On Wed, Apr 20, 2022 at 12:59:37PM -0400, Rich Felker wrote: > On Wed, Apr 20, 2022 at 09:17:22AM -0700, Palmer Dabbelt wrote: > > On Wed, 20 Apr 2022 07:58:03 PDT (-0700), ebiederm@xxxxxxxxxxxx wrote: > > > > > >In a recent discussion[1] it was reported that the binfmt_flat library > > >support was only ever used on m68k and even on m68k has not been used > > >in a very long time. > > > > > >The structure of binfmt_flat is different from all of the other binfmt > > >implementations becasue of this shared library support and it made > > >life and code review more effort when I refactored the code in fs/exec.c. > > > > > >Since in practice the code is dead remove the binfmt_flat shared libarary > > >support and make maintenance of the code easier. > > > > > >[1] https://lkml.kernel.org/r/81788b56-5b15-7308-38c7-c7f2502c4e15@xxxxxxxxxxxxxx > > >Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > > >--- > > > > > >Can the binfmt_flat folks please verify that the shared library support > > >really isn't used? > > > > I don't actually know follow the RISC-V flat support, last I heard it was still > > sort of just in limbo (some toolchain/userspace bugs th at needed to be sorted > > out). Damien would know better, though, he's already on the thread. I'll > > leave it up to him to ack this one, if you were even looking for anything from > > the RISC-V folks at all (we don't have this in any defconfigs). > > For what it's worth, bimfmt_flat (with or without shared library > support) should be simple to implement as a binfmt_misc handler if > anyone needs the old shared library support (or if kernel wanted to > drop it entirely, which I would be in favor of). That's how I handled > old aout binaries I wanted to run after aout was removed: trivial > binfmt_misc loader. 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? But regardless, yes, it seems like if you're doing anything remotely needing shared libraries with binfmt_flat, such a system could just use ELF instead. -- Kees Cook
