*

Linux下对Alignment trap的处理有下面几种方式：

0 (ignored)

1 (warn)

2 (fixup)

3 (fixup+warn)

4 (signal)

5 (signal+warn)

使用方法：

# echo 3 > /proc/cpu/alignment

*/

#include <stdio.h>

#include <stdlib.h>

/// case 1

void fool(unsigned char* buf, int len)

{

unsigned int* p = (unsigned int*)buf;

int i;

for (i = 0; i < len; i++)

{

*p++ = i+1;

printf(“%d “, *p);

}

}

void foolish()

{

unsigned char poor[100];

fool(poor, sizeof(poor)/sizeof(int));

}

// case 1 end

////////////////////////////////////////////////////////////////

/// case 2

struct rte_unpacked_struct_t

{

char c1;

int i;

char c2;

short s1;

char c3;

};

struct rte_packed_struct_t

{

char c1;

int i;

char c2;

short s1;

char c3;

}__attribute__((__packed__));

struct rte_unpacked_struct_t unpacked;

struct rte_packed_struct_t packed;

void print_addr()

{

printf(“sizeof(unpacked) = %d sizeof(packed) = %d\n”, sizeof(unpacked), sizeof(packed));

printf(“Addr of unpacked: %p\n”, &unpacked);

printf(“Addr of unpacked.c1: %p\n”, &unpacked.c1);

printf(“Addr of unpacked.i: %p\n”, &unpacked.i);

printf(“Addr of unpacked.c2: %p\n”, &unpacked.c2);

printf(“Addr of unpacked.s1: %p\n”, &unpacked.s1);

printf(“Addr of unpacked.c3: %p\n”, &unpacked.c3);

printf(“Addr of packed: %p\n”, &packed);

printf(“Addr of packed.c1: %p\n”, &packed.c1);

printf(“Addr of packed.i: %p\n”, &packed.i);

printf(“Addr of packed.c2: %p\n”, &packed.c2);

printf(“Addr of packed.s1: %p\n”, &packed.s1);

printf(“Addr of packed.c3: %p\n”, &packed.c3);

}

short* rte_get_s1(void)

{

return &unpacked.s1;

}

void case2()

{

print_addr();

int* val = (int *)rte_get_s1();

printf(“val = %d\n”, *val);

}

/// case 2 end

////////////////////////////////////////////////////////////////

/// case 3

struct foo_t

{

short a;

short b;

short c;

short d;

};

struct foo_t foo;

short* get_foo_c(void)

{

return &foo.c;

}

void case3()

{

printf(“sizeof(foo) = %d\n”, sizeof(foo));

    // 注意！！此处将short*强制转换为int*，造成出错

int* val = (int *)get_foo_c();

printf(“val: %d\n”, *val);

}

// case 3 end

//////////////////////////////////////////////////////////////

/// case 4

void case4()

{

char* str = “01234567”;

unsigned* u = (unsigned *)(str+1);

printf(“0x%08x\n”, *u);

}

/// case 4 end

int main()

{

printf(“test of alignment trap…\n”);

//foolish();

//case2();

//case3();

case4();

return 0;

}

# ./a.out 

test of alignment trap…

0x30333231

# echo 1 >  /proc/cpu/alignment 

# ./a.out 

testAlignment trap: a.out (1125) PC=0x000086c8 Instr=0xe5931000 Address=0x00008961 FSR 0x001

of alignment trap…

0x30333231

# echo 2 >  /proc/cpu/alignment 

# ./a.out 

test of alignment trap…

0x34333231

# echo 3 >  /proc/cpu/alignment 

# ./a.out 

testAlignment trap: a.out (1127) PC=0x000086c8 Instr=0xe5931000 Address=0x00008961 FSR 0x001

of alignment trap…

0x34333231

# echo 4 >  /proc/cpu/alignment 

# ./a.out 

test of alignment trap…

Bus error

# echo 5 >  /proc/cpu/alignment 

# ./a.out 

testAlignment trap: a.out (1129) PC=0x000086c8 Instr=0xe5931000 Address=0x00008961 FSR 0x001

of alignment trap…

Bus error