[PATCH] New -fstack-check implementation

[Richard Guenther]

On Sat, Mar 29, 2008 at 11:14 PM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> Hi,
>
>  Due to popular demand :-), I'm again submitting the new stack checking
>  implementation that we have been using at AdaCore for a few years now.
>
>  Previous submissions:
>   http://gcc.gnu.org/ml/gcc-patches/2006-03/msg01239.html
>   http://gcc.gnu.org/ml/gcc-patches/2006-11/msg01846.html
>
>  But, contrary to the above submissions, this one contains the full set of
>  changes (modulo some adjustments in the Ada runtime and *-unwind.h files for
>  non-Linux platforms).
>
>  -fstack-check is broken in the 4.x series of compilers in the sense that you
>  cannot recover from a stack overflow condition (for example in Ada).  It's a
>  regression from the 3.x series although there were bugs in that series too.
>
>  Moreover, the original implementation comes with several drawbacks:
>  - modified allocation strategy for large objects: they will always be
>  allocated dynamically if their size exceeds a fixed threshold.
>  - fixed limit on the size of the static frame of functions: when it is
>  topped by a particular function, stack checking is not reliable and
>  a warning is issued by the compiler.
>  - inefficiency: because of both the modified allocation strategy and the
>  generic implementation, the performances of the code are unnecessarily
>  hampered.
>
>  We are proposing a new implementation that eliminates the aforementioned
>  drawbacks.  It is based on partial support code in the architecture
>  back-ends, modelled on what the Alpha back-end already has because of the
>  requirement of the Tru64 ABI.

Can you elaborate on the design?  Why do you think we cannot remove the old
code and call -fstack-check unsupported on architectures that do not have
the required target support?

Thanks,
Richard.