Deprecate a.out ELF interpreters

The Linux ELF loader is quite complicated and messy code (that could
probably need a rewrite, but that's a different chapter).  One particular
messy part in it is the support for non ELF a.out ld.sos.  This was
originally added to make transition from a.out to ELF easier because an
a.out ELF ld.so could be still build using an older a.out toolkit.  But by
now that should be fully obsolete and removing it would clean up
binfmt_elf.c up a bit.

I propose to deprecate this support and remove for 2.6.25.

Drawback is that someone still runs their system with a.out ld.so
they would need to update the ld.so when updating to a new kernel.

This patch just adds an entry to the deprecation file and a printk
warning users.

[akpm@linux-foundation.org: better warning message]
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/feature-removal-schedule.txt

@@ -82,6 +82,17 @@ Who:	Dominik Brodowski <linux@brodo.de>
 
 ---------------------------
 
+What:  a.out interpreter support for ELF executables
+When:  2.6.25
+Files: fs/binfmt_elf.c
+Why:   Using a.out interpreters for ELF executables was a feature for
+       transition from a.out to ELF. But now it is unlikely to be still
+       needed anymore and removing it would simplify the hairy ELF
+       loader code.
+Who:   Andi Kleen <ak@suse.de>
+
+---------------------------
+
 What:	remove EXPORT_SYMBOL(kernel_thread)
 When:	August 2006
 Files:	arch/*/kernel/*_ksyms.c

fs/binfmt_elf.c

@@ -730,6 +730,7 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 
 	/* Some simple consistency checks for the interpreter */
 	if (elf_interpreter) {
+		static int warn;
 		interpreter_type = INTERPRETER_ELF | INTERPRETER_AOUT;
 
 		/* Now figure out which format our binary is */
@@ -741,6 +742,13 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 		if (memcmp(loc->interp_elf_ex.e_ident, ELFMAG, SELFMAG) != 0)
 			interpreter_type &= ~INTERPRETER_ELF;
 
+		if (interpreter_type == INTERPRETER_AOUT && warn < 10) {
+			printk(KERN_WARNING "a.out ELF interpreter %s is "
+				"deprecated and will not be supported "
+				"after Linux 2.6.25\n", elf_interpreter);
+			warn++;
+		}
+
 		retval = -ELIBBAD;
 		if (!interpreter_type)
 			goto out_free_dentry;