Re: mips RDHWR instruction in glibc

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

On Thu, 15 Jun 2006 11:32:52 -0400, Daniel Jacobowitz <dan@debian.org> wrote:
> > I also found a "rdhwr" in gcc's mips.md file ("tls_get_tp_<mode>").
> > Is this the origin?  MD is a very foreign language for me...
> 
> Yes.  Compile something like this with -O2 but without -fpic:
> 
> __thread int x;
> int foo() { return x; }
> 
> It should use the IE model, which will generate a rdhwr.

Thanks.  So this must be a gcc issue, not glibc issue.

extern __thread int x;
int foo(int arg)
{
        if (arg)
                return x;
        return 0;
}

If I compiled this program with -O2 I got:

foo:
        .frame  $sp,0,$31               # vars= 0, regs= 0/0, args= 0, gp= 0
        .mask   0x00000000,0
        .fmask  0x00000000,0
        .set    noreorder
        .cpload $25
        .set    nomacro
        
        lw      $2,%gottprel(x)($28)
        .set    push
        .set    mips32r2        
        rdhwr   $3,$29
        .set    pop
        addu    $2,$2,$3
        beq     $4,$0,$L4
        move    $3,$0

        lw      $3,0($2)
$L4:
        j       $31
        move    $2,$3

It looks too bad for arg == 0 case.  I should ask on gcc list.

---
Atsushi Nemoto