Re: PATCH: Enable x86 XML target descriptions

H.J. Lu
2010-02-22T21:06:40Z

On Mon, Feb 22, 2010 at 11:50 AM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> Date: Mon, 22 Feb 2010 12:03:03 -0500
>> From: Daniel Jacobowitz <dan@codesourcery.com>
>>
>> On Mon, Feb 22, 2010 at 05:56:58PM +0100, Mark Kettenis wrote:
>> > I've looked at the Linux kernel sources for the kernel on my
>> > workstation (2.6.27 in its OpenSUSE incarnation), and the only way to
>> > distinguish between a 32-bit and a 64-bit process seems to be to
>> > attempt to write one of the debug address registers with a value
>> > that's larger than 0xffffffff.  If that fails, you have a 32-bit
>> > process, otherwise it's a 64-bit process.
>>
>> Yuck :-(  But I didn't see anything else either.
>
> Indeed.
>
>> Is there an eflags bit for this?  Even if so, IIRC, we may not want to
>> use it; it's possible to run 32-bit code in a 64-bit process and some
>> overly clever programs may do so.
>
> Nope, there is no %eflags/%rflags bit for this.  Not quite sure what
> running 32-bit code in a 64-bit process actually means.  But I'd guess
> you want the 64-bit view on the registers in that case.
>
> Anyway, I think it's probably best if HJ leaves this bit out of this
> diff for now.  We can revisit the issue when AVX support is
> introduced.
>

Please see if my latest patch is OK:

---
/* Get CS register. */
errno = 0;
cs = ptrace (PTRACE_PEEKUSER, tid,
offsetof (struct user_regs_struct, cs), 0);
if (errno != 0)
perror_with_name (_("Couldn't get CS register"));

/* Value of CS register:
1. 64bit: 0x33.
2. 32bit: 0x23.
*/
if (cs == 0x33)
return tdesc_amd64_linux;
else
return tdesc_i386_linux;
---

In kernel, there is

regs->cs = test_thread_flag(TIF_64BIT_ILP32) ? __USER_CS : __USER32_CS;

Thanks.

--
H.J.