Dump Compiler Options

Inspect and dump mainstream compilers(gcc/clang/msvc) predefined macros, c/c++ language standard and search paths.

Predefined macros

Pre-defined C/C++ Compiler Macros

Guide to predefined macros in C++ compilers (gcc, clang, msvc etc.)

gnu/gcc

Predefined Macros (The C Preprocessor)

• Standard Predefined Macros
• Common Predefined Macros

Invocation (The C Preprocessor): You can invoke the preprocessor either with the cpp command, or via gcc -E.

GCC Preprocessor Options

-dletters: Says to make debugging dumps during compilation as specified by letters.

-dM
Instead of the normal output, generate a list of ‘#define’ directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file foo.h, the command

touch foo.h; cpp -dM foo.h

shows all the predefined macros.

g++ - GCC dump preprocessor defines - Stack Overflow

echo 空流预编译：

# echo | cpp -dM
# echo | gcc -E -dM -
# echo | g++ -E -dM -
$ echo | gcc -x c -E -dM -
$ echo | g++ -x c++ -E -dM -

或指定空文件 /dev/null 预编译：

# cpp -dM - < /dev/null
# gcc -E -dM - < /dev/null
$ gcc -x c -E -dM - < /dev/null
$ gcc -x c++ -E -dM - < /dev/null
# or
$ gcc -x c -E -dM /dev/null
$ gcc -x c++ -E -dM /dev/null

包含特定头文件：

$ echo "#include <stdio.h>" | cpp -dM
# cpp -dM -include sys/socket.h < /dev/null
$ gcc -E -dM -include sys/socket.h - < /dev/null

指定C++版本：

$ echo | gcc -x c++ -E -dM -std=c++11 -
$ gcc -x c++ -E -dM -std=c++11 /dev/null

clang/llvm

Clang Preprocessor options

• Dumping preprocessor state

在 macOS 上，gcc/g++ 是 XcodeDefault.xctoolchain 下 clang/clang++ 的 shims or wrapper executables。

clang 兼容 gcc 大部分常规命令，可替代 gcc 执行 -E -dM 预处理命令，输出预定义宏。

clang 还可通过 -target / -arch 选项指定 Cross-Compilation 的目标 CPU 架构，输出对应 CPU 下的一些预定义宏。

clang -print-targets 和 objdump --version 输出 Registered Targets。
clang --print-supported-cpus 列出指定 target 支持的处理器。

IA32（_ILP32）/IA64（_LP64）：

$ clang -x c -E -dM -arch i386 /dev/null
$ clang -x c -E -dM -arch x86_64 /dev/null

ARM32（_ILP32）/ARM64（_LP64）：

$ clang -x c -E -dM -arch armv7s /dev/null
$ clang -x c -E -dM -arch arm64 /dev/null

可以通过管道导给 grep 过滤不同 CPU 架构下 __SIZEOF_INT__，__SIZEOF_LONG__，__SIZEOF_POINTER__，__BYTE_ORDER__，__BIGGEST_ALIGNMENT__ 等预定义宏。

msvc

Preprocessor
Predefined macros
/P (Preprocess to a File)

Preprocesses C and C++ source files and writes the preprocessed output to a file.

The following command line preprocesses ADD.C, preserves comments, adds #line directives, and writes the result to a file, ADD.I:

CL /P /C ADD.C

Provide the ability to list predefined macros and their values like gcc and Clang do with their '-E -dM' options - Developer Community

c++ - How to find out cl.exe's built-in macros - Stack Overflow

/P preprocessor flag will emit the currently active macros based on the project build settings. I am not sure if it is exactly the equivalent of gcc command you have shown. The output is in .I file.

echo // > foo.cpp; cl /Zc:preprocessor /PD foo.cpp

# For C
echo // > foo.cpp; cl /nologo /Zc:preprocessor /PD /EHs /TC foo.cpp | sort; rm foo.cpp, foo.obj

# For C++
echo // > foo.cpp; cl /nologo /Zc:preprocessor /PD /EHs /TP foo.cpp | sort; rm foo.cpp, foo.obj

c/c++ standard

g++ - How can I find the default version of the c++ language standard used by my compiler and change it? - Stack Overflow

gnu/gcc

gcc - How can I tell what standard my C is in? - Software Engineering Stack Exchange

Language Standards Supported by GCC

2.1 C Language: The default, if no C language dialect options are given, is -std=gnu17.
2.2 C++ Language: The default, if no C++ language dialect options are given, is -std=gnu++17.

gcc -std=c++ @rpi4b-ubuntu

$ gcc --version
gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ man gcc | grep -e "-std=c++"
           -std=c++98.
               GNU dialect of -std=c++98.
               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.
               GNU dialect of -std=c++14.  The name gnu++1y is deprecated.
               GNU dialect of -std=c++17.  This is the default for C++ code.  The name gnu++1z
               GNU dialect of -std=c++20.  Support is experimental, and could change in
               GNU dialect of -std=c++2b.  Support is highly experimental, and will almost
           This flag is enabled by default for -std=c++17.

