[U-Boot] [PATCH 0/3] arm: reduce .bss section clear time

[Tom Rini]

On Thu, Feb 05, 2015 at 10:51:00AM +0100, Lukasz Majewski wrote:
> Hi Simon,
> 
> > Hi Lukasz,
> > 
> > On 2 February 2015 at 01:46, Lukasz Majewski <l.majewski at samsung.com>
> > wrote:
> > > Dear All,
> > >
> > >> And the next is interesting.
> > >>   odroid_defconfig has more than 80MB for malloc (we need about
> > >> 64mb for the DFU now, to be able write 32MB file).
> > >>
> > >> This is the CONFIG_SYS_MALLOC_LEN. And the memory area for malloc
> > >> is set to 0 in function mem_malloc_init(). So for this config that
> > >> function sets more than 80MB to zero.
> > >>
> > >> This is not good, because we shouldn't expect zeroed memory
> > >> returned by malloc pointer. This is a job for calloc.
> > >>
> > >> Especially if some command expects zeroed memory after malloc,
> > >> probably after few next calls - it can crash...
> > >
> > > I think that the above excerpt is _really_ important and should be
> > > discussed.
> > >
> > > I've "cut" it from the original post, so it won't get lost between
> > > the lines.
> > >
> > > It seems really strange, that malloc() area is cleared after
> > > relocation. Which means that all "first" malloc'ed buffers get
> > > implicitly zeroed.
> > >
> > > Przemek is right here that this zeroing shouldn't be performed.
> > >
> > > I'm also concerned about potential bugs, which show up (or even
> > > worse - won't show up soon) after this change.
> > >
> > > Hence, I would like to ask directly the community about the possible
> > > solutions.
> > >
> > > Please look at: ./common/dlmalloc.c mem_alloc_init() function [1].
> > >
> > > On the one hand removing memset() at [1] speeds up booting time and
> > > makes malloc() doing what is is supposed to do.
> > >
> > > On the other hand there might be in space some boards, which rely on
> > > this memset and without it some wired things may start to happening.
> > 
> > I think removing it is a good idea. It was one optimisation that I did
> > for boot time in the Chromium tree. If you do it now (and Tom agrees)
> > then there is plenty of time to test for this release cycle. You could
> > go further and add a test CONFIG which fills it with some other
> > non-zero value.
> 
> Tom, is such approach acceptable for you?

I was thinking at first we should default to a poisoned value.  But
given what we're seeing with generic board updates (lots of boards
aren't even build-tested at every release which isn't really a
surprise), I think the "funky" boards which may exist are probably not
going to be seen for a while anyhow so we'd have to default to a poison
for a long while.  So yes, lets just add a CONFIG option (and Kconfig
line) to optionally do it and default to no memset.

... but I just audited everyone doing "malloc (" and found a few things
to fixup so we really do want to take a poke around.

-- 
Tom
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