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Re: The direction of malloc?
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Siddhesh Poyarekar <siddhesh at redhat dot com>
- Cc: Will Newton <will dot newton at linaro dot org>, Carlos O'Donell <carlos at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>, Roland McGrath <roland at hack dot frob dot com>, Andreas Jaeger <aj at suse dot com>, Andreas Schwab <schwab at suse dot de>, OndÅej BÃlka <neleai at seznam dot cz>
- Date: Tue, 10 Dec 2013 17:00:10 +0000
- Subject: Re: The direction of malloc?
- Authentication-results: sourceware.org; auth=none
- References: <52A6A0DA dot 1080109 at redhat dot com> <CANu=Dmi32gwk-hQ3dDbj0d4_gs3FWqt02+NmveXH1p03Vm+Mfg at mail dot gmail dot com> <20131210111031 dot GH5048 at spoyarek dot pnq dot redhat dot com>
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