$ man g++ | grep "This is the default for C++ code"
               GNU dialect of -std=c++17.  This is the default for C++ code.  The name gnu++1z

Which C++ standard is the default when compiling with g++? - Stack Overflow

You can also check with gdb:

1. $ g++ -g hello.cpp : Compile program with -g flag to generate debug info
2. $ gdb a.out : Debug program with gdb
3. (gdb) b main : Put a breakpoint at main
4. (gdb) r : Run program (will pause at breakpoint)
5. (gdb) info source - lldb 没有 info 命令

Prints out something like:

gdb info source @rpi4b-ubuntu

(gdb) info source
Current source file is hello.cpp
Compilation directory is /home/pifan/Projects/cpp
Located in /home/pifan/Projects/cpp/hello.cpp
Contains 7 lines.
Source language is c++.
Producer is GNU C++17 11.4.0 -mlittle-endian -mabi=lp64 -g -fasynchronous-unwind-tables -fstack-protector-strong -fstack-clash-protection.
Compiled with DWARF 5 debugging format.
Does not include preprocessor macro info.
(gdb) exit

What is the default C -std standard version for the current GCC (especially on Ubuntu)? - Stack Overflow

rpi4b-ubuntu

$ gcc -x c -E -dM /dev/null | grep -F __STDC_VERSION__
#define __STDC_VERSION__ 201710L

$ g++ -x c++ -E -dM /dev/null | grep -F __cplusplus
#define __cplusplus 201703L

If you feel like finding it out empirically without reading any manuals.

• Standard Predefined Macros 中有关于 __STDC_VERSION__ 和 __cplusplus 的说明。
• Common Predefined Macros 有关于宏 __STRICT_ANSI__ 的说明。

stdc.cstdc.sh

#include <stdio.h>

int main(void) {
#ifdef __STDC_VERSION__
    printf("__STDC_VERSION__ = %ld \n", __STDC_VERSION__);
#endif
#ifdef __STRICT_ANSI__
    puts("__STRICT_ANSI__");
#endif
    return 0;
}

#!/usr/bin/env bash

uname -a
echo
gcc --version
echo

oname=stdc-`arch`.out
for std in c89 c99 c11 c17 gnu89 gnu99 gnu11 gnu17; do
  echo $std
  gcc stdc.c -std=$std -o $oname && ./$oname
  echo
done
echo default
gcc stdc.c -o $oname && ./$oname

rpi4b-ubuntu 下输出结果如下：

STDC_VERSION & STRICT_ANSI

./stdc.sh
Linux rpi4b-ubuntu 5.15.0-1053-raspi #56-Ubuntu SMP PREEMPT Mon Apr 15 18:50:10 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


c89
__STRICT_ANSI__

c99
__STDC_VERSION__ = 199901
__STRICT_ANSI__

c11
__STDC_VERSION__ = 201112
__STRICT_ANSI__

c17
__STDC_VERSION__ = 201710
__STRICT_ANSI__

gnu89

gnu99
__STDC_VERSION__ = 199901

gnu11
__STDC_VERSION__ = 201112

gnu17

stdcpp.cppstdcpp.sh

#include <iostream>

int main(void) {
#ifdef __cplusplus
    std::cout << __cplusplus << std::endl;
#endif
#ifdef __STRICT_ANSI__
    std::cout << "__STRICT_ANSI__" << std::endl;
#endif
    return 0;
}

#!/usr/bin/env bash

uname -a
echo
g++ --version
echo

oname=stdcpp-`arch`.out
for std in c++98 c++11 c++14 c++17 gnu++98 gnu++11 gnu++14 gnu++17; do
  echo $std
  g++ stdcpp.cpp -std=$std -o $oname && ./$oname
  echo
done
echo default
g++ stdcpp.cpp -o $oname && ./$oname

rpi4b-ubuntu 下输出结果如下：

cplusplus & __STRICT_ANSI

./stdcpp.sh
Linux rpi4b-ubuntu 5.15.0-1053-raspi #56-Ubuntu SMP PREEMPT Mon Apr 15 18:50:10 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


c++98
199711
__STRICT_ANSI__

c++11
201103
__STRICT_ANSI__

c++14
201402
__STRICT_ANSI__

c++17
201703
__STRICT_ANSI__

gnu++98
199711

gnu++11
201103

gnu++14
201402

gnu++17
201703

default
201703

clang/llvm

C Language Features

If no -std option is specified, clang defaults to gnu17 mode.

