Re: [PATCH] binfmt_flat: Remove shared library support

Damien Le Moal
2022-04-20T23:00:48Z

On 4/21/22 05:23, Rich Felker wrote:
> On Wed, Apr 20, 2022 at 10:04:32PM +0200, Arnd Bergmann wrote:
>> On Wed, Apr 20, 2022 at 7:47 PM Kees Cook <keescook@chromium.org> wrote:
>>>
>>> Yeah, I was trying to understand why systems were using binfmt_flat and
>>> not binfmt_elf, given the mention of elf2flat -- is there really such a
>>> large kernel memory footprint savings to be had from removing
>>> binfmt_elf?
>>
>> I think the main reason for using flat binaries is nommu support on
>> m68k, xtensa and risc-v. The regular binfmt_elf support requires
>> an MMU, and the elf-fdpic variant is only available for arm and sh
>> at this point (the other nommu architectures got removed over time).
>
> I believe I made the elf-fdpic loader so that it's capable of loading
> normal non-fdpic elf files on nommu (1bde925d23), unless somebody
> broke that. I also seem to recall that capability being added to the
> main elf loader later.

Last time I checked, building shared libraries usable with nommu riscv
required gcc/ld options that were not supported for riscv (PIE related
stuff). So removing the kernel support for shared flat libs is fine with me.

--
Damien Le Moal
Western Digital Research