Re: [Xen-devel] [PATCH v2] xen/arm: Correctly support WARN_ON

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 08/09/14 06:01, Ian Campbell wrote:
> > +    /* PC is always 4-byte align, as Xen is using ARM instruction set */
> "aligned"
Ok.

> Is it worth a check here? I presume the nested fault if PC were
> misaligned would be pretty exciting, print+goto die would seem
> appropriate.
I don't think so. The "undefined instruction" is only used when the 
processor is unable to decode the instruction. If it fails to load the 
instruction (because a wrong memory address, pc misaligned), Xen would 
have received a "prefetch abort".
> > +    instr = *((uint32_t *)regs->pc);
> > +    if ( instr != BUG_OPCODE )
> > +        goto die;
> > +
> > +    if ( do_bug_frame(regs, regs->pc) )
> > +        goto die;
> > +
> > +    regs->pc += 4;
> > +    return;
> > +
> > +die:
> > +    do_unexpected_trap("undefined instruction", regs);
> No need to change the case of this message.
Ok.

> >   }> +#ifdef CONFIG_ARM_64
> > +static void do_trap_brk(struct cpu_user_regs *regs, union hsr hsr)
> > +{
> > +    /* HCR_EL2.TGE and MDCR_EL2.TDE are not set so we never receive
> > +     * software breakpoint exception for EL1 and EL0 here
> > +     */
> BUG_ON? ;-O
Sounds a good plan.

> > +die:
> > +        do_unexpected_trap("undefined breakpoint value", regs);
> Please can you capitilise this to match the other callers.
Will do.

> > +/* Many version of GCC doesn't support the asm %c parameter which would
> "versions".
>
> > + * be preferable to this unpleasantness. We use mergeable string
> > + * sections to avoid multiple copies of the string appearing in the
> > + * Xen image.
> OOI what is the size increase of the final (stripped) binary with this patch?
        
I compared the file xen/xen and on both arm32/arm64 the binary is 
smaller of about 2%.
I think this is because previously gcc wasn't merge the string when 
BUG_ON was used in inline function.
Regards,

--
Julien Grall

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