Re: [PATCH] Restore module support.

[Russell King <rmk@arm.linux.org.uk>]

On Fri, Feb 07, 2003 at 03:53:44PM +1100, Rusty Russell wrote:
> Yes.  PPC and PPC64 have the same issues: currently this is done by
> (1) putting nothing in the .init sections (on PPC64), and (2) with
> stubs when jumping outside the module code.
> 
> This gives the same effect as the previous userspace loader: for PPC64
> noone cares about discarding init stuff, so it's firmly on the TODO
> list.  ARM's priorities are obviously different.

As I say, I have this solution working, but its suboptimal, and I'll
probably push this Linus-wards if I can't resolve (2) soon.

> > 2. fix vmalloc and /proc/kcore to be able to cope with a separate module
> >    region located below PAGE_OFFSET.  Currently, neither play well with
> >    this option.
> 
> x86_64 has this, as does sparc64: they do their own allocation.  Does
> ARM require something special in this regard?  I'd love to see what
> you've got...

There are two problems - one I mentioned during on LKML recently:

  Message-ID: <20030131102013.A19646@flint.arm.linux.org.uk>

This seems simple to resolve.  We just need to make get_vm_area() ignore
mappings for invalid areas:

--- orig/mm/vmalloc.c	Tue Nov  5 12:51:41 2002
+++ linux/mm/vmalloc.c	Fri Feb  7 09:48:42 2003
@@ -210,6 +210,8 @@
 
 	write_lock(&vmlist_lock);
 	for (p = &vmlist; (tmp = *p) ;p = &tmp->next) {
+		if (tmp->addr < addr)
+			continue;
 		if ((size + addr) < addr)
 			goto out;
 		if (size + addr <= (unsigned long)tmp->addr)

Since the vmlist is an ordered list, and we place the modules below
VMALLOC_START, this change ensures that we will completely ignore any
vmlist entries below the current minimum address (addr) we're looking
for.

/proc/kcore currently assumes that:

1. all vmlist mappings are above PAGE_OFFSET.
2. all vmlist mappings are within VMALLOC_START to VMALLOC_END

Looking at fs/proc/kcore.c this morning, I have a couple of ideas to
solve this problem.  Patch will follow later today, hopefully without
any ifdefs.

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html