c - Mcrt1.o和Scrt1.o有什么用？

Question

我坚持使用以下两个文件，即 Mcrt1.o 和 Scrt1.o。谁能帮我知道这两个文件是干什么用的。如何使用它？我们以 gcrt1.o 为例，它在编译时使用 -pg 选项进行性能测试非常有用。谢谢

Answer 1

形式*crt*.o的文件总是 C 运行时启动代码（大部分 C 运行时往往存在于库中，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，复制到下面以使答案自成一体。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

然后是各种启动目标文件：

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，常见的链接顺序：

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