[U-Boot] [PATCH v5 2/2] dlmalloc: fix malloc range at end of ram

[Simon Goldschmidt]

Marek Vasut <marek.vasut at gmail.com> schrieb am Fr., 26. Apr. 2019, 00:22:

> On 4/25/19 9:22 PM, Simon Goldschmidt wrote:
> > If the malloc range passed to mem_malloc_init() is at the end of address
> > range and 'start + size' overflows to 0, following allocations fail as
> > mem_malloc_end is zero (which looks like uninitialized).
> >
> > Fix this by subtracting 1 of 'start + size' overflows to zero.
> >
> > Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>
> > ---
> >
> > Changes in v5:
> > - this patch was 1/2 in v4 but is now 2/2 as the 2nd patch of v4 has
> >   already been accepted
> > - rearrange the code to make it only 8 bytes plus in code size for arm
> >   (which fixes smartweb SPL overflowing)
> >
> >  common/dlmalloc.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/common/dlmalloc.c b/common/dlmalloc.c
> > index 6f12a18d54..38859ecbd4 100644
> > --- a/common/dlmalloc.c
> > +++ b/common/dlmalloc.c
> > @@ -601,8 +601,12 @@ void *sbrk(ptrdiff_t increment)
> >  void mem_malloc_init(ulong start, ulong size)
> >  {
> >       mem_malloc_start = start;
> > -     mem_malloc_end = start + size;
> >       mem_malloc_brk = start;
> > +     mem_malloc_end = start + size;
> > +     if (size > mem_malloc_end) {
> > +             /* overflow: malloc area is at end of address range */
> > +             mem_malloc_end--;
>
> Does this mean a memory wrap-around happened ?
> I don't think decrementing malloc area size by 1 is a proper solution.
> You can have it overflow by 2 and decrementing by 1 won't help.
>

No, not a real overflow. Instead, as I tried to described in the commit
message, mem_malloc_end gets 0 if the range is at the end of addr range,
e.g. malloc start is 0xffff0000 and malloc size is 0x10000. Subtracting 1
will be enough here. It reduces the available mall of aize, but I don't
think that should be a problem.

I got this when experimenting with full heap in socfpga. Due to other
patches not being accepted, this is not an issue currebtly, but can easily
become one on the future.

Regrds,
Simon


> > +     }
> >
> >       debug("using memory %#lx-%#lx for malloc()\n", mem_malloc_start,
> >             mem_malloc_end);
> >
>
>
> --
> Best regards,
> Marek Vasut
>