> Date: Mon, 22 Feb 2010 13:06:31 -0800 > From: "H.J. Lu" > > On Mon, Feb 22, 2010 at 11:50 AM, Mark Kettenis wrote: > >> Date: Mon, 22 Feb 2010 12:03:03 -0500 > >> From: Daniel Jacobowitz > >> > >> 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; I fear that's rather fragile. I mean, the actual value of __USER_CS/__USER32_CS is just an implementation detail isn't it?