Ruby C 扩展 - 64 位指针被截断导致段错误

发布于 2024-12-02 21:17:04 字数 1102 浏览 1 评论 0原文

我正在尝试使用 c 语言编写 ruby 扩展，在 Mac OSX 上使用 ruby 1.9.2。我不断收到由函数返回的 64 位指针被截断为 32 位值并尝试访问低内存引起的段错误。

这就是我的想法。 VALUE 是一个 long，在 ruby 源代码中定义，除非 sizeof(long) 为 8 个字节，否则代码将无法编译。

在 file_b.c 中：

VALUE
rb_helper_function_foo(VALUE file)
{
  VALUE blah;

  ...

  //Using gdb, blah right here is a 64bit address, ex: 0x1 009d 62a0
  return blah;
}

在 file_a.c 中

VALUE
func_do_stuff(int argc, VALUE *argv, VALUE obj)
{
  VALUE filename, file_path;

  ...

  // But here, the size of what is returned is 4 bytes
  // file_path has a size of 8 bytes though
  file_path = rb_helper_function_foo(filename);

  //This statement will segfault :-(
  if(!RTEST(file_path))
  {
    ...
  }
  ...
}

在函数调用结束时，返回值具有正确的地址，但仅返回低 4 个字节：0x009d52a0 而不是 0x1009d52a0。访问低内存地址会导致段错误。

在返回期间调用的汇编代码中，有一条指令

movslq %eax, %r12

仅复制较低的 4 个字节，但我需要复制 %rax 的所有 8 个字节。

我使用的是 ruby 1.9.2-p290（尽管它与 p180 相同），Mac OSX 10.6.8，使用 xcode 4.0.1（带有 gcc 4.2.1），但我也尝试升级到 gcc 4.6.1。之前也尝试过xcode 3.2。

感谢您能给我的任何帮助。

原文

I'm working on trying to get a ruby extension written in c, working with ruby 1.9.2 on Mac OSX. I keep getting a segfault caused by a 64-bit pointer returned from a function being truncated to a 32-bit value and trying to access low memory.

Here's what I've figured out about it. VALUE is a long, defined in the ruby source code, and the code won't compile unless sizeof(long) is 8 bytes.

In file_b.c:

VALUE
rb_helper_function_foo(VALUE file)
{
  VALUE blah;

  ...

  //Using gdb, blah right here is a 64bit address, ex: 0x1 009d 62a0
  return blah;
}

In file_a.c

VALUE
func_do_stuff(int argc, VALUE *argv, VALUE obj)
{
  VALUE filename, file_path;

  ...

  // But here, the size of what is returned is 4 bytes
  // file_path has a size of 8 bytes though
  file_path = rb_helper_function_foo(filename);

  //This statement will segfault :-(
  if(!RTEST(file_path))
  {
    ...
  }
  ...
}

At the end of the function call, the return value has the correct address, but only the lower 4 bytes get returned: 0x009d52a0 instead of 0x1009d52a0. Accessing the low memory address is causing a segfault.

In the assembly code that gets called during the return, there's this instruction

movslq %eax, %r12

which only copies the lower 4 bytes, but I need all 8 bytes of %rax to be copied.

I'm on ruby 1.9.2-p290 (though it did the same with p180), Mac OSX 10.6.8, using xcode 4.0.1 (with gcc 4.2.1), but I also tried upgrading to gcc 4.6.1. It has also previously tried xcode 3.2.

Thanks for any help you can give me.

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