Clang - C++ Programming Language Status

C++17 implementation status:

Clang 5 and later implement all the features of the ISO C++ 2017 standard.
By default, Clang 16 or later builds C++ code according to the C++17 standard.

clang default @mbpa2991/macOS_Sonoma

$ man clang | grep -F default
              The default C language standard is gnu17, except on PS4, where
              The default C++ language standard is gnu++98.

libc++ woes with Xcode 14 | Apple Developer Forums

What is the default C -std standard version for the current GCC (especially on Ubuntu)? - Stack Overflow

macOS clang/gcc

gcc -E -dM -x c /dev/null | grep -F __STDC_VERSION__
#define __STDC_VERSION__ 201710L

g++ -E -dM -x c++ /dev/null | grep -F __cplusplus
#define __cplusplus 199711L

mbpa2991/macOS_Sonoma 下执行 ./stdc.sh 输出：

STDC_VERSION & STRICT_ANSI

$ ./stdc.sh
Darwin mbpa2991.local 23.5.0 Darwin Kernel Version 23.5.0: Sat Apr 13 17:29:54 PDT 2024; root:xnu-10063.120.104~34/RELEASE_ARM64_T6031 arm64

Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: arm64-apple-darwin23.5.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

c89
__STRICT_ANSI__

c99
__STDC_VERSION__ = 199901
__STRICT_ANSI__

c11
__STDC_VERSION__ = 201112
__STRICT_ANSI__

c17
__STDC_VERSION__ = 201710
__STRICT_ANSI__

gnu89

gnu99
__STDC_VERSION__ = 199901

gnu11
__STDC_VERSION__ = 201112

gnu17
__STDC_VERSION__ = 201710

default
__STDC_VERSION__ = 201710

mbpa2991/macOS_Sonoma 下执行 ./stdcpp.sh 输出：

cplusplus & __STRICT_ANSI

$ ./stdcpp.sh
Darwin mbpa2991.local 23.5.0 Darwin Kernel Version 23.5.0: Sat Apr 13 17:29:54 PDT 2024; root:xnu-10063.120.104~34/RELEASE_ARM64_T6031 arm64

Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: arm64-apple-darwin23.5.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

c++98
199711
__STRICT_ANSI__

c++11
201103
__STRICT_ANSI__

c++14
201402
__STRICT_ANSI__

c++17
201703
__STRICT_ANSI__

gnu++98
199711

gnu++11
201103

gnu++14
201402

gnu++17
201703

default
199711

_LIBCPP_VERSION

⚙ D134187 [libc++] Document the format of _LIBCPP_VERSION

• llvm-project/libcxx/include/__config

_LIBCPP_VERSION represents the version of libc++, which matches the version of LLVM.
Given a LLVM release LLVM XX.Y.ZZ (e.g. LLVM 16.0.1 == 16.0.01), _LIBCPP_VERSION is defined to XXYZZ.

⚙ D26062 Alternative solution for detecting libc++'s version.

XCode now defaults to C++20 : r/cpp

执行 grep 搜索 _LIBCPP_VERSION 的定义：

grep -R -H "#define _LIBCPP_VERSION" --include=__config --exclude-dir=System / 2>/dev/null

_LIBCPP_VERSION

$ cmdpath=/Library/Developer/CommandLineTools
$ grep -R -H "#define _LIBCPP_VERSION" $cmdpath 2>/dev/null

/Library/Developer/CommandLineTools/usr/include/c++/v1/__config:#define _LIBCPP_VERSION 11000
/Library/Developer/CommandLineTools/usr/include/c++/v1/version:#define _LIBCPP_VERSIONH
/Library/Developer/CommandLineTools/usr/include/c++/v1/__cxx_version:#define _LIBCPP_VERSIONH

/Library/Developer/CommandLineTools/SDKs/MacOSX11.3.sdk/usr/include/c++/v1/__config:#define _LIBCPP_VERSION 12000
/Library/Developer/CommandLineTools/SDKs/MacOSX11.3.sdk/usr/include/c++/v1/version:#define _LIBCPP_VERSIONH
/Library/Developer/CommandLineTools/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/version:#define _LIBCPP_VERSIONH
/Library/Developer/CommandLineTools/SDKs/MacOSX14.4.sdk/usr/include/c++/v1/version:#define _LIBCPP_VERSIONH

