How to create alias for particular (new/existing) function in glibc - c

Question

For some reasons I wish to create alias to function
pthread_mutex_trylock(pthread_mutex_t *mutex);
from the glibc to alias named
lab_pthread_mutex_trylock(pthread_mutex_t *mutex);
I try add
weak_alias (__pthread_mutex_trylock, lab_pthread_mutex_trylock)
in the file pthread_mutex_trylock.c (editing source code of the library) and then
./configure --prefix=/home/user/glibc
make
make install
After that I compile my program like
gcc \
-L "/home/user/glibc/lib" \
-I "/home/user/glibc/include" \
-Wl,--rpath="/home/user/glibc/lib" \
-Wl,--dynamic-linker="/home/user/glibc/lib/ld-linux-x86-64.so.2" \
-std=c11 \
-o main.out \
-v \
main.c \
-pthread \
;
ldd ./main.out
./main.out
The ldd script show me that some functions (from default libc) are really from my build of glibc, but use lab_pthread_mutex_trylock(pthread_mutex_t *mutex) causes error.
glibc has very complicated structure and I have quite weak knowledge about build management so I feel that lot of things I should to do was missed by me. Please, help me, it's very important for me...
Error by gcc:
gcc -L "/ home / anahel / glibc-test / lib" -I "/ home / anahel / glibc-test / include" -Wl, - rpath = "/ home / anahel / glibc-test / lib" -Wl , - dynamic-linker = "/ home / anahel / glibc-test / lib / ld-linux-x86-64.so.2" -std = c11 -o main.out main.c -pthread
/ usr / bin / ld: /tmp/ccivqLEz.o: in the "main" function:
main.c :(. text + 0x1b): undefined reference to "lab_pthread_mutex_trylock"
collect2: error: ld returned 1 exit status
The steps I did in glibc sources:
1) If file glibc-2.31/nptl/pthread_mutex_trylock.c I added
weak_alias (__pthread_mutex_trylock, lab_pthread_mutex_trylock)
2) In file glibc-2.31/sysdeps/nptl/pthread.h I added
extern int lab_pthread_mutex_trylock (pthread_mutex_t *__mutex)
__THROWNL __nonnull ((1));
right after
/* Try locking a mutex. */
extern int pthread_mutex_trylock (pthread_mutex_t *__mutex)
__THROWNL __nonnull ((1));

Answer 1

This error:
undefined reference to "lab_pthread_mutex_trylock"
means that the lab_pthread_mutex_trylock is not exported from /home/user/glibc/lib/libpthread.so.0. You can confirm this with:
nm -D /home/user/glibc/lib/libpthread.so.0 | grep lab_pthread_mutex_trylock
(expect no output if my guess is correct).
The likely reason it's not exported: GLIBC build process tightly controls which functions are exported, and what version they have, via a linker script (which is generated by combining several Version files).
In particular, you very likely need to add lab_pthread_mutex_trylock to the glibc-2.31/nptl/Versions file.