[PATCH] malloc: Deprecate hook variables, __default_morecore, <mcheck.h>

[Florian Weimer]

On 11/15/2016 04:39 PM, Joseph Myers wrote:
> On Tue, 15 Nov 2016, Florian Weimer wrote:
>
>> In my opinion, the larger ecosystem already provides suitable replacements.
>>
>> * <mcheck.h> and all malloc hook functions are now deprecated.  Future
>>   implementations of the mcheck- and mtrace-related functions will not
>>   have any effect, and glibc will stop calling the hook functions from
>>   its malloc implementation.  Instead of mcheck and mtrace, developers
>>   should consider using valgrind.  As a replacement for the hook
>>   functions, developers can interpose their own malloc implementation.
>
> I don't consider valgrind suitable for replacing the uses of mtrace in the
> glibc testsuite (or other similar uses elsewhere for lightweight checking
> for leaks).

I completely agree.

The above is for the NEWS file, for external use.  For internal use, we 
still need a solution.  (I have an mtrace-compatible interposition-based 
tracer almost finished, but it may not make the cut for the next 
release, and it may be superseded by DJ's work anyway.)  I think we can 
run internal deprecation at a different pace than external deprecation.

> I don't know enough about the functionality GDB expects from linking with
> -lmcheck by default in development to know whether other malloc
> improvements would provide similar checking by default or whether that
> would also need GDB to provide its own malloc (again, I think valgrind is
> vastly too heavyweight for using by default in GDB development).

I wasn't aware that GDB developers are using this functionality.  I'll 
ask them how critical it is to their needs.  But I expect that there 
will be no glibc release which neither provides mcheck, nor provides an 
alternative.

Thanks,
Florian