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Date: Sun, 30 Mar 2014 19:17:47 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: Any plans on MMU-less support?
On Sun, Mar 30, 2014 at 05:01:39PM +0200, Szabolcs Nagy wrote:
> * Smirnov Vladimir <mapron1@...il.com> [2014-03-30 15:49:08 +0900]:
> > I wonder if MUSL have such roadmap or there is any hackish way to
> > add that support (may be some unoffitial patches).
> > My problem that i've stucked with old gcc toolchain and uClibc
> > supporting one widely used ARMv4 MMUless chip.
>
> looking at uClibc the main differences in a no-mmu system:
>
> fork is not available so related functions have to be changed/disabled
> (vfork, daemon, wordexp, forkpty, pthread_atfork)
vfork does not use fork except as a default implementation when no
arch-specific file exists.
The rest are probably mostly uninteresting to nommu; in any case,
they're not something libc can fix, but things apps must avoid using
to work on nommu.
> brk is not available so malloc needs to change
Thankfully support for the case where brk fails is already on the
agenda due to the kernel bug that affects PIE.
> mmap may need MAP_UNINITIALIZED flag for performance
This is unrelated to libc and gives wrong semantics. If apps want they
can do it, but it's really a bad idea.
> (and MAP_FIXED flag will fail)
Just for MAP_SHARED.
> memory management related things may need to be changed/disabled
> (mprotect?,mlock,msync,..)
Shouldn't affect libc.
> for dynamic linking ldso and libc startup code may need some change
> (some targets (not arm) need fdpic or dsbt elf support)
> (others can use a shared flat binary format)
This is definitely a topic that needs more research. I doubt dynamic
linking could be made to work easily.
> pthread may need smaller default stack and more careful stack usage
This only matters if the machine has a tiny amount of memory; it's
orthogonal to nommu.
> arm startup code needs a change according to
> http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux/arm/crt1.S#n179
This is rather hideous.
Rich
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