> any idea what's wrong. i've read post 2 months ago about COMPAT_LINUX working 
> on amd64
>
> #   compile  3miasto.net/linux_machdep.o
> cc -mcmodel=kernel -mno-red-zone -ffreestanding -O2 -pipe -Werror -Wall 
> -Wno-main -Wno-format-zero-length -Wpointer-arith -Wmissing-prototypes 
> -Wstrict-prototypes -Wreturn-type -Wswitch -Wshadow -Wcast-qual 
> -Wwrite-strings -Wno-sign-compare -fno-zero-initialized-in-bss -Damd64 
> -Dx86_64 -I. -I../../../../arch -I../../../.. -nostdinc -DMSGMNB=32768 
> -DMSGMNI=41 -DMSGSEG=2048 -DMSGSSZ=64 -DMSGTQL=512 -DKSTACK_CHECK_DR0 
> -DNMBCLUSTERS=32768 -DAPM_POWER_PRINT -DAPM_DISABLE_INTERRUPTS=0 
> -DMAXUSERS=64 -D_KERNEL -D_KERNEL_OPT -I../../../../dist/ipf -c 
> ../../../../compat/linux/arch/amd64/linux_machdep.c
> ../../../../compat/linux/arch/amd64/linux_machdep.c: In function 
> `linux_sendsig':
> ../../../../compat/linux/arch/amd64/linux_machdep.c:261: warning: implicit 
> declaration of function `WCOREDUMP'
> ../../../../compat/linux/arch/amd64/linux_machdep.c:264: warning: implicit 
> declaration of function `_WSTATUS'
> *** Error code 1
>
> Stop.
> make: stopped in /usr/src/sys/arch/amd64/compile/3miasto.net
>
>
fixed.

add
#include <sys/wait.h> to compat/linux/arch/amd64/linux_machdep.c