Re: [Qemu-devel] [PATCH 05/10] tcg/mips: use stack for TCG temps

[Aurelien Jarno]

On Sat, Sep 22, 2012 at 02:37:35PM +0000, Blue Swirl wrote:
> On Fri, Sep 21, 2012 at 4:43 PM, Aurelien Jarno <address@hidden> wrote:
> > Use stack instead of temp_buf array in CPUState for TCG
> > temps.
> >
> > Signed-off-by: Aurelien Jarno <address@hidden>
> > ---
> >  tcg/mips/tcg-target.c |   10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
> > index 0ea6a76..c05169f 100644
> > --- a/tcg/mips/tcg-target.c
> > +++ b/tcg/mips/tcg-target.c
> > @@ -1538,11 +1538,15 @@ static void tcg_target_qemu_prologue(TCGContext *s)
> >  {
> >      int i, frame_size;
> >
> > -    /* reserve some stack space */
> > +    /* reserve some stack space, also for TCG temps. */
> >      frame_size = ARRAY_SIZE(tcg_target_callee_save_regs) * 4
> > -                 + TCG_STATIC_CALL_ARGS_SIZE;
> > +                 + TCG_STATIC_CALL_ARGS_SIZE
> > +                 + CPU_TEMP_BUF_NLONGS * sizeof(long);
> >      frame_size = (frame_size + TCG_TARGET_STACK_ALIGN - 1) &
> >                   ~(TCG_TARGET_STACK_ALIGN - 1);
> > +    tcg_set_frame(s, TCG_REG_SP, ARRAY_SIZE(tcg_target_callee_save_regs) * 
> > 4
> > +                  + TCG_STATIC_CALL_ARGS_SIZE,
> > +                  CPU_TEMP_BUF_NLONGS * sizeof(long));
> 
> My version used frame_size instead of duplicating a part of the
> calculations, wouldn't that take stack alignment also in
> consideration?
> 
> http://lists.nongnu.org/archive/html/qemu-devel/2011-06/msg02566.html

Oh haven't seen this patch before. Well the choice is basically between
adding one value and subtracting one, not sure what is the best.

About the alignment, do we require some specific alignment for the
temps? As long as they are aligned wrt size, I think it's fine.

> >
> >      /* TB prologue */
> >      tcg_out_addi(s, TCG_REG_SP, -frame_size);
> > @@ -1597,6 +1601,4 @@ static void tcg_target_init(TCGContext *s)
> >      tcg_regset_set_reg(s->reserved_regs, TCG_REG_GP);   /* global pointer 
> > */
> >
> >      tcg_add_target_add_op_defs(mips_op_defs);
> > -    tcg_set_frame(s, TCG_AREG0, offsetof(CPUArchState, temp_buf),
> > -                  CPU_TEMP_BUF_NLONGS * sizeof(long));
> >  }
> > --
> > 1.7.10.4
> >
> >
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net