[fpc-devel] Re: Bug in revision 9781/2
daniel.mantione at freepascal.org
Sat Jan 19 16:52:09 CET 2008
Op Sat, 19 Jan 2008, schreef Marc Weustink:
> Daniël Mantione wrote:
>> Op Sat, 19 Jan 2008, schreef Jonas Maebe:
>>> On 19 Jan 2008, at 15:54, Peter Vreman wrote:
>>>> This call and pop is old-style PIC and not good for new cpus because it
>>>> breaks the call-stack. Please use the new style that calls a function
>>>> (fpc_geteipasebx). This also generated by the compiler. See
>>>> i386/cgcpu.pas and search for g_maybe_got_init.
>>> I recently read that on the more recent processors, call/pop is slightly
>>> faster again (I suppose they detect a call to next instruction and don't
>>> add it to the internal call stack or so).
>> Intel cpu's since Pentium M and AMD cpu's since Barcelona indeed have a
>> stack analyzer. I'm still going to switch back to the fpc_geteipasebx
>> helper since the extra call/ret penalty on those processors is small while
>> the penalty of a broken call stack is large.
> Just for my information, this callstack, is it "tracked" by the CPU or
> generated by FPC. I somehow fail to see why a call&pop will affect the
> callstack in case it is generated.
It is tracked by the cpu. It exists to prevent the pipeline has to be
flushed when encountering a ret; with the call stack the cpu can know
where the program will continue.
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