depmod: Unresolved symbols in .../hostap.o: memcmp

[Eric Malkowski]

This smells an aweful lot like a problem I had when building the MADWIFI
driver for my soekris net4826 boards.

With the soekris type kernel config (through i586 instructions only for
the GEODE target), I needed to add a patch to the kernel to export just
memcmp -- memcpy and memset are already exported.  Same problem you're
having.  This was w/ kernel 2.4 -- perhaps the same thing happens w/ 2.6
or perhaps you're also using 2.4

If it's of any help, here's the patch from an older buildroot I was using
at the time:

[malk at miniserv kernel-patches]$ bzcat 101_export-memcmp-for-madwifi.bz2
--- linux-2.4.28-pre4-bvwireless/arch/i386/kernel/i386_ksyms.c  2004-12-27
12:45:06.000000000 -0500
+++ linux-patch/arch/i386/kernel/i386_ksyms.c   2004-12-27
12:47:26.000000000 -0500
@@ -170,10 +170,13 @@

 #undef memcpy
 #undef memset
+#undef memcmp
 extern void * memset(void *,int,__kernel_size_t);
 extern void * memcpy(void *,const void *,__kernel_size_t);
+extern int memcmp(const void *,const void *,__kernel_size_t);
 EXPORT_SYMBOL_NOVERS(memcpy);
 EXPORT_SYMBOL_NOVERS(memset);
+EXPORT_SYMBOL_NOVERS(memcmp);

 #ifdef CONFIG_HAVE_DEC_LOCK
 EXPORT_SYMBOL(atomic_dec_and_lock);
[malk at miniserv kernel-patches]$ pwd
/home/malk/buildroot/package/linux/kernel-patches

For the newer buildroot, you would want to create a patch against your
kernel sources and drop the bzip'd patch under
buildroot/target/device/Soekris/net4521/kernel-patches

An alternative would be to unpack the kernel source that ends up in the dl
directory, modify arch/i386/kernel/i386_ksyms.c to add the 3 lines that
export memcmp for you like my patch above, and re-tar and zip the kernel
source and place it overtop the original in the DL dir and buildroot won't
download it again overwriting the changes.

Then rm -rf build_i386/linux-2.x.x and re-make buildroot and it will just
rebuild the kernel for you.

Then rm -rf build_i386/hostapd and it will rebuild the hostap kernel
module against your new kernel and it can depmod on your build box (suse)
against the symbols that go w/ your target kernel that has memcmp exported
and the problem is solved.

Hope this helps -- I scratched my head for a few hours on that one w/
MADWIFI.  I never determined the root cause for needing to export that
symbol.  Looks like the hostapd kernel module can trigger the same
behavior.

Good luck,

-Eric Malkowski


> Once again, I am looking for pointers for where to look for the source of
> a
> problem.
>
> I am compiling a buildroot environment for a Soekris net4521 target with
> the
> "Generic wireless access point" and "Generic firewall" options turned on.
>
> When I build this, it fails when running depmod.  I am at a loss to
> understand why depmod would complain about not being able to find
> 'memcmp()', when it seems as though it found 'memcpy()', 'memset()',
> etc...
> fine.  What's more confusing is that System.map lists both memcpy and
> memcmp.
>
> Could I have a broken depmod on my build system (a SuSE 9.1 box)?
>
> Is there something obvious I'm missing?
>
> --wpd
>
>