On Monday 21 November 2011 14:16:04 David Daney wrote:
> On 11/21/2011 10:50 AM, Mike Frysinger wrote:
> > On Monday 21 November 2011 13:25:36 David Daney wrote:
> >> On 11/20/2011 03:22 PM, Mike Frysinger wrote:
> >>> On Friday 18 November 2011 14:37:44 David Daney wrote:
> >>>> + switch (w2(ehdr->e_machine)) {
> >>>> + default:
> >>>> + fprintf(stderr, "unrecognized e_machine %d %s\n",
> >>>> + w2(ehdr->e_machine), fname);
> >>>> + fail_file();
> >>>> + break;
> >>>> + case EM_386:
> >>>> + case EM_MIPS:
> >>>> + case EM_X86_64:
> >>>> + break;
> >>>> + } /* end switch */
> >>>
> >>> unlike recordmcount, this file doesn't do anything arch specific. so
> >>> let's just delete this and be done.
> >>
> >> Not really true at this point. We don't know the size or layout of the
> >> architecture specific exception table entries, likewise for
> >> CONFIG_ARCH_HAS_SORT_EXTABLE, we don't even know how to do the
> >> comparison.
> >
> > all of your code that i could see is based on "is it 32bit or is it
> > 64bit". there is no code that says "if it's x86, we need to do XXX".
>
> At this point there is no need. MIPS, i386 and x86_64 all store the key
> in the first word of a two word structure.
>
> If there were some architecture that didn't fit this model, we would
> have to create a special sorting function and select it (and perhaps
> other parameters as well) in that switch statement.
that's trivial to check:
sed -n '/^struct exception_table_entry/,/};/p'\
arch/*/include/asm/uaccess* include/asm-generic/uaccess.h
and indeed, the only arches that don't follow this model are the ones that
define ARCH_HAS_SORT_EXTABLE.
> > when i look in the kernel, we have common code behind
> > ARCH_HAS_SORT_EXTABLE. so you could easily do the same thing:
> >
> > scripts/sortextable.c:
> > #ifdef ARCH_HAS_SORT_EXTABLE
> >
> > switch (w2(ehdr->e_machine)) {
> >
> > default:
> > fprintf(stderr, "unrecognized e_machine %d %s\n",
> >
> > w2(ehdr->e_machine), fname);
> >
> > ... return a unique exit code like 77 ...
> > break;
> >
> > /* add arch sorting info here */
> > } /* end switch */
> >
> > #endif
> >
> > kernel/extable.c:
> > #if defined(ARCH_HAS_SORT_EXTABLE)&& !defined(ARCH_HAS_SORTED_EXTABLE)
> > void __init sort_main_extable(void)
> > {
> >
> > sort_extable(__start___ex_table, __stop___ex_table);
> >
> > }
> > #endif
>
> Yes, I am familiar with that code. One thing to keep in mind is that
> the compiler has access to struct exception_table_entry, and can easily
> figure out both how big the structure is *and* where the insn field is
> within the structure.
>
> This is not the case for the author of sortextable. Except for MIPS,
> MIPS64, i386 and x86_64, I know neither the size of struct
> exception_table_entry, nor the offset of its insn field.
a trivial sed/grep gets you the answer: they're all the same
> > this way all the people not doing unique stuff work out of the box. only
> > the people who are doing funky stuff need to extend things.
>
> I didn't want to include something like this that I cannot test. An
> unsorted (or improperly sorted) exception table is not necessarily
> something that will be noticeable by simply booting the kernel. Your
> only indication may be a panic or OOPS under rarely encountered conditions.
this is what linux-next is for :)
-mike
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