$ xcdevpath=`xcode-select -p`
$ grep -R -H "#define _LIBCPP_VERSION" $xcdevpath 2>/dev/null

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/c++/v1/version:#define _LIBCPP_VERSIONH
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/version:#define _LIBCPP_VERSIONH

c++ - How to detect the libstdc++ version in Clang? - Stack Overflow

libcpp_version.cpp

#include <iostream>
#include <string>

using namespace std;

int main(int argc, const char * argv[])
{
    cout<<"_LIBCPP_VERSION = "<<_LIBCPP_VERSION<<endl;
    return 0;
}

clang 15.0.0 下输出 _LIBCPP_VERSION = 170006。

# c++/g++/clang++
$ clang++ libcpp_version.cpp -o libcpp_version && ./libcpp_version
_LIBCPP_VERSION = 170006

msvc

Predefined macros

_MSVC_LANG Defined as an integer literal that specifies the C++ language standard targeted by the compiler. It's set only in code compiled as C++. The macro is the integer literal value 201402L by default, or when the /std:c++14 compiler option is specified. .

/std (Specify Language Standard Version)

C standards support: You can invoke the Microsoft C compiler by using the /TC or /Tc compiler option. It's used by default for code that has a .c file extension, unless overridden by a /TP or /Tp option. The default C compiler (that is, the compiler when /std:c11 or /std:c17 isn't specified) implements ANSI C89, but includes several Microsoft extensions, some of which are part of ISO C99.

C++ standards support: The /std option in effect during a C++ compilation can be detected by use of the _MSVC_LANG preprocessor macro. For more information, see Preprocessor Macros.

Important

Because some existing code depends on the value of the macro __cplusplus being 199711L, the MSVC compiler doesn't change the value of this macro unless you explicitly opt in by setting /Zc:__cplusplus. Specify /Zc:__cplusplus and the /std option to set __cplusplus to the appropriate value.

Predefined macros: __cplusplus - cppreference.com

The /std:c++14 option enables C++14 standard-specific features implemented by the MSVC compiler. This option is the default for code compiled as C++. It's available starting in Visual Studio 2015 Update 3.

Search Paths

Header Search Paths

Preprocessor Options: -dI : Output ‘#include’ directives in addition to the result of preprocessing.

macOS cpp -dIrpi4b-ubuntu cpp -dI

$ echo | cpp -dI
# 1 "<stdin>"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 417 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "<stdin>" 2

# 查看导入 <stdio.h> 的依赖展开
$ echo "#include <stdio.h>" | cpp -dI

$ echo | cpp -dI
# 0 "<stdin>"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "<stdin>"

# 查看导入 <stdio.h> 的依赖展开
$ echo "#include <stdio.h>" | cpp -dI

运行 clang -v -x c -E /dev/null 或 clang -v -x c++ -E /dev/null 执行预处理，可以查看 C/C++ 语言的 Header Search Paths。

#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/include
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks (framework directory)
End of search list.

If you want to see your header include paths for libstdc++ and libc++, do this:

# GNU C++ runtime
$ echo | clang -x c++ -Wp,-v -stdlib=libstdc++ -fsyntax-only -

# LLVM C++ runtime
$ echo | clang -x c++ -Wp,-v -stdlib=libc++ -fsyntax-only -

涉及到两个选项：

1. Preprocessor Options - -Wp,option : to bypass the compiler driver and pass option directly through to the preprocessor.
2. Warning Options - -fsyntax-only : Check the code for syntax errors, but don't do anything beyond that.

macOS <stdio.h> / <iostream>rpi4b-ubuntu <stdio.h> / <iostream>

# gcc stdc.c -E -### : llvm-gcc 调用 clang -cc1 预处理
$ gcc stdc.c -E -v
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/stdio.h

# g++ stdcpp.cpp -E -### : llvm-g++ 也是调用 clang -cc1 预处理
$ g++ stdcpp.cpp -E -v
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream

# gcc stdc.c -E -### : 调用 /usr/lib/gcc/aarch64-linux-gnu/11/cc1 -E 预处理
$ gcc stdc.c -E -v

#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/aarch64-linux-gnu/11/include
 /usr/local/include
 /usr/include/aarch64-linux-gnu
 /usr/include
End of search list.

/usr/include/stdio.h

COMPILER_PATH=/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/:/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/:/usr/lib/gcc/aarch64-linux-gnu/11/../../../../lib/:/lib/aarch64-linux-gnu/:/lib/../lib/:/usr/lib/aarch64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/aarch64-linux-gnu/11/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-E' '-v' '-mlittle-endian' '-mabi=lp64'

# g++ stdcpp.cpp -E -### : 调用 /usr/lib/gcc/aarch64-linux-gnu/11/cc1plus -E 预处理
$ g++ stdcpp.cpp -E -v

/usr/include/c++/11/iostream

COMPILER_PATH=/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/:/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/aarch64-linux-gnu/11/:/usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/:/usr/lib/gcc/aarch64-linux-gnu/11/../../../../lib/:/lib/aarch64-linux-gnu/:/lib/../lib/:/usr/lib/aarch64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/aarch64-linux-gnu/11/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-E' '-v' '-shared-libgcc' '-mlittle-endian' '-mabi=lp64'

---

VC2015 的头文件 INCLUDE 路径为：

• C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include
• C:\Program Files (x86)\Windows Kits\10\Include\10.0.10150.0\ucrt

Library Search Paths

执行 clang -Xlinker -v 指定链接选项，不指定链接目标，则只显示 configured to support archs 信息：

• Options for Linking - -Xlinker option : Pass option as an option to the linker.

$ clang -Xlinker -v
@(#)PROGRAM:ld PROJECT:ld-1053.12
BUILD 15:45:29 Feb  3 2024
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
will use ld-classic for: armv6 armv7 armv7s arm64_32 i386 armv6m armv7k armv7m armv7em
LTO support using: LLVM version 15.0.0 (static support for 29, runtime is 29)
TAPI support using: Apple TAPI version 15.0.0 (tapi-1500.3.2.2)

也可执行 clang -print-targets 查看 Registered Targets，参考 How to list supported target architectures in clang?。

指定链接空文件 /dev/null，可以查看 Library/Framework search paths，直接报错：

clang -Xlinker -v @mbpa2991/macOS_Sonoma

$ clang -Xlinker -v /dev/null
@(#)PROGRAM:ld PROJECT:ld-1053.12
BUILD 15:45:29 Feb  3 2024
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
will use ld-classic for: armv6 armv7 armv7s arm64_32 i386 armv6m armv7k armv7m armv7em
LTO support using: LLVM version 15.0.0 (static support for 29, runtime is 29)
TAPI support using: Apple TAPI version 15.0.0 (tapi-1500.3.2.2)
Library search paths:
        /usr/local/lib
        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib
        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib/swift
Framework search paths:
        /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks
clang: error: unable to execute command: Segmentation fault: 11
clang: error: linker command failed due to signal (use -v to see invocation)

macOS 编译链接 C/C++

macOS 上编译链接 C 代码：dry-run: gcc stdc.c -###；compile: gcc stdc.c -o c.out -v。
macOS 上编译链接 C++ 代码：dry-run: g++ stdcpp.cpp -###；compile: g++ stdcpp.cpp -o cpp.out -v。

• gcc/g++ 都只调用了 clang cc1 和 ld 两步命令。
• gcc std.c 链接 libLTO.dylib、-lSystem 和 libclang_rt.osx.a；g++ stdcpp.cpp 在 -lSystem 前面插增链接选项 -lc++。
• 执行 otool -L c.out / otool -L cpp.out 可查看依赖的动态库（dylib）。

Ubuntu 下执行 gcc/g++ 命令，调用 collect2 和 ld 链接，最终报错：

gcc collect2 -lcg++ collect2 -lstdc++

$ gcc -Xlinker -v /dev/null
collect2 version 11.4.0
/usr/bin/ld -plugin /usr/lib/gcc/aarch64-linux-gnu/11/liblto_plugin.so -plugin-opt=/usr/lib/gcc/aarch64-linux-gnu/11/lto-wrapper -plugin-opt=-fresolution=/tmp/cc2Mlb39.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --build-id --eh-frame-hdr --hash-style=gnu --as-needed -dynamic-linker /lib/ld-linux-aarch64.so.1 -X -EL -maarch64linux --fix-cortex-a53-843419 -pie -z now -z relro /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/Scrt1.o /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/crti.o /usr/lib/gcc/aarch64-linux-gnu/11/crtbeginS.o -L/usr/lib/gcc/aarch64-linux-gnu/11 -L/usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu -L/usr/lib/gcc/aarch64-linux-gnu/11/../../../../lib -L/lib/aarch64-linux-gnu -L/lib/../lib -L/usr/lib/aarch64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/aarch64-linux-gnu/11/../../.. -v -lgcc --push-state --as-needed -lgcc_s --pop-state -lc -lgcc --push-state --as-needed -lgcc_s --pop-state /usr/lib/gcc/aarch64-linux-gnu/11/crtendS.o /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/crtn.o
GNU ld (GNU Binutils for Ubuntu) 2.38
/usr/bin/ld: /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/Scrt1.o: in function `_start':
(.text+0x1c): undefined reference to `main'
/usr/bin/ld: (.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

