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. -- Måns Rullgård m...@mansr.com _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
