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

[John Baldwin <jhb at FreeBSD dot org>]

On 11/28/18 4:19 AM, Pedro Alves wrote:
> On 11/27/2018 09:53 PM, John Baldwin wrote:
>> +On some operating systems, a system call name may map to more than one
>> +system call number.  For example, the FreeBSD kernel allocates new
>> +system call numbers when changing the ABI of an existing system call.
>> +The kernel also includes a compatibility system call using the old ABI
>> +and number.  FreeBSD's system call XML file includes aliases for
>> +compatibility system calls that are used to catch all versions of a
>> +system call.  For example, FreeBSD 12 introduced a new variant of the
>> +@code{kevent} system call.  Both system calls are caught when catching
>> +the @code{kevent} system call:
>> +
>> +@smallexample
>> +(@value{GDBP}) catch syscall kevent
>> +Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
>> +(@value{GDBP})
>> +@end smallexample
>> +
> 
> I'd suggest replacing "FreeBSD's system call XML file includes" with
> something else that isn't so implementor-speak.  Users needn't
> be aware of the XML file.  Maybe something along the lines of
> "GDB is aware of aliases for compatibility system calls that
> are used to catch ..."  Or maybe remove the sentence altogether.
> Maybe simplify it a bit further, as users don't really need
> to be told that that's what FreeBSD does for all new syscalls,
> just that some syscalls are like that.  I think.  Thus, something
> like this is enough, IMHO:
> 
> 
> On some operating systems, a system call name may map to more than one
> system call number.  
> 
> For example, FreeBSD 12 introduced a new variant of the @code{kevent} system
> call, and included a compatibility system call using the old ABI and number.
> As convenience, both system calls are caught when catching the @code{kevent}
> system call by name:
> 
> @smallexample
> (@value{GDBP}) catch syscall kevent
> Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
> (@value{GDBP})
> @end smallexample

Yes, I think this is better as well.  Eli, I don't know if other OS's will
make use of this feature.  Given Pedro's new text above, do you think it
should still be moved into a native section or should it stay in the the
syscall section?

-- 
John Baldwin