On Thu, Oct 17, 2013 at 11:58:43AM -0700, Christoffer Dall wrote:
> On Thu, Oct 17, 2013 at 12:38:59PM +0200, Andrew Jones wrote:
> > On Wed, Oct 16, 2013 at 06:06:42PM -0700, Christoffer Dall wrote:
> > > > +++ b/arm/cstart.S
> > > > @@ -1,5 +1,6 @@
> > > >
> > > > #define CR_B (1 << 7)
> > > > +#define CR_V (1 << 13)
> > > >
> > > > .arm
> > > >
> > > > @@ -12,6 +13,13 @@ start:
> > > > push { r0-r3 } @push r3 too for 8-byte
> > > > alignment
> > > >
> > > > mrc p15, 0, r8, c1, c0, 0 @r8 = sctrl
> > > > +
> > > > + /* set up vector table */
> > > > + bic r8, #CR_V @sctrl.V = 0
> > > > + mcr p15, 0, r8, c1, c0, 0
> > > > + ldr r0, =vector_table @vbar = vector_table
> > > > + mcr p15, 0, r0, c12, c0, 0
> > > > +
> > > > bl get_endianness
> > > > bl io_init
> > > >
> > > > @@ -41,6 +49,44 @@ halt:
> > > > 1: wfi
> > > > b 1b
> > > >
> > > > +vector_common:
> > > > + add r2, sp, #(14 * 4)
> > >
> > > this looks weird, what are you pointing to here?
> >
> > What sp was at the time of exception. So if you look at ex_regs->sp,
> > then you'll see what sp was when the exception occurred, not that plus
> > what we're pushing on now for the handler.
> >
>
> Hmmm, so you're assuming that all exceptions will be taken from SVC
> mode? I assume we will run tests in more than SVC mode, no?
>
> Also note that the lr you're pushing here is not the lr at the time the
> exception occurs, but the return address from the exception. If the SVC
> instruction is executed from SVC mode, the original lr is lost iirc, and
> the caller needs to save it. If you're from user mode, something like
>
> stm sp, {r0-lr}^
>
> will take care of this for you, and if you're from svc
> mode, you may want consider doing something like
>
> push {sp, lr}
> push {r0-r12}
>
> instead (assuming this is only ever compiled in ARM mode, not Thumb2, in
> which case the whole thing gets more complicated.
I think the lr pushing should be ok. That part is done in the macro that
all vectors start with. It got snipped from this mail, so here it is
.macro m_vector, v
push { r0-r12,lr }
mov r1, \v
b vector_common
.endm
I realize it may still not be correct, just as the calculated sp
may not be correct, depending on which mode,vector combo is used,
but I was expecting to have different paths in the C code for
fixing it up. Although that said, I haven't thought about it a
bunch yet, so maybe it won't work that way...
drew
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