Re: HEADSUP ABI breakage for future LOCK_PROFILING + non-LOCK_PROFILING usage

On Tuesday 27 February 2007 01:30, Kip Macy wrote:
> The following change will go in shortly unless I hear a good reason
> not to do so.
> 
>            -Kip
> 
> 200702246:
>         The lock_profile_object in the lock_object has been moved to the
>         bottom and lock_object ha been moved to the end of all synchronization
>         primitives so that a kernel compiled without LOCK_PROFILING will
>         work with modules that are compiled with it. It also gets us closer
>         to having a kernel compiled with LOCK_PROFILING work with modules
>         compiled without. The kernel and all modules will need to be
>         re-compiled.

The kernel + modules compiled together should already work if LOCK_PROFILING
is defined when the modules are built, and the new kernel build glue is
supposed to do that for you already.

However, this won't help with mixing the PROFILING and non-PROFILING cases
because 'struct mtx' will still be variant sized and several structures
have 'struct mtx' embedded in them (most notably struct proc) and having
'struct mtx' change size breaks the ABI because the offsets of all the
members after 'p_mtx' change.  E.g. all the p->p_vmspace offsets would be
different in the LOCK_PROFILING vs non-LOCK_PROFILING kernels.

Also, this would break the ddb 'show lock' command, though that may be less
important.

-- 
John Baldwin