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

Simon Glass
2015-02-02T18:15:01Z

Hi Lukasz,

On 2 February 2015 at 01:46, Lukasz Majewski <l.majewski@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.

Regards,
Simon