Can we know the definition of the function in GDB? - gdb

Question

I am learning gdb to make life little easier. I searched Google for this but couldn't find the answer. Though I learned that $1 is a gdb variable that can be used later anywhere in the debugging. But for my question there is no info.
Code:
if (pthread_create (&mythread[i], NULL, (void *)threadFunction,(void *) i))
{
printf ("\nerror creating thread");
exit (1);
}
My question is - can I see the definition of threadFunction or pthread_create function assuming gdb knows it.

Answer 1

GDB uses debug information, often in DWARF format, which contains names -e.g. of local variables-, source locations (source path, line number), etc.... That debug information exists for code compiled with -g (passed to GCC compiler). So you can get source location information for every code compiled with -g (and you could recompile yourself with -g the libraries you are using). Most of the time that DWARF info sits in the same shared library or object file (in ELF format) but there is some way to keep it in a separate file.
pthread_create is a C standard library POSIX function (it is using system calls such as clone(2); see syscalls(2) for an exhaustive list). Read carefully the pthread_create(3) documentation. On Linux most C standard libraries (notably GNU glibc and musl-libc) are free software, so you can study their source code. You may need to find a debug variant of your libc, e.g. some libc-dbg Debian package.
can I see the definition of threadFunction
You can use the list command of GDB. So try list threadFunction (assuming that the source code containing its definition was compiled with -g).
... or of pthread_create
The definition of pthread_create (provided by your C standard library) would appear only if you use a libc compiled with debug info. It may be faster to browse its source code (e.g. src/thread/pthread_create.c of
musl-libc) than to recompile your entire libc with debug info.
To understand the behavior of pthread_create you may want to understand clone(2), but it is better to trust the documentation in pthread_create(3). Most of it (of clone) is implemented inside the Linux kernel, which is also free software (downloadable on kernel.org). You could spend many years in understanding all the details (but ask also on kernelnewbies.org after having begin to study some kernel code).
Many Linux distributions are mostly made of free software, totalizing more than ten billions lines of source code. You surely need more than a lifetime to study most of them. Abstraction is practically essential in software development (so choose what details you are willing to forget). Read also about undefined behavior and about leaky abstractions.
Read also Advanced Linux Programming (a bit old) and Operating Systems : Three Easy Pieces. Both are freely downloadable. https://computing.llnl.gov/tutorials/pthreads/ is a good tutorial on Posix Threads Programming.