Mcrt1.o和Scrt1.o有什么用途？

Question

我卡在了以下两个文件的使用上，它们分别是Mcrt1.o和Scrt1.o。有谁能帮我知道这两个文件是做什么的？如何使用它们？以gcrt1.o为例，当编译时加上-pg选项进行性能测试时非常有用。谢谢。

- Daniel

Answer 1

形如*crt*.o的文件通常是C运行时启动代码（大部分C运行时存在于库中，启动代码是一个目标文件，因为它总是需要的）。

各种类型的描述可以在这里找到，在下面复制以使答案自包含。首先是一些定义：

Mini FAQ about the misc libc/gcc crt files.

Some definitions:
  PIC - position independent code (-fPIC)
  PIE - position independent executable (-fPIE -pie)
  crt - C runtime

然后是各种启动对象文件：

crt0.o
  Older style of the initial runtime code ?  Usually not generated anymore
  with Linux toolchains, but often found in bare metal toolchains.  Serves
  same purpose as crt1.o (see below).
crt1.o
  Newer style of the initial runtime code.  Contains the _start symbol which
  sets up the env with argc/argv/libc _init/libc _fini before jumping to the
  libc main.  glibc calls this file 'start.S'.
crti.o
  Defines the function prolog; _init in the .init section and _fini in the
  .fini section.  glibc calls this 'initfini.c'.
crtn.o
  Defines the function epilog.  glibc calls this 'initfini.c'.
Scrt1.o
  Used in place of crt1.o when generating PIEs.
gcrt1.o
  Used in place of crt1.o when generating code with profiling information.
  Compile with -pg.  Produces output suitable for the gprof util.
Mcrt1.o
  Like gcrt1.o, but is used with the prof utility.  glibc installs this as
  a dummy file as it's useless on linux systems.

还有其他一些：

crtbegin.o
  GCC uses this to find the start of the constructors.
crtbeginS.o
  Used in place of crtbegin.o when generating shared objects/PIEs.
crtbeginT.o
  Used in place of crtbegin.o when generating static executables.
crtend.o
  GCC uses this to find the start of the destructors.
crtendS.o
  Used in place of crtend.o when generating shared objects/PIEs.

最后，常用的链接顺序：

General linking order:
  crt1.o crti.o crtbegin.o [-L paths] [user objects] [gcc libs]
    [C libs] [gcc libs] crtend.o crtn.o

- paxdiablo

---

我不知道在什么情况下我们会使用Scrt1.o而不是crt1.o？ - Daniel