$ g++ -x c++ -Xlinker -v /dev/null
collect2 version 11.4.0
/usr/bin/ld -plugin /usr/lib/gcc/aarch64-linux-gnu/11/liblto_plugin.so -plugin-opt=/usr/lib/gcc/aarch64-linux-gnu/11/lto-wrapper -plugin-opt=-fresolution=/tmp/ccx8f9Ks.res -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --build-id --eh-frame-hdr --hash-style=gnu --as-needed -dynamic-linker /lib/ld-linux-aarch64.so.1 -X -EL -maarch64linux --fix-cortex-a53-843419 -pie -z now -z relro /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/Scrt1.o /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/crti.o /usr/lib/gcc/aarch64-linux-gnu/11/crtbeginS.o -L/usr/lib/gcc/aarch64-linux-gnu/11 -L/usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu -L/usr/lib/gcc/aarch64-linux-gnu/11/../../../../lib -L/lib/aarch64-linux-gnu -L/lib/../lib -L/usr/lib/aarch64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/aarch64-linux-gnu/11/../../.. -v /tmp/ccqgv1oL.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/aarch64-linux-gnu/11/crtendS.o /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/crtn.o
GNU ld (GNU Binutils for Ubuntu) 2.38
/usr/bin/ld: /usr/lib/gcc/aarch64-linux-gnu/11/../../../aarch64-linux-gnu/Scrt1.o: in function `_start':
(.text+0x1c): undefined reference to `main'
/usr/bin/ld: (.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

Ubuntu 编译链接 C/C++

ubuntu 上编译链接 C 代码：dry-run: gcc stdc.c -###；compile: gcc stdc.c -o c.out -v。

• gcc 依次调用 cc1->as->collect2，链接 Scrt1.o,crti.o,crtbeginS.o,-lc（[g]libc）,crtendS.o,crtn.o。

ubuntu 上编译链接 C++ 代码：dry-run: g++ stdcpp.cpp -###；compile: g++ stdcpp.cpp -o cpp.out -v。

• g++ 依次调用 cc1plus->as->collect2，链接 Scrt1.o,crti.o,crtbeginS.o,-lstdc++（libstdc++）,crtendS.o,crtn.o。

说明：

• gcc 的 cc1 已经集成了 cpp 预处理。
• collect2 内部调用 real ld 完成最终的链接工作。
• 关于 crt(C Runtime)，参考 crtbegin.o vs. crtbeginS.o，Mini FAQ about the misc libc/gcc crt files. 和 ELF Format Cheatsheet | Sections, Common objects and functions。

---

VC2015 的库文件 LIB 路径为：

• C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\lib
• C:\Program Files (x86)\Windows Kits\10\Lib\10.0.10150.0\ucrt\x86

Library Dependencies

执行 gcc/g++ 编译链接时，可指定 -### dry-run，查看完整编译链接流程：

• gcc stdc.c -###
• g++ stdcpp.cpp -###

ABI Policy and Guidelines - Checking Active

• elf - Determine direct shared object dependencies of a Linux binary? - Stack Overflow
• windows - Discovery of Dynamic library dependency on Mac OS & Linux - Stack Overflow
• How to find out the dynamic libraries executables loads when run? - Unix & Linux Stack Exchange

c++ - How do you find what version of libstdc++ library is installed on your linux machine? - Stack Overflow

ldd

ldd - print shared object dependencies.

ldd 打印依赖的动态共享库：libc.so.6, libstdc++.so.6。

ldd c.outldd cpp.out

rpi4b-ubuntu $ ldd c.out
    linux-vdso.so.1 (0x0000ffffa4f6c000)
    libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffffa4d70000)
    /lib/ld-linux-aarch64.so.1 (0x0000ffffa4f33000)

rpi4b-ubuntu $ ldd cpp.out
    linux-vdso.so.1 (0x0000ffff968c5000)
    libstdc++.so.6 => /lib/aarch64-linux-gnu/libstdc++.so.6 (0x0000ffff96640000)
    libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffff96490000)
    libm.so.6 => /lib/aarch64-linux-gnu/libm.so.6 (0x0000ffff963f0000)
    /lib/ld-linux-aarch64.so.1 (0x0000ffff9688c000)
    libgcc_s.so.1 => /lib/aarch64-linux-gnu/libgcc_s.so.1 (0x0000ffff963c0000)

