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Re: The direction of malloc?
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Will Newton <will dot newton at linaro dot org>
- Cc: Siddhesh Poyarekar <siddhesh at redhat dot com>, 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>, Ondřej Bílka <neleai at seznam dot cz>
- Date: Tue, 10 Dec 2013 18:04:04 +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> <Pine dot LNX dot 4 dot 64 dot 1312101654500 dot 15324 at digraph dot polyomino dot org dot uk> <CANu=Dmi5mr9z4P99LDB+8q6_1XcNraeofyScgFdwqOhZMBTTGQ at mail dot gmail dot com>
On Tue, 10 Dec 2013, Will Newton wrote:
> > 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).
> Is that actually possible? I thought malloc_get_state just returned an
> opaque pointer so I wasn't aware it could be written out to any kind
> of storage or last longer than the lifetime of a process.
The main purpose of malloc_get_state / malloc_set_state is for use by
emacs. If emacs adopted a better approach I'd happily deprecate them -
turn them into compat symbols - but you still need to support them
indefinitely with existing emacs binaries, as a matter of binary
compatibility. (Support could mean such binaries - binaries using the
malloc_set_state compat symbol - use a different copy of malloc in libc
from what all other binaries use, if necessary.)
Joseph S. Myers