On 03/13/2013 12:03 PM, Måns Rullgård wrote: > Simon Glass <s...@google.com> writes: > >> Hi Mans, >> >> On Wed, Mar 13, 2013 at 3:29 AM, Måns Rullgård <m...@mansr.com> wrote: >>> Tom Rini <tom.r...@gmail.com> writes: >>> >>>> On Tue, Mar 12, 2013 at 7:22 PM, Simon Glass <s...@google.com> wrote: >>>>> Hi, >>>>> >>>>> Given that we seem to allow C99 features in U-Boot I wonder if it >>>>> would be OK to use dynamic arrays in SPL? >>>>> >>>>> I am trying to replace: >>>>> >>>>> ptr = malloc(size); >>>>> >>>>> with: >>>>> >>>>> char ptr[size]; >>>>> >>>>> to avoid use of malloc in SPL. Can I assume that is permitted? >>>> >>>> Without knowing the underlying mechanics of how that works, "maybe". >>> >>> How it works depends on the compiler. Some compilers implement it by >>> calling malloc(). GCC uses the stack. >>> >>> Regardless of how they are implemented, variable-length arrays should, >>> in my opinion, never be used. There is simply no way they can be used >>> safely since no mechanism for detecting failure is provided. If the >>> requested size is too large, you will silently overflow the stack or end >>> up with an invalid/null pointer. In an environment without full memory >>> protection, errors resulting from this are very hard to track down. >> >> I suppose we could check the available stack space. However I don't >> really see a clear stack bottom in U-Boot - I think it is set up to >> grow downwards as much as needed. I can certainly add sanity checks on >> the input values. > > There is no way to check stack usage from C. > >>> If the size is somehow limited to a safe value, it is more efficient to >>> simply allocate this maximum size statically. >> >> Yes although this does waste BSS. > > Sorry, I meant a statically sized stack allocation.
But, there's also no way to detect failure in that case either. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