---

macOS 与 Linux 上的 ldd 对应的命令是 otool -L：

mbpa2991 $ otool -L c.out
c.out:
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1345.100.2)

mbpa2991 $ otool -L cpp.out
cpp.out:
    /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1700.255.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1345.100.2)

但 /usr/lib 下并没有找到这两个 dylib，参考：

• Why are my system libraries and frameworks not visible in macOS Monterey?
• Missing librairies in /usr/lib on Big Sur?: Since Big Sur, it somehow all became virtual.

在 macOS 上的 Library search paths 中过滤 libSystem 和 libc++，只搜到了 libSystem.B.tbd 和 libc++.1.tbd 及一堆软链替身（如 libc.tbd、libc++.tbd）：

$ ls -l /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib | grep -E "lib(System|c\+\+)"
-rw-r--r--    1 root  wheel  309826 Nov 17  2021 libSystem.B.tbd
lrwxr-xr-x    1 root  wheel      15 Oct  7  2021 libSystem.tbd -> libSystem.B.tbd
-rw-r--r--    1 root  wheel  145622 Nov 13  2021 libc++.1.tbd
lrwxr-xr-x    1 root  wheel      12 Oct  7  2021 libc++.tbd -> libc++.1.tbd
-rw-r--r--    1 root  wheel   10571 Nov 13  2021 libc++abi.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libc.tbd -> libSystem.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libdl.tbd -> libSystem.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libgcc_s.1.tbd -> libSystem.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libm.tbd -> libSystem.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libpoll.tbd -> libSystem.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libproc.tbd -> libSystem.tbd
lrwxr-xr-x    1 root  wheel      13 Oct  7  2021 libpthread.tbd -> libSystem.tbd

查看 libSystem.B.tbd 可知，libSystem 不提供任何符号和代码，它链接了 /usr/lib/system 中的许多其他 dylib，并将它们的符号作为自己的符号重新导出（reexported-libraries）。

$ tree /usr/lib/system
/usr/lib/system
├── introspection
│   ├── libdispatch.dylib
│   └── libsystem_pthread.dylib
├── libsystem_kernel.dylib
├── libsystem_platform.dylib
├── libsystem_pthread.dylib
└── wordexp-helper

2 directories, 6 files

tdb vs. dylib

关于 tdb 和 dylib 的关系，参考：

• Why Xcode 7 shows *.tbd instead of *.dylib?
• macOS/iOS dylib、tbd 和 Framework 库详解

*.dylib is the compiled binary that contains the machine code.
TDB is the acronym for "Text Based Dylib stubs".
*.tbd is a smaller text file, similar to a cross-platform module map.

ldconfig

ldconfig - configure dynamic linker run-time bindings.

• -p / --print-cache: Print the lists of directories and candidate libraries stored in the current cache.

ldconfig -p 打印缓存中的动态共享库 libc.so.6, libstdc++.so.6。

ldconfig -p | grep libc.soldconfig -p | grep libstdc++

rpi4b-ubuntu $ ldconfig -p | grep libc.so
    libc.so.6 (libc6,AArch64, OS ABI: Linux 3.7.0) => /lib/aarch64-linux-gnu/libc.so.6

rpi4b-ubuntu $ ldconfig -p | grep libstdc++
    libstdc++.so.6 (libc6,AArch64) => /lib/aarch64-linux-gnu/libstdc++.so.6

objdump

-f

执行 file 命令查看 libc.so 文件属性（determine file type）：

$ file /lib/aarch64-linux-gnu/libc.so.6
/lib/aarch64-linux-gnu/libc.so.6: ELF 64-bit LSB shared object, ARM aarch64, version 1 (GNU/Linux), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, BuildID[sha1]=9e27cf97f03940293c6df3b107674ceda9c825d8, for GNU/Linux 3.7.0, stripped

执行 file 命令查看 libstdc++.so 文件属性：

$ file /lib/aarch64-linux-gnu/libstdc++.so.6
/lib/aarch64-linux-gnu/libstdc++.so.6: symbolic link to libstdc++.so.6.0.30

