Hi,

I'm adding parser and extra map lookup into the xdp1_kern.c and
encounter this LLVM error. My environment:
 clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
 LLVM version 4.0.0svn

I think it might be related to bpf map access, if I comment out the
map access code, then the problem goes away. Looking at similar error
in bcc, I have no clue about how to debug this issue.
https://github.com/iovisor/bcc/issues/220
https://github.com/iovisor/bcc/issues/237
I can share the code if it is more helpful. Any comments are appreciated!

$ clang  -nostdinc -isystem /usr/lib/gcc/x86_64-linux-gnu/5/include
-I./arch/x86/include -I./arch/x86/include/generated/uapi
-I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi
-I./include/uapi -I./include/generated/uapi -include
./include/linux/kconfig.h  \
-D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \
-Wno-compare-distinct-pointer-types \
-Wno-gnu-variable-sized-type-not-at-end \
-Wno-address-of-packed-member -Wno-tautological-compare \
-O2 -emit-llvm -c /root/net-next/samples/bpf/xdp1_kern.c -o -| llc
-march=bpf -filetype=obj -o /root/net-next/samples/bpf/xdp1_kern.o
warning: unknown warning option '-Wno-address-of-packed-member'
[-Wunknown-warning-option]
1 warning generated.
error: couldn't allocate output register for constraint 'r' at line 473618

Thanks
William
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