GCC --verbose选项， -lpthread 和-pthread的区别

verbose的意思是冗长的，繁杂的。顾名思义，gcc --verbose 的意思就是打印出编译连接时的详细信息。

参考stackoverflow中的文章结合自己机器的信息给出分析（其实也就是翻译了一下。。嘿嘿。  原址：http://stackoverflow.com/questions/13440549/gcc-verbose-mode-output-explanation）

首先给出整体信息：

lysuns@ubuntu:~/APUE3/Chapter11$ gcc printids.c ../error/error.o  -pthread -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.8/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.8.2-19ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-i386/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-i386 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-i386 --with-arch-directory=i386 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-targets=all --enable-multiarch --disable-werror --with-arch-32=i686 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.8. (Ubuntu 4.8.-19ubuntu1)
COLLECT_GCC_OPTIONS='-pthread' '-v' '-mtune=generic' '-march=i686'
 /usr/lib/gcc/i686-linux-gnu/4.8/cc1 -quiet -v -imultiarch i386-linux-gnu -D_REENTRANT printids.c -quiet -dumpbase printids.c -mtune=generic -march=i686 -auxbase printids -version -fstack-protector -Wformat -Wformat-security -o /tmp/ccH2Lot0.s
GNU C (Ubuntu 4.8.-19ubuntu1) version 4.8. (i686-linux-gnu)
    compiled by GNU C version 4.8., GMP version 5.1., MPFR version 3.1.-p3, MPC version 1.0.
GGC heuristics: --param ggc-min-expand= --param ggc-min-heapsize=
ignoring nonexistent directory "/usr/local/include/i386-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/i686-linux-gnu/4.8/../../../../i686-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/i686-linux-gnu/4.8/include
 /usr/local/include
 /usr/lib/gcc/i686-linux-gnu/4.8/include-fixed
 /usr/include/i386-linux-gnu
 /usr/include
End of search list.
GNU C (Ubuntu 4.8.-19ubuntu1) version 4.8. (i686-linux-gnu)
    compiled by GNU C version 4.8., GMP version 5.1., MPFR version 3.1.-p3, MPC version 1.0.
GGC heuristics: --param ggc-min-expand= --param ggc-min-heapsize=
Compiler executable checksum: 941e2c230f6d43dfe1ded1af71b0be9d
COLLECT_GCC_OPTIONS='-pthread' '-v' '-mtune=generic' '-march=i686'
 as -v -- -o /tmp/ccLLYbYF.o /tmp/ccH2Lot0.s
GNU assembler version 2.24 (i686-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.24
COMPILER_PATH=/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/4.8/../../../../lib/:/lib/i386-linux-gnu/:/lib/../lib/:/usr/lib/i386-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/i686-linux-gnu/4.8/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-pthread' '-v' '-mtune=generic' '-march=i686'
 /usr/lib/gcc/i686-linux-gnu/4.8/collect2 --sysroot=/ --build-id --eh-frame-hdr -m elf_i386 --hash-style=gnu --as-needed -dynamic-linker /lib/ld-linux.so. -z relro /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crt1.o /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crti.o /usr/lib/gcc/i686-linux-gnu/4.8/crtbegin.o -L/usr/lib/gcc/i686-linux-gnu/4.8 -L/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu -L/usr/lib/gcc/i686-linux-gnu/4.8/../../../../lib -L/lib/i386-linux-gnu -L/lib/../lib -L/usr/lib/i386-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/i686-linux-gnu/4.8/../../.. /tmp/ccLLYbYF.o ../error/error.o -lgcc --as-needed -lgcc_s --no-as-needed -lpthread -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i686-linux-gnu/4.8/crtend.o /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crtn.o

