[pypy-dev] PPC stacklet switching code

[Armin Rigo]

Hi Vaibhav,

On Wed, Oct 14, 2015 at 11:26 AM, Vaibhav Sood
<vaibhav_sood at persistent.com> wrote:
> code to return back to the calling function slp_switch. However in between
> the calling function’s stack content is overwritten by the g_restore_state
> code (it memcpy’s the stored heap memory data to the stack) causing the
> saved LR value to be destroyed and thus returning from the g_restore_state
> function (using blr) causes a segfault

I would decrement sp around the two calls to the C functions,
g_save_state and g_restore_state, to give them their own temporary
places to write to without interference.  This is similar to how the
x86 version gives "rsp" as argument, but then uses CALL, which pushes
the return address just below rsp, i.e. out of scope of the
saving/restoring.  Example:

...
mr     r3, sp            # the 1st argument is the value of sp without
the extra space
stdu   sp, -64(sp)   # decrement sp again; 64 should be enough
...call g_save_state...
addi   sp, sp, 64     # restore sp
...


A bientôt,

Armin.