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List:       hpux-devtools
Subject:    Re: HPUX-DEVTOOLS: shared library?
From:       Eric Gouriou <egouriou () cup ! hp ! com>
Date:       2002-08-08 22:30:57
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"Rajiv K. Shukla" wrote:
> Use of 'dlopen' is undesirable, so is the use of
> 'file' command. For now, simple c code based on
> /etc/magic serves the purpose. Unfortunately, it's not
> very portable.

* For Elf shared libraries (PA64 or IPF ILP32 / LP64),
  use /usr/include/elf.h .

 The important elements are:
  1) Check e_ident
   char e_ident[EI_NIDENT];

   is_elf = (   (ELFMAG0 == e_ident[EI_MAG0])
             && (ELFMAG1 == e_ident[EI_MAG1])
             && (ELFMAG2 == e_ident[EI_MAG2])
             && (ELFMAG3 == e_ident[EI_MAG3]));

  2) If is_elf, read the Elf header (Elf<N>_Ehdr type)

     Watch for Elf64 vs Elf32 formats (which are
     _not_ necessarily linked to 32bit / 64bit ABIS)
     See EI_CLASS in e_ident (ELFCLASS32 / ELFCLASS64)
 
     Watch for endianness and byte-swap if necessary.
     See EI_DATA in e_ident (ELFDATA2LSB / ELFDATA2MSB)

     Read e_type.

     Then:  e_type  ->  ET_DYN   shared library
                        ET_EXEC  executable
                        others (.o , etc)

 This should be pretty portable, but I am no expert
on object formats.

* For SOM files (to check for HP-UX PA32 shared libraries),
use /usr/include/filehdr.h, read the header content and
the fields check system_id and a_magic. Unfortunately I
don't know where/if the relevant constants are officially
documented, however you could piece this together from
/etc/magic:

   system_id   0x20b -> PA1.0
               0x210 -> PA1.1
               0x214 -> PA2.0
   a_magic     0x10E -> shared library


 Obviously those checks can be fooled but a lot of
tools / the runtime will be unhappy if a file passes
those checks but isn't a shared library.

 I hope this helps. No guarantee.

 Eric

-- 
Eric Gouriou                             egouriou@cup.hp.com
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