之后一段段分析一下：

首先是给出gcc编译驱动器的整体信息，如版本和配置信息等。注意这里是gcc编译驱动器而不仅仅是编译器（真正编译器是cc1），如下：

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.8/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.8.2-19ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-i386/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-i386 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-i386 --with-arch-directory=i386 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-targets=all --enable-multiarch --disable-werror --with-arch-32=i686 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.8. (Ubuntu 4.8.-19ubuntu1) 

然后打印信息告诉用户将使用真正编译器cc1进行编译，已经调用cc1的一些选项：

/usr/lib/gcc/i686-linux-gnu/4.8/cc1 -quiet -v -imultiarch i386-linux-gnu -D_REENTRANT printids.c -quiet -dumpbase printids.c -mtune=generic -march=i686 -auxbase printids -version -fstack-protector -Wformat -Wformat-security -o /tmp/ccH2Lot0.s

之后打印编译器cc1的版本和配置信息：

GNU C (Ubuntu 4.8.-19ubuntu1) version 4.8. (i686-linux-gnu)
    compiled by GNU C version 4.8., GMP version 5.1., MPFR version 3.1.-p3, MPC version 1.0.
GGC heuristics: --param ggc-min-expand= --param ggc-min-heapsize=128190

接着cc1告诉用户它将搜索那些include文件的路径，并执行编译。如下：

ignoring nonexistent directory "/usr/local/include/i386-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/i686-linux-gnu/4.8/../../../../i686-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/i686-linux-gnu/4.8/include
 /usr/local/include
 /usr/lib/gcc/i686-linux-gnu/4.8/include-fixed
 /usr/include/i386-linux-gnu
 /usr/include
End of search list.
GNU C (Ubuntu 4.8.-19ubuntu1) version 4.8. (i686-linux-gnu)
compiled by GNU C version 4.8., GMP version 5.1., MPFR version 3.1.-p3, MPC version 1.0.
GGC heuristics: --param ggc-min-expand= --param ggc-min-heapsize=
Compiler executable checksum: 941e2c230f6d43dfe1ded1af71b0be9d
COLLECT_GCC_OPTIONS='-pthread' '-v' '-mtune=generic' '-march=i686'

此时已经编译完成得到汇编文件，GCC告诉用户它将调用汇编器as对其进行汇编，打印出它的版本，路径及选项信息。

as -v -- -o /tmp/ccLLYbYF.o /tmp/ccH2Lot0.s
GNU assembler version 2.24 (i686-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.24
COMPILER_PATH=/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i686-linux-gnu/4.8/:/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/:/usr/lib/gcc/i686-linux-gnu/4.8/../../../../lib/:/lib/i386-linux-gnu/:/lib/../lib/:/usr/lib/i386-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/i686-linux-gnu/4.8/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-pthread' '-v' '-mtune=generic' '-march=i686'

当汇编完成后得到了可连接的目标文件，这时需要连接器ld，而gcc使用collect2作为与链接器ld的中间件。如下(链接的详细过程并未打印出来)：

/usr/lib/gcc/i686-linux-gnu/4.8/collect2 --sysroot=/ --build-id --eh-frame-hdr -m elf_i386 --hash-style=gnu --as-needed -dynamic-linker /lib/ld-linux.so. -z relro /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crt1.o /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crti.o /usr/lib/gcc/i686-linux-gnu/4.8/crtbegin.o -L/usr/lib/gcc/i686-linux-gnu/4.8 -L/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu -L/usr/lib/gcc/i686-linux-gnu/4.8/../../../../lib -L/lib/i386-linux-gnu -L/lib/../lib -L/usr/lib/i386-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/i686-linux-gnu/4.8/../../.. /tmp/ccLLYbYF.o ../error/error.o -lgcc --as-needed -lgcc_s --no-as-needed -lpthread -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i686-linux-gnu/4.8/crtend.o /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crtn.o

这里面有一系列"crt"(C runtime )文件，这些文件是用来在你的程序开始和结束位置插入一段代码。代码的作用是初始化你的全局变量，堆栈信息，并且当main返回后，它调用atexit函数返回内核。