4. Patches and binaries

At this point in the proceedings, you can, if you like, stop. You have installed everything necessary to compile and run ELF programs.

You may wish to rebuild programs in ELF, either for purposes of `neatness' or to minimise memory usage. For most end-user applications, this is pretty simple; some packages however do assume too much about the systems they run on, and may fail due to one or more of:

• Different underscore conventions in the assembler: in an a.out executable, external labels get _ prefixed to them; in an ELF executable, they don't. This makes no difference until you start integrating hand-written assembler: all the labels of the form _foo must be translated to foo, or (if you want to be portable about it) to EXTERNAL(foo) where EXTERNAL is some macro which returns either its argument (if __ELF__ is defined) or _ concatenated with its argument if not.
• Differences in libc 5 from libc 4. The interface to the locale support has changed, for one.
• The application or build process depending on knowledge of the binary format used --- emacs, for example, dumps its memory image to disk in executable format, so obviously needs to know what format your executables are in.
• The application consists of or includes shared libraries (X11 is the obvious example). These will obviously need changes to accomodate the different method of shared library creation in ELF.

Anyway, here are two lists: the first is of programs that needed changing for ELF where the changes have been made (i.e. that you will need new versions of to compile as ELF), and the second is of programs that still need third-party patches of some kind.

4.1 Upgrade:

• Dosemu. Nowadays, dosemu runs with ELF. You'll need to monkey with the Makefile. Current versions of dosemu are available from ftp://tsx-11.mit.edu/pub/linux/ALPHA/dosemu/
• e2fsutils. The Utilities for the Second Extended File System versions 0.5c and later compile unchanged in ELF.
• Emacs. There are two potential problems here. (i) Emacs has a rather odd build procedure that involves running a minimal version of itself, loading in all the useful bits as lisp, then dumping its memory image back to disk as an executable file. (FSF) Emacs 19.29 and XEmacs 19.12 (formerly Lucid Emacs) can both detect whether you are compiling as ELF and Do The Right Thing automatically. (ii) If you build some versions of emacs against ncurses, it will fail unless you first edit src/s/linux.h in the emacs distribution to add the line #define TERMINFO somewhere near the top. This is not necessary for 19.31, but is for XEmacs 19.13. Apparently it will be fixed in 19.14.
• gdb 4.16. Your existing copy of gdb will continue to work just as well as it always has done in the past, but the shared library support in 4.16 is a lot better, so if you want to debug programs that do weird things in that area, this is a good upgrade.
• The Kernel. Kernel versions 2.0 and greater work fine with ELF; you have to say `yes' to both of

  Kernel support for ELF binaries (CONFIG_BINFMT_ELF) [Y/m/n/?]
  Compile kernel as ELF - if your GCC is ELF-GCC (CONFIG_KERNEL_ELF) [Y/n/?]
  

  when you run make config (this is also the case for most of the 1.3 series). If you are using 1.2 still, see the `patch' list below.
• perl 5. Perl 5.001m and later will compile unchanged on an ELF system, complete with dynamic loading. Current versions of Perl are available from CPAN (Comprehensive Perl Archive Network) sites: see ftp://ftp.funet.fi/pub/mirrors/perl/CPAN for the closest one to you.
• ps and top. Procps 0.98 and greater will work with ELF (earlier versions also work, but can't read the kernel to find WCHAN names, if you care about them). Note that 2.0 series kernels require procps 0.99a or greater anyway.
• The cal program in util-linux 2.2 doesn't work. Upgrade to version 2.5 or later.
• Mosaic. I don't have the facilities to build this myself, but the Mosaic 2.7b1 binary available from NCSA comes in ELF. It has been linked against an odd X setup though, with the result that on normal systems it will complain about not finding libXpm.so.4.5. The simple fix is to edit it carefully with emacs or another editor that copes with binary files. Find the occurence of the string libXpm.so.4.5ˆ@ (where ˆ@ is a NUL --- ASCII zero --- character), delete the .5 and add two more characters after the NUL to aviod changing the file length.

4.2 Patch

• file. This works anyway, but can be improved: ftp://ftp.uk.linux.org/pub/Linux/libc/non-core/file.patch adds support for identifying stripped and mixed-endian ELF binaries.
• make-3.74 --- either get the source code from a GNU site and apply the patch that comes with the libc-5.3.12 release notes, or get the binary make-3.74.gz from tsx-11. There is a bug in GNU make which only manifests with new ELF libc versions --- it's actually a dependency on a bug in old versions of the GNU libc, which was also present in Linux libc until recently. If you keep your old a.out make program it will continue to work, but if you want an ELF one you need the patch. The GNU Make developers know about the bug, and one day will release a fixed version.
• The 1.2.x Kernel. You have three options:
  1. Patch the Makefile slightly to use the a.out compiler. cd /usr/src/linux/, cut the following patch out, and feed it into patch -p1. Or just edit the Makefile manually using this as a guide; it's clear enough (delete the lines marked with a - and add the ones with a +.

     diff -u linux-1.2.13/Makefile.orig linux/Makefile
     --- linux-1.2.13/Makefile.orig  Wed Aug 16 20:53:26 1995
     +++ linux/Makefile      Fri Dec  8 16:19:49 1995
     @@ -12,9 +12,9 @@
      TOPDIR := $(shell if [ "$$PWD" != "" ]; then echo $$PWD; else pwd; fi)
     
     -AS     =as
     -LD     =ld
     -HOSTCC =gcc -I$(TOPDIR)/include
     -CC     =gcc -D__KERNEL__ -I$(TOPDIR)/include
     +AS     =/usr/i486-linuxaout/bin/as
     +LD     =ld  -m i386linux
     +HOSTCC =gcc -b i486-linuxaout -I$(TOPDIR)/include
     +CC     =gcc -b i486-linuxaout -D__KERNEL__ -I$(TOPDIR)/include
      MAKE   =make
      CPP    =$(CC) -E
      AR     =ar
     

     Alternatively,
  2. Apply H J Lu's patch which allows compiling the kernel in ELF (and also adds the ability to do ELF core dumps). This can be had from ftp://ftp.cdrom.com/pub/linux/slackware_source/kernel-source/v1.2/linuxelf-1.2.13.diff.gz. If you are using an ELF distribution (RedHat 2.1, Slackware 3) which comes with a 1.2 series kernel, you will probably find that this patch or one similar has been applied already. The best idea, hoever, is probably
  3. Upgrade to 2.0! 1.2 was never really intended for ELF anyway.
  You will have other problems compiling 1.2.13 with gcc 2.7.2 and above; there was a bug in asm/io.h which is only detected by gcc 2.7.2. You will need the patch ftp://ftp.uk.linux.org/pub/Linux/libc/misc/io.h.