[PATCH] Valid relocation symbol for FLAT format on ARM

On Wed, Dec 30, 2009 at 06:49:29PM +0000, Jamie Lokier wrote:

Jun Sun wrote:

quoted

   (Sent to linux-kernel, but seems nobody cared. Hopefully someone here
   can pick it up)

I've included uclinux-dev at uclinux.org, because that's where I've seen
most discussion of FLAT format in general.

Thanks. I should have probably done this at the first place.
 

quoted

   Apparently newer GCC would generate ANCHOR symbols beyond the end of
   data/bss segment on ARM CPUs. As a result, the exiting validity checking
   for relocation symbols in FLAT format will fail for some programs.

quoted

-#define        flat_reloc_valid(reloc, size)           ((reloc) <= (size))
+#define        flat_reloc_valid(reloc, size)           ((reloc) <= (size) + 0x1000)

Why 0x1000?  Is that an arbitrary number, or does it have a specific
meaning for GCC?

I had a piece of comment in my first patch submission which explains it
well. I attached it here. This time around I thought for the simplicity
look of code and dropped it. Maybe it should still be there. :)

quoted

   This also fixes a cosmetic error in printk. Text segment and data/bss
   segment are allocated from two different areas. It is not meaningful to
   give the diff between them in error reporting messages.

That part looks fine to me.

-- Jamie

ps. Russell, proof that someone is using no-MMU ARM? :-)

Yes, ARM on no-MMU CPU is still alive. :) Hopefully you can see
some amazing products coming soon that we can all be proud of.

Cheers.

Jun
-------------- next part --------------
diff -Nru linux-2.6.32.2/arch/arm/include/asm/flat.h.orig linux-2.6.32.2/arch/arm/include/asm/flat.h

--- linux-2.6.32.2/arch/arm/include/asm/flat.h.orig	2009-12-18 14:27:07.000000000 -0800
+++ linux-2.6.32.2/arch/arm/include/asm/flat.h	2009-12-26 08:22:43.000000000 -0800

@@ -7,7 +7,12 @@
 
 #define	flat_argvp_envp_on_stack()		1
 #define	flat_old_ram_flag(flags)		(flags)
-#define	flat_reloc_valid(reloc, size)		((reloc) <= (size))
+#define	flat_reloc_valid(reloc, size)		((reloc) <= (size) + 0x1000)
+/* [JSUN] new gcc 4.x generates ANCHOR symbols in order to reduce the size
+ * of GOT table for PIC code. It is possible the ANCHOR is placed beyond
+ * the end of data/bss segment up to 4K bytes(12 bits), because ARM allows
+ * negative 12-bit offset. Thus we allow 0x1000 extra in reloc address range.
+ */
 #define	flat_get_addr_from_rp(rp, relval, flags, persistent) get_unaligned(rp)
 #define	flat_put_addr_at_rp(rp, val, relval)	put_unaligned(val,rp)
 #define	flat_get_relocate_addr(rel)		(rel)

diff -Nru linux-2.6.32.2/fs/binfmt_flat.c.orig linux-2.6.32.2/fs/binfmt_flat.c

--- linux-2.6.32.2/fs/binfmt_flat.c.orig	2009-12-18 14:27:07.000000000 -0800
+++ linux-2.6.32.2/fs/binfmt_flat.c	2009-12-26 08:22:43.000000000 -0800

@@ -355,7 +355,7 @@
 
 	if (!flat_reloc_valid(r, start_brk - start_data + text_len)) {
 		printk("BINFMT_FLAT: reloc outside program 0x%x (0 - 0x%x/0x%x)",
-		       (int) r,(int)(start_brk-start_code),(int)text_len);
+		       (int) r,(int)(start_brk-start_data+text_len),(int)text_len);
 		goto failed;
 	}