The direction of malloc?

[Joseph S. Myers]

On Tue, 10 Dec 2013, Siddhesh Poyarekar wrote:

> A really cool feature would be to have the ability to plug in malloc
> implementations at least at build time in the beginning and then later
> at runtime using tunables.  It should be doable by implementing a
> layer that passes calls on to the selected implementation.  This would
> have to be implemented using relocation (IFUNC?) since otherwise we're
> introducing an additional cost.

Applications can always provide their own malloc, as can an LD_PRELOAD 
library; calls from libc to malloc functions should already go through the 
PLT so as to get any replacement malloc.

One significant difficulty with building a replacement into glibc is 
supporting malloc_set_state calls with data saved with a previous glibc 
version - the problem that has so far prevented us from correcting malloc 
alignment for powerpc32 without breaking emacs (bug 6527 - as noted in 
that bug, it should be fixed for 32-bit x86 as well to support ISO C 
extensions such as _Decimal128 properly, if a way to fix it is found).

-- 
Joseph S. Myers
joseph@codesourcery.com