projects/play-ground -ferror-limit 19 -fmessage-length 167 -stack-protector 1 -fblocks -fobjc-runtime=macosx-10.12.0 -fencode-extended-block-signature -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/x0/lrg8j6r535n4lvnfnj6lr2fr0000gn/T/main-f5cd6b.o -x c main.c
clang -cc1 version 8.1.0 (clang-802.0.42) default target x86_64-apple-darwin16.7.0
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Library/Developer/CommandLineTools/usr/bin/../lib/clang/8.1.0/include
 /Library/Developer/CommandLineTools/usr/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
 "/Library/Developer/CommandLineTools/usr/bin/ld" -demangle -lto_library /Library/Developer/CommandLineTools/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.12.0 -o a.out /var/folders/x0/lrg8j6r535n4lvnfnj6lr2fr0000gn/T/main-f5cd6b.o -lSystem /Library/Developer/CommandLineTools/usr/bin/../lib/clang/8.1.0/lib/darwin/libclang_rt.osx.a

我尝试将最后一行复制到Makefile，只是为了得到file not found错误：

$ make
/Library/Developer/CommandLineTools/usr/bin/ld -macosx_version_min 10.12 main.o  -demangle -lto_library /Library/Developer/CommandLineTools/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.12.0 -o a.out /var/folders/x0/lrg8j6r535n4lvnfnj6lr2fr0000gn/T/main-f5cd6b.o -lSystem /Library/Developer/CommandLineTools/usr/bin/../lib/clang/8.1.0/lib/darwin/libclang_rt.osx.a
ld: file not found: /var/folders/x0/lrg8j6r535n4lvnfnj6lr2fr0000gn/T/main-f5cd6b.o
make: *** [a.out] Error 1

Answer 1

如今，使用ld直接链接二进制文件是不寻常的，在macOS下，您需要添加-lc以强制它包含标准C库。

通常，使用cc来调用链接器会更好，并且它会安排传递正确的标记。

这个Makefile适合我：

CC=clang
CFLAGS=-g -mmacosx-version-min=10.12

main: main.o
    $(CC) -o main $(CFLAGS) $(LDFLAGS) main.o

无法链接到macOS上的C标准库

1 个答案: