[PATCH] Valid relocation symbol for FLAT format on ARM

Jun Sun
2009-12-31T05:45:07Z

On Wed, Dec 30, 2009 at 06:49:29PM +0000, Jamie Lokier wrote:
> Jun Sun wrote:
> > (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.

> > 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.
>
> > -#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. :)

> > 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;
}