Re: [PATCH v3 2/3] Add an optional "alias" attribute to syscall entries.

[Eli Zaretskii <eliz@gnu.org>]

> Cc: gdb-patches@sourceware.org
> From: John Baldwin <jhb@FreeBSD.org>
> Date: Fri, 16 Nov 2018 09:43:56 -0800
> 
> > IMO, this is very abstract and too vague to be useful.  Since we won't
> > have anything more detailed in the manual, would it be possible to
> > make this description more concrete?  E.g., how about using some of
> > the text and examples you used in your description of the issue:
> 
> Ok.  I wasn't too happy with my first attempt either.  I've tried to give
> some more detail while not making it too long.  Let me know what you think:
> 
> * System call catchpoints now support system call aliases on FreeBSD.
>   When the ABI of a system call changes in FreeBSD, this is
>   implemented by leaving a compatibility system call using the old ABI
>   at the existing number and allocating a new system call number for
>   the new ABI.  For example, FreeBSD 12 altered the layout of 'struct
>   kevent' used by the 'kevent' system call.  As a result, FreeBSD 12
>   kernels ship with both 'kevent' and 'freebsd11_kevent' system calls.
>   The 'freebsd11_kevent' system call is assigned an alias of 'kevent'
>   so that a system call catchpoint for the 'kevent' system call will
>   catch invocations of both the 'kevent' and 'freebsd11_kevent'
>   binaries.  This ensures that 'kevent' system calls are caught for
>   binaries using either the old or new ABIs.

LGTM, thanks.