Re: Alternative solution to stat storm problem

[Ludovic Courtès]

Hi Farid,

Farid Zakaria <fmzakari@ucsc.edu> skribis:

[...]

>> I guess the advantage is that you don’t need the ld.so patch.  The
>> downside is that PatchELF needs to be able to write longer NEEDED
>> strings in the dynamic section, which it may not always be successful at
>> (I think?).
>
> I can't claim to be a ELF specification guru but I have not
> encountered that longer NEEDED strings to be a cause for failure.
> The emacs example is a pretty good test case because the transitive
> closure of all NEEDED libraries is quite large, which all seem to be
> added successfully to the ELF header.

Well, we’d need a closer look, but I think PatchELF may need to enlarge
the relevant string table, and that may not always be possible.

> The benefit to me seems:
> 1 - does not need a glibc patch for functionality (although for other
> libc such as musl it might in this case
> https://www.openwall.com/lists/musl/2021/12/21/1)
> 2 - understanding the dependencies of an application become simpler
> 3 - there are esoteric cases where in fact libraries might link to the
> wrong libraries (although they are correct at build time) given a
> RUNPATH/RPATH since there are subtleties with the inheritance model.
>
> I'm actually researching ways to improve (3) as well through
> mentorship with Tom Scogland by researching alternative ways to do
> linking:
> - RUNPATH per NEEDED
> - the ability to specify whether a RUNPATH should be inherited or not
> to downstream dependencies

OK.

>> Also, I wonder if the absolute file names in NEEDED interfere with uses
>> of $LD_LIBRARY_PATH (making it impossible to force use of another
>> libxyz.so than the one that would be found in RUNPATH.)
>
> Correct. For a system with reproducibility in mind this can perhaps be
> a desired feature.
> It is the current limitation of the proposal.

I think it’s still useful to allow users to bypass normal mechanisms, be
it via LD_LIBRARY_PATH or LD_PRELOAD.

> In fact, Carlos brought up a great philosophical question:
> "Is linking to libraries through a content-addressable value allowed
> for LGPL software?"
> What if the linked address also forced the content-address by having
> it resolve to something on IPFS ?

Oh you mean it could be thought of a static linking, conceptually?
Good question.

Ludo’.