Re: [PATCH 0/2] riscv: improve __ex_table section handling

Jisheng Zhang
2021-08-26T14:13:09Z

On Wed, 25 Aug 2021 23:47:02 -0700 (PDT)
Palmer Dabbelt <palmer@dabbelt.com> wrote:

> On Sun, 08 Aug 2021 10:25:09 PDT (-0700), jszhang3@mail.ustc.edu.cn wrote:
> > From: Jisheng Zhang <jszhang@kernel.org>
> >
> > Enable BUILDTIME_TABLE_SORT to sort the exception table at build time
> > then move exception table to RO_DATA segment.
> >
> > Jisheng Zhang (2):
> > riscv: Enable BUILDTIME_TABLE_SORT
> > riscv: Move EXCEPTION_TABLE to RO_DATA segment
> >
> > arch/riscv/Kconfig | 1 +
> > arch/riscv/kernel/vmlinux-xip.lds.S | 1 -
> > arch/riscv/kernel/vmlinux.lds.S | 4 ++--
> > scripts/sorttable.c | 1 +
> > 4 files changed, 4 insertions(+), 3 deletions(-)
>
> This seems reasonable, but it's failing for some configurations (at
> least tinyconfig) saying there is no __ex_table. I'm not entirely sure

Nice catch! tinyconfig in riscv means NOMMU which indicates no __ex_table at all.
It seems we have to only enable BUILDTIME_TABLE_SORT for MMU case.

will send out V2 soon.

Thanks

> how that comes about, as we've got them for futexes and uaccess.
>
> Maybe the right thing to do here is to fix scripts/sorttable.c so it can
> handle files with nothing to sort? I think it's just as simple as a
> successful early out like this
>
> diff --git a/scripts/sorttable.h b/scripts/sorttable.h
> index a2baa2fefb13..207ddeddb506 100644
> --- a/scripts/sorttable.h
> +++ b/scripts/sorttable.h
> @@ -294,8 +294,9 @@ static int do_sort(Elf_Ehdr *ehdr,
> goto out;
> }
> #endif
> + /* If there is no __ex_table section there is no work do to. */
> if (!extab_sec) {
> - fprintf(stderr, "no __ex_table in file: %s\n", fname);
> + rc = 0;
> goto out;
> }
>
> I'm not entirely sure though -- my logic is essentially just "there's no
> __ex_table, so there's nothing to sort, so just don't try".
>
> All the configurations I can actually boot have an __ex_table, so I'm
> not sure how to test that.
>
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