error when compiling kernel with some new features - linux-kernel

Question

I am trying to compile kernel version 4.1 with some patches (adding some features to the GRO). I come from a hardware background and relatively new to network stack. I wish to know how to solve this problem or at least pointers to understand why it occurs.
This is what I did
# my temp location
mdkir kern
cd kern
# cloned the juggler and linux 4.1 tree
git clone https://github.com/gengyl08/juggler.git
wget https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.1.tar.gz
tar -xvf linux-4.1.tar.gz
# copied just the essential files that were diffferent
cp juggler/linux-4.1/include/linux/netdevice.h linux-4.1/include/linux/netdevice.h
cp juggler/linux-4.1/include/linux/skbuff.h linux-4.1/include/linux/skbuff.h
cp juggler/linux-4.1/net/core/dev.c linux-4.1/net/core/dev.c
cp juggler/linux-4.1/net/core/net-sysfs.c linux-4.1/net/core/net-sysfs.c
cp juggler/linux-4.1/net/core/skbuff.c linux-4.1/net/core/skbuff.c
cp juggler/linux-4.1/net/ipv4/af_inet.c linux-4.1/net/ipv4/af_inet.c
cp juggler/linux-4.1/net/ipv4/tcp_offload.c linux-4.1/net/ipv4/tcp_offload.c
cd linux-4.1
make menuconfig # generated the default .config file
# building the kernel
time make
When I try to compile them, I get the following error
drivers/net/ethernet/agere/et131x.c: In function ‘nic_send_packet.constprop.43’:
include/linux/compiler.h:412:20: error: call to ‘__compiletime_assert_2439’ declared with attribute error: BUILD_BUG
prefix ## suffix(); \
^
include/linux/compiler.h:417:2: note: in expansion of macro ‘__compiletime_assert’
__compiletime_assert(condition, msg, prefix, suffix)
^
include/linux/compiler.h:429:2: note: in expansion of macro ‘_compiletime_assert’
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^
include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
include/linux/bug.h:74:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^
drivers/net/ethernet/agere/et131x.c:2439:2: note: in expansion of macro ‘BUILD_BUG_ON’
BUILD_BUG_ON(MAX_SKB_FRAGS + 1 > 23);
^
make[4]: *** [drivers/net/ethernet/agere/et131x.o] Error 1
make[3]: *** [drivers/net/ethernet/agere] Error 2
make[2]: *** [drivers/net/ethernet] Error 2
make[1]: *** [drivers/net] Error 2
make: *** [drivers] Error 2
real 22m3.067s
user 21m4.028s
sys 1m6.724s

Answer 1

It looks like MAX_SKB_FRAGS is too big and ethernet driver doesn't like it.
From drivers/net/ethernet/agere/et131x.c:
/* Part of the optimizations of this send routine restrict us to
* sending 24 fragments at a pass. In practice we should never see
* more than 5 fragments.
*/
/* nr_frags should be no more than 18. */
BUILD_BUG_ON(MAX_SKB_FRAGS + 1 > 23);
From the patches you're using:
linux-3.18.5/include/linux/skbuff.h:
#if (65536/PAGE_SIZE + 1) < 16
#define MAX_SKB_FRAGS 16UL
#else
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
#endif
linux-4.1/include/linux/skbuff.h:
#if (65536/PAGE_SIZE + 1) < 45
#define MAX_SKB_FRAGS 45UL
#else
#define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
#endif
Note the difference.
I haven't analyzed this code, but from a very first look I see some inconsistency there.
Replacing 45 back to 16 should do the trick. Of course, there might be a reason why the patch author picked a higher value.