Re: [PATCH] Document jit_align.

[Marc Nieper-Wißkirchen]

Thank you for your help!

I won't be able to work on it within the next two weeks. But then I
will take a closer look at it.

Marc

Am Mi., 17. Aug. 2022 um 15:24 Uhr schrieb Paulo César Pereira de
Andrade <paulo.cesar.pereira.de.andrade@gmail.com>:
>
> Em ter., 16 de ago. de 2022 às 15:25, Marc Nieper-Wißkirchen
> <marc@nieper-wisskirchen.de> escreveu:
> >
> > Am Di., 16. Aug. 2022 um 20:14 Uhr schrieb Paulo César Pereira de
> > Andrade <paulo.cesar.pereira.de.andrade@gmail.com>:
> > >
> > > Em dom., 14 de ago. de 2022 às 13:09, Marc Nieper-Wißkirchen
> > > <marc@nieper-wisskirchen.de> escreveu:
> > > >
> > > > I just noticed that the argument to jit_align is asserted to be at most 
> > > > as large as the size of a word in jit_x86.c (line 1596).  To make 
> > > > jit_align suitable for what the documentation was written for, the 
> > > > limit should be increased to, say, jit_get_max_instr().  For that, the 
> > > > nop generator in jit_x86-cpu.c has to be modified to allow longer 
> > > > sequences of nop (e.g. by iterating).
> > >
> > >   The idea for jit_align was indeed just to make it just align jump 
> > > targets
> > > or function prologs.
> > >   Usually jumps to aligned addresses are faster.
> > >
> > >   The assertions should be changed.
> >
> > I am going to put this on my TODO list as this involves improving the
> > nop-generators in the jit_xxx-cpu.c files. For that, I need the
> > 128-bit opcode for a NOP on ia64.
>
>   First need to call sync(), which is commented a bit before the 
> jit_code_align
> switch. The sync() function will flush any pending code generation. I do not
> recall checking this, but maybe should always do it in a jit_code_align().
>   It already calls sync() for jit_code_label, so, should not be required.
>
>   About a 128 bit NOP, it should be, after a sync(), the sequence:
> NOP_M(0), NOP_I(0), NOP_I(0)
> some other variants should work, but the above should be the simplest.
> Obviously, need to fool proof check it.
>
> > Marc