making changes in libc

[asenat dadon]

greetings
my name is Asenat dadon and i"m a phd student at the Ben-Gurion
University Israel.
im sending to you this email since the message i sent to the
libc-alpha mail returned several times

in my research I would like to make some changes in the libc.
specifically I would like to be able to add and modify some
functionality.

In general I need to perform some actions on several libc wrapper
functions, before calling them. for example i would like to send a
message to some entity before calling to the exec family calls, write,
read and so on.

during my search for the code of the libc i found this site:
https://code.woboq.org/userspace/glibc. nevertheless I don't know how
to relate to it. specifically, I find the code of the exec functions
but i could not find where the sysentry interrupt is performed.

I would appreciate it very much if you could advise me on how to find
the required functions, such as exec, open etc.

in addition to that, i would like to add a specific function that some
of the functions will know how to call it, and i will appreciate it
very much if you could assist me in that as well

thank you in advance
asnat