On Fri, Dec 22, 2023 at 6:02 PM Helge Deller <deller@xxxxxx> wrote:
>
> On 12/21/23 14:07, Masahiro Yamada wrote:
> > On Thu, Nov 23, 2023 at 7:18 AM <deller@xxxxxxxxxx> wrote:
> >>
> >> From: Helge Deller <deller@xxxxxx>
> >>
> >> On 64-bit architectures without CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
> >> (e.g. ppc64, ppc64le, parisc, s390x,...) the __KSYM_REF() macro stores
> >> 64-bit pointers into the __ksymtab* sections.
> >> Make sure that the start of those sections is 64-bit aligned in the vmlinux
> >> executable, otherwise unaligned memory accesses may happen at runtime.
> >
> >
> > Are you solving a real problem?
>
> Not any longer.
> I faced a problem on parisc when neither #1 and #3 were applied
> because of a buggy unalignment exception handler. But this is
> not something which I would count a "real generic problem".
>
> > 1/4 already ensures the proper alignment of __ksymtab*, doesn't it?
>
> Yes, it does.
>
> >...
> > So, my understanding is this patch is unneeded.
>
> Yes, it's not required and I'm fine if we drop it.
>
> But regarding __kcrctab:
>
> >> @@ -498,6 +501,7 @@
> >> } \
> >> \
> >> /* Kernel symbol table: Normal symbols */ \
> >> + . = ALIGN(4); \
> >> __kcrctab : AT(ADDR(__kcrctab) - LOAD_OFFSET) { \
> >> __start___kcrctab = .; \
> >> KEEP(*(SORT(___kcrctab+*))) \
>
> I think this patch would be beneficial to get proper alignment:
>
> diff --git a/include/linux/export-internal.h b/include/linux/export-internal.h
> index cd253eb51d6c..d445705ac13c 100644
> --- a/include/linux/export-internal.h
> +++ b/include/linux/export-internal.h
> @@ -64,6 +64,7 @@
>
> #define SYMBOL_CRC(sym, crc, sec) \
> asm(".section \"___kcrctab" sec "+" #sym "\",\"a\"" "\n" \
> + ".balign 4" "\n" \
> "__crc_" #sym ":" "\n" \
> ".long " #crc "\n" \
> ".previous" "\n")
Yes!
Please send a patch with this:
Fixes: f3304ecd7f06 ("linux/export: use inline assembler to populate
symbol CRCs")
--
Best Regards
Masahiro Yamada
