Re: [musl] FDPIC on sh4?

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Rich,

On Thu, Feb 15, 2024 at 2:49 PM Rich Felker <dalias@libc.org> wrote:
> On Thu, Feb 15, 2024 at 04:31:00AM -0600, Rob Landley wrote:
> > Is there any easy way to build FDPIC support for sh4 with-mmu? In theory ARM can
>
> On the userspace toolchain and musl side, yes, I see no reason you
> shouldn't be able to build musl for sh4 with fdpic ABI or build a
> toolchain for sh4 that defaults to fdpic and has fdpic target-libs. I
> just tested passing -mfdpic to sh4-linux-musl-gcc and it seems to
> produce correct fdpic code.
>
> On the kernel side, I'm not sure, but the normal ELF loader should be
> able to load fdpic binaries on a system with mmu. It will not float
> the data segment separately from text, but doesn't need to because it
> has an mmu. If this is no longer working it's a kernel regression;
> that's how I always tested sh2eb fdpic binaries on qemu-system-sh4eb.
>
> > do it, so I tried editing the kconfig BINFMT_ELF_FDPIC dependencies in
> > fs/Kconfig.binfmt to move "SUPERH" out of the !MMU list and put it next to ARM,
> > switched on the FDPIC loader, and the build broke with:
> >
> > fs/binfmt_elf_fdpic.o: in function `load_elf_fdpic_binary':
> > binfmt_elf_fdpic.c:(.text+0x1b44): undefined reference to
> > `elf_fdpic_arch_lay_out_mm'
>
> It looks like there's an arch-provided function that's conditional on
> !MMU in arch/sh but that, now that fdpic loader is intended to be
> supported on mmu-ful systems, should be changed to be conditional on
> fdpic support (or maybe even unconditional if fdpic can be loaded as a
> module). Just look for where it's defined in arch/sh. If it's in a
> nommu-specific file it might need to be moved somewhere more
> appropriate, or an mmu-ful variant may need to be written and placed
> somewhere more appropriate.

ARM is the sole architecture that provides elf_fdpic_arch_lay_out_mm().

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds