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Re: [PATCH 1/5] PowerPC: Consolidate NPTL/non versions of vfork
- From: Richard Henderson <rth at twiddle dot net>
- To: Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>, "GNU C. Library" <libc-alpha at sourceware dot org>, Roland McGrath <roland at hack dot frob dot com>
- Date: Fri, 23 May 2014 11:29:46 -0700
- Subject: Re: [PATCH 1/5] PowerPC: Consolidate NPTL/non versions of vfork
- Authentication-results: sourceware.org; auth=none
- References: <537F4C7E dot 4020005 at linux dot vnet dot ibm dot com>
On 05/23/2014 06:26 AM, Adhemerval Zanella wrote:
> + /* Load the TCB-cached PID value and negates it. If It it is zero
> + sets it to 0x800000. And then sets its value again on TCB field.
> + See raise.c for the logic that relies on this value. */
> + lwz r0,PID(r13)
> + cmpwi cr0,r0,0
> + neg r0,r0
> + bne- cr0,1f
> + lis r0,0x8000
> +1: stw r0,PID(r13)
I was thinking about this when I did the alpha port:
Why don't we use ~pid instead of -pid? That way we still get high-bit set
semantics, but don't have to special-case 0, and so don't need a branch here
(or a conditional move on other hosts)?
There is a tiny matter of updating all of the architectures all at once though...