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Subjectsizeof problem in kernel modules

Hi !

can someone explain to me whats happening here ?

#include <linux/module.h>
#include <linux/kernel.h>

struct { short x; long y; short z; }bad_struct;
struct { long y; short x; short z; }good_struct;

int init_module(void){
printk("good_struct %d, bad_struct %d\n",sizeof(good_struct),sizeof(bad_struct));
return 0;

void cleanup_module(void){


all: simple.o

CC= gcc
CFLAGS= -pipe -fno-strength-reduce -DCPU=686 -march=i686 \
-Wall -Wstrict-prototypes -g -D__KERNEL__ -DMODULE \
INCLUDE= -I/usr/include/linux

rm -f simple.o


I would expect both structs to be 8byte in size , or atleast the same size !
but good_struct turns out to be 8bytes and bad_struct 12 .

what am I doing wrong here ?

thx !
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