$ file /lib/aarch64-linux-gnu/libstdc++.so.6.0.30
/lib/aarch64-linux-gnu/libstdc++.so.6.0.30: ELF 64-bit LSB shared object, ARM aarch64, version 1 (GNU/Linux), dynamically linked, BuildID[sha1]=a012b2bb77110e84b266cd7425b50e57427abb02, stripped

objdump -a 查看 archive header；objdump -f 查看 file header。

• -a, --archive-headers Display archive header information
• -f, --file-headers Display the contents of the overall file header

objdump -f /lib/aarch64-linux-gnu/libc.so.6

/lib/aarch64-linux-gnu/libc.so.6:     file format elf64-littleaarch64
architecture: aarch64, flags 0x00000150:
HAS_SYMS, DYNAMIC, D_PAGED
start address 0x00000000000275e0

objdump -f /lib/aarch64-linux-gnu/libstdc++.so.6

/lib/aarch64-linux-gnu/libstdc++.so.6:     file format elf64-littleaarch64
architecture: aarch64, flags 0x00000150:
HAS_SYMS, DYNAMIC, D_PAGED
start address 0x0000000000000000

-x

objdump -x（--all-headers）: Display all available header information, including the symbol table and relocation entries.

1. Dynamic Section: 中的 NEEDED 为依赖的（动态）库：libc.so.6, libstdc++.so.6。
2. Version References: 中的 required 为依赖的（动态）库：GLIBC_2.17/GLIBC_2.34,GLIBCXX_3.4。
3. 依赖的符号后面也有 @GLIBC_2.17/@GLIBC_2.34,@GLIBCXX_3.4 标记。

objdump -x c.outobjdump -x cpp.out

rpi4b-ubuntu $ objdump -x c.out

Dynamic Section:
  NEEDED               libc.so.6

Version References:
  required from libc.so.6:
    0x06969197 0x00 03 GLIBC_2.17
    0x069691b4 0x00 02 GLIBC_2.34

SYMBOL TABLE:

0000000000000000       F *UND*  0000000000000000              __libc_start_main@GLIBC_2.34
0000000000000000       F *UND*  0000000000000000              printf@GLIBC_2.17

rpi4b-ubuntu $ objdump -x cpp.out

Dynamic Section:
  NEEDED               libstdc++.so.6
  NEEDED               libc.so.6

Version References:
  required from libc.so.6:
    0x069691b4 0x00 04 GLIBC_2.34
    0x06969197 0x00 03 GLIBC_2.17
  required from libstdc++.so.6:
    0x08922974 0x00 02 GLIBCXX_3.4

SYMBOL TABLE:

0000000000000000       O *UND*  0000000000000000              _ZSt4cout@GLIBCXX_3.4

readelf

readelf -h: Display the ELF file header.
readelf -l(--program-headers, --segments): Display the program headers
readelf -S(--section-headers, --sections): Display the sections' header
readelf -e(--headers): Equivalent to: -h -l -S
readelf -s(--syms): Display the symbol table.
readelf -d(--dynamic): Displays the contents of the file's dynamic section, if it has one.
readelf -a(--all): Displays the complete structure of an object file.

readelf -d c.outreadelf -d cpp.out

rpi4b-ubuntu $ readelf -d c.out

Dynamic section at offset 0xda0 contains 27 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

rpi4b-ubuntu $ readelf -d cpp.out

Dynamic section at offset 0xd60 contains 28 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

其中 NEEDED 标记表示依赖（动态）库：libc.so.6, libstdc++.so.6。

nm

nm - list symbols from object files.

依赖的符号后面也有 @GLIBC_2.17/@GLIBC_2.34,@GLIBCXX_3.4 标记。

nm c.outnm cpp.out

rpi4b-ubuntu $ nm c.out

0000000000000790 R _IO_stdin_used
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
                 U __libc_start_main@GLIBC_2.34
0000000000000754 T main
                 U printf@GLIBC_2.17

rpi4b-ubuntu $ nm cpp.out
0000000000000a10 t _Z41__static_initialization_and_destruction_0ii
                 U _ZNSolsEl@GLIBCXX_3.4
                 U _ZNSolsEPFRSoS_E@GLIBCXX_3.4
                 U _ZNSt8ios_base4InitC1Ev@GLIBCXX_3.4
                 U _ZNSt8ios_base4InitD1Ev@GLIBCXX_3.4
                 U _ZSt4cout@GLIBCXX_3.4
                 U _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GLIBCXX_3.4

man nm 查看 nm(1) - Linux manual page，其中有关于 symbol type 的详细说明。

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