[RFC PATCH] ld/emulparams: elf32lriscv-defs: Add support tune the text segment start address

[Lad, Prabhakar]

Hi Nelson,

Thank you for the feedback.

On Wed, Dec 21, 2022 at 1:24 PM Nelson Chu <nelson@rivosinc.com> wrote:
>
> On Tue, Dec 20, 2022 at 5:33 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
> >
> > On Mon, 19 Dec 2022 01:11:13 PST (-0800), prabhakar.csengg@gmail.com wrote:
> > > Hi Jeff,
> > >
> > > On Mon, Dec 19, 2022 at 5:00 AM Jeff Law <jeffreyalaw@gmail.com> wrote:
> > >>
> > >>
> > >>
> > >> On 12/18/22 15:44, Lad, Prabhakar via Binutils wrote:
> > >> > Hi Fangrui,
> > >> >
> > >> > Thank you for the feedback.
> > >> >
> > >> > On Sun, Dec 18, 2022 at 6:24 AM Fangrui Song <i@maskray.me> wrote:
> > >> >>
> > >> >> On 2022-12-16, Lad Prabhakar via Binutils wrote:
> > >> >>> On the RISC-V architecture the TEXT_START_ADDR defaults to 0x10000. On
> > >> >>> some RISC-V platforms we want to set this offset to something else. So
> > >> >>> this patch provides a way to tune the text segment start address.
> > >> >>> elf32lriscv-defs.sh now checks for DEFAULT_TEXT_START_ADDR variable and
> > >> >>> if being set it overrides TEXT_START_ADDR to the value set by
> > >> >>> DEFAULT_TEXT_START_ADDR or else defaults to 0x10000.
> > >> >>>
> > >> >>> Renesas RZ/Five RISC-V SoC has Instruction local memory and Data local
> > >> >>> memory (ILM & DLM) which maps between region 0x30000 - 0x4FFFF. When the
> > >> >>> virtual address falls in this range the MMU doesn't trigger a page
> > >> >>> fault and assumes the virtual address as physical address and causes
> > >> >>> undesired behaviours of statically applications/libraries. Hence introduce
> > >> >>> an option to tune the TEXT_START_ADDR.
> > >> >>>
> > >> >>> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > >> >>> ---
> > >> >>> Hi All,
> > >> >>>
> > >> >>> This patch is inspired from the current ld/emulparams/nds32elf_linux.sh file
> > >> >>> where similar approach is being used and DEFAULT_TEXT_START_ADDR variable is
> > >> >>> checked to adjust the TEXT_START_ADDR for the platform.
> > >> >>>
> > >> >>> I am not sure if this is the right approach the above issue has been discussed
> > >> >>> on the ML [0].
> > >> >>>
> > >> >>> [0] https://sourceware.org/pipermail/binutils/2022-November/124813.html
> > >> >>>
> > >> >>> Cheers,
> > >> >>> Prabhakar
> > >> >>> ---
> > >> >>> ld/emulparams/elf32lriscv-defs.sh | 6 +++++-
> > >> >>> 1 file changed, 5 insertions(+), 1 deletion(-)
> > >> >>>
> > >> >>> diff --git a/ld/emulparams/elf32lriscv-defs.sh b/ld/emulparams/elf32lriscv-defs.sh
> > >> >>> index b823cedacab..026aef4714b 100644
> > >> >>> --- a/ld/emulparams/elf32lriscv-defs.sh
> > >> >>> +++ b/ld/emulparams/elf32lriscv-defs.sh
> > >> >>> @@ -27,7 +27,11 @@ case "$target" in
> > >> >>> esac
> > >> >>>
> > >> >>> IREL_IN_PLT=
> > >> >>> -TEXT_START_ADDR=0x10000
> > >> >>> +if [ -z ${DEFAULT_TEXT_START_ADDR+x} ]; then
> >
> > I'm never great with shell expansion, what does the "+x" do here?
>
> I think it should be similar to what nds32 did in the
> ld/emulparams/nds32elf_linux.sh, but I'm not really sure how it works.
> When should the DEFAULT_TEXT_START_ADDR be defined?  Maybe when
> configure or make, not sure about that.  But at least I only see the
> changes in nds32, all of the other targets won't do that, so this must
> be a handy little trick, but there are always other ways to do the
DEFAULT_TEXT_START_ADDR needs to be exported in the shell before doing
configure && make.. For example for testing I bbappended the binutils
yocto recipe and exported the variable in do_configure() so that it
picks up the new offset.

> same things - for example, what maskray said should be the general way
> to do.  I don't have any opinion on this change, if it won't break the
> general build, then probably acceptable.  Just that it seems need to
> introduce the DEFAULT_TEXT_START_ADDR or whatever configure options,
> so this isn't only be the riscv gnu ld's issue, this will also be the
> issue of lld, so if the maintainers of lld already have some
> suggestions, then it will definitely worth to referring to.
>
Is there a mailing list for lld so that we could include them in this
mail thread (I couldn't find one)?

Cheers,
Prabhakar