Question

在linux中，在文件dl-machine.h中有以下函数来获取共享对象的运行时加载地址。这也适用于FreeBSD，或者有不同的方法吗？

/* Return the run-time load address of the shared object.  */
static inline ElfW(Addr) __attribute__ ((unused))
elf_machine_load_address (void)
{
  ElfW(Addr) addr;

  /* The easy way is just the same as on x86:
   leaq _dl_start, %0
   leaq _dl_start(%%rip), %1
   subq %0, %1
 but this does not work with binutils since we then have
 a R_X86_64_32S relocation in a shared lib.

 Instead we store the address of _dl_start in the data section
 and compare it with the current value that we can get via
 an RIP relative addressing mode.  Note that this is the address
 of _dl_start before any relocation performed at runtime.  In case
 the binary is prelinked the resulting "address" is actually a
 load offset which is zero if the binary was loaded at the address
 it is prelinked for.  */

  asm ("lea _dl_start(%%rip), %0\n\t"
   "sub 1f(%%rip), %0\n\t"
   ".section\t.data.rel.ro\n"
   "1:\t" ASM_ADDR " _dl_start\n\t"
   ".previous\n\t"
   : "=r" (addr) : : "cc");

  return addr;
}

Answer 1

FreeBSD上不存在文件dl-machine.h（至少在10.1 amd64上不存在）。

在FreeBSD上就像在Linux上一样，您可以使用dlsym获取共享对象中的符号地址。

主要区别在于FreeBSD还提供了dlfunc来获取函数的地址而没有编译器警告。

Answer 2

您可以使用dladdr()获取共享对象的基址，并在对象的其他位置给定地址。如果您从共享对象的代码中调用该函数非常简单。

FreeBSD运行时加载共享对象的地址

2 个答案: