[Python-Dev] Handling linker scripts reached when dynamically loading a module

[Guido van Rossum]

Excuse me for asking a newbie question, but what are linker scripts
and why are they important? I don't recall anyone ever having
requested this feature before.

--Guido

On Wed, Sep 7, 2011 at 12:33 PM, Howard B. Golden
<howard_b_golden at yahoo.com> wrote:
> Hi,
>
> In Haskell I experienced a situation where dynamically loaded modules
> were experiencing "invalid ELF header" errors. This was caused by the
> module names actually referring to linker scripts rather than ELF
> binaries. I patched the GHC runtime system to deal with these scripts.
>
> I noticed that this same patch has been ported to Ruby and Node.js, so I
> suggested to the libc developers that they might wish to incorporate the
> patch into their library, making it available to all languages. They
> rejected this suggestion, so I am making the suggestion to the Python
> devs in case it is of interest to you.
>
> Basically, when a linker script is loaded by dlopen, an "invalid ELF
> header" error occurs. The patch checks to see if the file is a linker
> script. If so, it finds the name of the real ELF binary with a regular
> expression and tries to dlopen it. If successful, processing proceeds.
> Otherwise, the original "invalid ELF error" message is returned.
>
> If you want to add this code to Python, you can look at my original
> patch (http://hackage.haskell.org/trac/ghc/ticket/2615) or the Ruby
> version (https://github.com/ffi/ffi/pull/117) or the Node.js version
> (https://github.com/rbranson/node-ffi/pull/5) to help port it.
>
> Note that the GHC version in GHC 7.2.1 has been enhanced to also handle
> another possible error when the linker script is too short, so you might
> also want to add this enhancement also (see
> https://github.com/ghc/blob/master/rts/Linker.c line 1191 for the
> revised regular expression):
>
> "(([^ \t()])+\\.so([^ \t:()])*):([ \t])*(invalid ELF header|file too
> short)"
>
> At this point, I don't have the free time to write the Python patch
> myself, so I apologize in advance for not providing it to you.
>
> HTH,
>
> Howard B. Golden
> Northridge, California, USA
>
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-- 
--Guido van Rossum (python.org/~guido)