When I assigned a static global pointer, segmentation fault occurred

Question

I try to implement a toy malloc,and my code crashed at list_head = header in

#define ADDR_ADD(a, o) (((char*)(a)) + o)
#define HEADER_SIZE (sizeof(heap_header))

static heap_header* list_head = NULL;

int mini_crt_heap_init()
{
        void* base = NULL;
        heap_header* header = NULL;
        unsigned heap_size = 1024 * 1024 * 32;

        base = (void*)brk(0);
        void* end = ADDR_ADD(base, heap_size);
        end = (void*)brk(end);
        if(!end) return 0;

        header = (heap_header*)base;
        header->size = heap_size;
        header->type = HEAP_BLOCK_FREE;
        header->next = NULL;
        header->prev = NULL;

        list_head = header;
        return 1;
}

In GDB,the pointer header gets the value of the pointer base, and I also make some assignments on header and they all work. However, when it goes to list_head = header,the program crashed.

The screenshot of gdb: base,end,header and list_head

My question is that if I can't access the address,it should crash at header->size = heap_size;, which is a normal segfault. But it goes well until list_head = header;

I haven't got any idea why segmentation fault occurred, and how can I handle this problem and make it run? Is there any problem with my makefile?

The struct of heap_header:

typedef struct _heap_header
{
        enum{
                HEAP_BLOCK_FREE = 0xABABABAB,
                HEAP_BLOCK_USED = 0xCDCDCDCD,
        } type;
        unsigned size;
        struct _heap_header *next;
        struct _heap_header *prev;
}heap_header;

My brk():

//Linux brk system call
static int brk(void* end_data_segment)
{
        int ret = 0;
        asm("movl $45, %%eax     \n\t"
                "movl %1 , %%ebx \n\t"
                "int $0x80       \n\t"
                "movl %%eax, %0  \n\t"
                : "=m"(ret)
                : "m"(end_data_segment)
                );
        return ret;
}

Additional makefile

STATIC_SRC = malloc.c stdio.c string.c

STATIC_OBJ = $(patsubst %.c,%.o,$(STATIC_SRC))

CFLAGS =  -c -fno-builtin -nostdlib -fno-stack-protector -m32

static:
        gcc -g $(CFLAGS) $(STATIC_SRC) entry.c
        ar -rs minicrt.a $(STATIC_OBJ)

test:
        gcc -g $(CFLAGS) test.c
        ld -static -melf_i386 -e mini_crt_entry entry.o test.o minicrt.a -o test
all: static test

clean:
        rm -f *.o *.a test core*