[Toybox] imgtec patch: Fix static linkage of toybox binary.

[Evgenii Stepanov]

Does https://android-review.googlesource.com/#/c/223875/ look OK?
It disables the stack depth check if toybox is configured with no recursion.


On Sat, May 7, 2016 at 11:30 AM, enh <enh at google.com> wrote:
> On Fri, May 6, 2016 at 10:58 PM, Rob Landley <rob at landley.net> wrote:
>> On 05/07/2016 12:16 AM, Evgenii Stepanov wrote:
>>> Sorry, I did not look at the problem hard enough.
>>> The real issue is interaction of this code with safestack
>>> (http://clang.llvm.org/docs/SafeStack.html), which splits the stack in
>>> 2 disjoint memory regions. If the two variables are allocated on
>>> different stacks, the comparison result is truly undefined.
>>>
>>> I don't really understand what this code is tying to do. Is it
>>> catching unlimited stack growth? Why does the comment speak about
>>> heap?
>>
>> It's a heuristic that enables an optimization. You could select
>> CONFIG_TOYBOX_NORECURSE to disable this optimization.
>
> i thought we were still using that, but it looks like i undid my
> setting of that option here:
> https://googleplex-android.git.corp.google.com/platform/external/toybox/+/a729fc8373ade0ced1cd0dd5ad43ef6a61a5cd24
>
> https://android-review.googlesource.com/223514 (unsubmitted) turns it
> back on, since that might be easier than trying to come up with a
> heuristic that works well in a SafeStack world. as long as we're still
> using mksh i don't think it matters much anyway.
>
>> The help text of that option describes it a little: when one toybox
>> command calls another, it can either recurse into the new command's
>> main() function, or call the actual execve() to relaunch the toybox
>> binary with a fresh environment. Recursing is much faster, but has the
>> downside that if you do enough in a row you tend to accumulate debris
>> (open filehandles and unfreed mallocs and such from being halfway
>> through another program). (Plus if you do it _forever_, you'll actualy
>> run out of stack.) So it checks how much stack we've used as a simple
>> heuristic to see whether we should recurse or should exec.
>>
>> This heuristic has not been particularly tuned, that's one of my toysh
>> todo items. (toysh is likely to be the heaviest user.)
>>
>> Rob
>
>
>
> --
> Elliott Hughes - http://who/enh - http://jessies.org/~enh/
> Android native code/tools questions? Mail me/drop by/add me as a reviewer.