TLS on ARM and MIPS

[Kristof Provost]

On 2012-04-04 22:00:57 (-0700), Jason Evans <jasone at canonware.com> wrote:
> On Apr 3, 2012, at 5:41 PM, Oleksandr Tymoshenko wrote:
> > I tested it for MIPS - works fine. Unfortunately I don't have
> > ARM hardware that works with HEAD so can't test ARM part of the change.
> 
> Thanks for testing MIPS.  I'm going to just assume that TLS works everywhere.  
> If it doesn't, we'll find out soon enough. =)
> 
It appears to be rather broken on ARM, at least in combination with
shared libraries.

I'm trying to run on an OpenRD board (Kirkwood ARM core) and I see
alignment faults whenever TLS is used. Considering that malloc appears
to use it that'd be pretty much everywhere.

A minimal test case is to have a shared library expose a __thread
variable and then to write to it from outside the library.

The assembly looks like this:
int main(int argc, char **argv)
{
    8774:       e52de004        push    {lr}            ; (str lr, [sp,
#-4]!)
  kp_int = 4;
    8778:       e59f3014        ldr     r3, [pc, #20]   ; 8794
<main+0x20>
    877c:       e79f3003        ldr     r3, [pc, r3]
    8780:       ebffff4c        bl      84b8 <_init+0x58>
    8784:       e3a02004        mov     r2, #4  ; 0x4
    8788:       e7802003        str     r2, [r0, r3]

  return 0;
}

The faulting instruction is 0x8788. At that point r0 is 0x20036000, r3
is 0xffff1fff.

Let me know if you need to know anything else.
In the mean time I'll keep trying to figure out how it's supposed to be
working in the first place :)

Regards.
Kristof