cpp-cheat/glibc/source-tree.md

Source tree

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manual

Documentation

Located under manual/.

sysdeps

Contains both assembly and OS dependant versions of several functions, which makes it one of the most interesting directories.

It contains two kinds of specializations:

• performance, e.g. sysdeps/x86_64/multiarch/memcmp-sse4.S which does memcmp really well for SSE-4

• system call related, which is dependent on the OS used. Linuxers will come again and again to: sysdeps/unix/sysv/linux

  TODO: sysdeps/posix contains many files which are also present in sysdeps/unix/sysv/linux. Why is that? Linux seems to prefer those under sysdeps/unix/sysv/linux, which on the build go to the top-level, e.g. time/clock.o.

• sysdeps/x86_64/dl-machine.h: true entry point, even before _start

Each method also has a pure C implementation when possible, e.g. string/memcmp.c, but that is likely to be much less efficient.

Stub implementations

Basically every directory outside of sysdeps contains only stub implementations of anything that is OS related.

E.g., in posix/getpid.c:

int
__getpid (void)
{
  __set_errno (ENOSYS);
  return -1;
}

which simply sets errno and returns a failure. Then if for a given system there was no implementation, we get ENOSYS as required by POSIX.

sysdep.h

Important header file that gets included into most files of the architecture, most of which are assembly code.

Example:

• sysdeps/x86_64/sysdep.h

It seems that the C preprocessor is used on the assembly code, which does simply #include <sysdep.h>.

multiarch

TODO? as in sysdeps/x86_64/multiarch

elf

mach

Are those the object formats? Why are they needed on an stdlib? Why no PE as well?

csu

TODO? What does it mean? Contains the entry points.

argp

Argument parsing.

Extends POSIX getopt: http://stackoverflow.com/questions/7677562/whats-the-difference-between-argp-and-getopt

io

libio

stdio-common

TODO what is the difference?

Low level IO?

Some things which are in each:

• io: read
• libio: puts
• stdio-common: printf

abilist

TODO

make-syscalls.sh

syscall-template.S

syscalls.list

Generated code for direct system call APIs.