As others already said, XS is compiled C code.
There are a few options, depending on what exactly you mean by "checking the code" (I'm assuming Linux here, although most/all of this should also work on Windows with the correct tools installed):
In reply to Re: [B::Deparse] Trying to find sub's code
by cavac
in thread [B::Deparse] Trying to find sub's code
by Gangabass
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