[bug#47921] [PATCH] build: Fix elf-dynamic-info-soname.

[Dion Mendel <guix@dm9.info>]

Thanks for the follow up.

>1. IIUC, this change would cause a world-rebuild, so this patch would 
>have to applied on core-updates.  The subject line should have been
>[PATCH core-updates]: etcetera.

Are you sure?  This patch will modify guix.

   guix graph --type=reverse-package guix

Only shows a few packages to be rebuilt.  I am new to guix so I may be 
wrong about this.

>2. How did you test this patch?

Tested in the repl.

Current behaviour:

    (elf-dynamic-info-soname
      (call-with-input-file "/path/to/libz.so.1.2.11"
                            (compose elf-dynamic-info parse-elf
                                     get-bytevector-all)))
    => #<<dynamic-entry> type: 14 value: "libz.so.1" offset: 5764>

There is no way to extract the value as dynamic-entry is private to the 
module.

After the patch:

    (elf-dynamic-info-soname
      (call-with-input-file "/path/to/libz.so.1.2.11"
                            (compose elf-dynamic-info parse-elf
                                     get-bytevector-all)))
    => "libz.so.1"

>3. What does this patch fix?

Module (guix build gremlin) exports several functions to extract 
information from the dynamic section of an elf file.

elf-dynamic-info-soname is one of these functions.  It is not called 
anywhere in guix.  I would like to use it for packaging, but it is 
currently non functioning.

>4. elf-dynamic-info-soname is a record accessor.  Did you mean 
>elf-dynamic-info?

No, I do not mean elf-dynamic-info.

elf-dynamic-info-soname is a record accessor which is currently broken 
because it doesn't unwrap an internal structure, namely <dynamic-entry>.  
All the other accessors unwrap this internal structure.

This patch brings this accessor into line with the others.

>5. According to the docstring (core-updates, c9a61dff8242612ae8275829a5ee31ff45ff08b1):
>
>  "Return dynamic-link information for ELF as an <elf-dynamic-info> object, or
>#f if ELF lacks dynamic-link information."
>
>  So this patch actually _introduces_ a bug.  Or you need to modify the docstring
>  as well.

No.  This patch does not affect elf-dynamic-info.  It fixes one of its 
accessors.  Nothing else is affected.