如何在共享库中嵌入数据？

Question

例如，我想在共享库libxxx.so中嵌入dicmap.bin。我写了一个程序来验证它。

test_dicmap.cpp

#include <stdio.h>
#include <stdint.h>

extern "C" {
extern const uint8_t _binary_dicmap_bin_start[];
extern const uint8_t _binary_dicmap_bin_end[];
extern const void* _binary_dicmap_bin_size;
}

int main()
{
    size_t size = (size_t)&_binary_dicmap_bin_size;
    printf("start=%p, end=%p\nend-start=%zd, size=%zd\n", 
        _binary_dicmap_bin_start, 
        _binary_dicmap_bin_end,
        _binary_dicmap_bin_end - _binary_dicmap_bin_start,
        size);
    printf("data[0..8]=%02x %02x %02x %02x %02x %02x %02x %02x\n", 
            _binary_dicmap_bin_start[0], _binary_dicmap_bin_start[1], 
            _binary_dicmap_bin_start[2], _binary_dicmap_bin_start[3],
            _binary_dicmap_bin_start[4], _binary_dicmap_bin_start[5], 
            _binary_dicmap_bin_start[6], _binary_dicmap_bin_start[7]);
}

但是它的_start、_end和_size是无效的。

]$ ls dicmap.bin  -l
-rw-rw-r-- 1 kirbyzhou kirbyzhou 198600798 Feb 26 10:58 dicmap.bin

]# objcopy -B i386 -I binary -O elf64-x86-64 dicmap.bin dicmap.o && g++ -o libxxx.so dicmap.o -shared  &&  g++ -L. -lxxx  test_dicmap.cpp
/opt/rh/devtoolset-8/root/usr/libexec/gcc/x86_64-redhat-linux/8/ld: warning: type and size of dynamic symbol `_binary_dicmap_bin_size' are not defined
/opt/rh/devtoolset-8/root/usr/libexec/gcc/x86_64-redhat-linux/8/ld: warning: type and size of dynamic symbol `_binary_dicmap_bin_start' are not defined
/opt/rh/devtoolset-8/root/usr/libexec/gcc/x86_64-redhat-linux/8/ld: warning: type and size of dynamic symbol `_binary_dicmap_bin_end' are not defined

]# ./a.out
start=0x601034, end=0x601034
end-start=0, size=6295604
data[0..8]=00 00 00 00 00 00 00 00

结束-开始和大小应为sizeof dicmap.bin (198600798)。

我的objcopy是binutils-2.30-54.el7 of rhel7 with devtoolset-8。

我尝试将共享标志添加到.o文件中，但出现错误：

objcopy -B i386 -I binary -O elf64-x86-64 dicmap.bin dicmap.o --set-section-flag .data=share
objcopy: BFD version 2.30-54.el7 internal error, aborting at elf.c:8869 in _bfd_elf_set_section_contents

objcopy: Please report this bug.

rhel7的binutils-2.27-41.base.el7_7.1.x86_64也有同样的问题。

有什么方法可以帮助我吗？

Answer 1

现在有两个方法对我有效。

方法一:使用objcopy将数据转换为.o，然后链接到.so。然后将".so“和主代码与"-fPIC”链接起来。

objcopy -B i386 -I binary -O elf64-x86-64 dicmap.bin dicmap.o
g++ -shared -fPIC dicmap.o -o libdicmap1.so
# -fPIC is very import in the following line, 
# But it is very unusual when you compile and link main code.
g++ -fPIC test_dicmap.cpp libdicmap1.so -o test_dicmap1-PIC

方法2:使用assmbler对数据进行包装，并以不同的objcopy方式存储大小。

g++ -shared -fPIC dicmap3.s -o libdicmap3.so
g++ test_dicmap3.cpp libdicmap3.so -o test-dicmap3

代码：

test_dicmap.cpp：

#include <stdio.h>
#include <stdint.h>
#include <assert.h>
extern "C" {
extern const uint8_t _binary_dicmap_bin_start[];
extern const uint8_t _binary_dicmap_bin_end[];
extern const void* _binary_dicmap_bin_size;
}
int main()
{
    size_t data_size = (size_t)&_binary_dicmap_bin_size;
    printf("start=%p, end=%p\nend-start=%zd, size=%zd\n", 
        _binary_dicmap_bin_start, 
        _binary_dicmap_bin_end,
        _binary_dicmap_bin_end - _binary_dicmap_bin_start,
        data_size);
    printf("data[0..8]=%02x %02x %02x %02x %02x %02x %02x %02x\n", 
            _binary_dicmap_bin_start[0], _binary_dicmap_bin_start[1], 
            _binary_dicmap_bin_start[2], _binary_dicmap_bin_start[3],
            _binary_dicmap_bin_start[4], _binary_dicmap_bin_start[5], 
            _binary_dicmap_bin_start[6], _binary_dicmap_bin_start[7]);
    assert(_binary_dicmap_bin_end - _binary_dicmap_bin_start == data_size);
}

test_dicmap3.cpp：

#include <stdio.h>
#include <stdint.h>
#include <assert.h>

extern "C" {
extern const uint8_t _binary_dicmap_bin_start[];
extern const uint8_t _binary_dicmap_bin_end[];
extern const size_t _binary_dicmap_bin_size;
}


int main()
{
    size_t data_size = _binary_dicmap_bin_size;
    printf("start=%p, end=%p\nend-start=%zd, size=%zd\n", 
        _binary_dicmap_bin_start, 
        _binary_dicmap_bin_end,
        _binary_dicmap_bin_end - _binary_dicmap_bin_start,
    data_size);
    printf("data[0..8]=%02x %02x %02x %02x %02x %02x %02x %02x\n",
            _binary_dicmap_bin_start[0], _binary_dicmap_bin_start[1], 
            _binary_dicmap_bin_start[2], _binary_dicmap_bin_start[3],
            _binary_dicmap_bin_start[4], _binary_dicmap_bin_start[5], 
            _binary_dicmap_bin_start[6], _binary_dicmap_bin_start[7]);
    // _binary_dicmap_bin_end is invalid
    //assert(_binary_dicmap_bin_end - _binary_dicmap_bin_start == data_size);
}

dicmap3.s：

    .globl  _binary_dicmap_bin_start
    .globl  _binary_dicmap_bin_end
    .globl  _binary_dicmap_bin_size
    .section  .rodata
    .type   _binary_dicmap_bin_start, @object
    .align  8
_binary_dicmap_bin_start:
    .incbin "dicmap.bin"
    .align  1
    .size   _binary_dicmap_bin_end, 1
_binary_dicmap_bin_end:
    .byte   0
    .size   _binary_dicmap_bin_start, _binary_dicmap_bin_end - _binary_dicmap_bin_start
    .type   _binary_dicmap_bin_size, @object
    .size   _binary_dicmap_bin_size, 8
    .align  8
_binary_dicmap_bin_size:
    .quad   _binary_dicmap_bin_end - _binary_dicmap_bin_start

dicmap.bin：

helloworld