Subject: Re: [PATCH v5 4/5] powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32

From: "Jason A. Donenfeld" <[email-masked]>
Date: Thu, 5 Sep 2024 19:03:34 +0200

On Thu, Sep 05, 2024 at 06:55:27PM +0200, Christophe Leroy wrote:
> 
> 
> Le 05/09/2024 à 18:13, Jason A. Donenfeld a écrit :
> >> +/*
> >> + * The macro sets two stack frames, one for the caller and one for the callee
> >> + * because there are no requirement for the caller to set a stack frame when
> >> + * calling VDSO so it may have omitted to set one, especially on PPC64
> >> + */
> >> +
> >> +.macro cvdso_call funct
> >> +  .cfi_startproc
> >> +	PPC_STLU	r1, -PPC_MIN_STKFRM(r1)
> >> +  .cfi_adjust_cfa_offset PPC_MIN_STKFRM
> >> +	mflr		r0
> >> +	PPC_STLU	r1, -PPC_MIN_STKFRM(r1)
> >> +  .cfi_adjust_cfa_offset PPC_MIN_STKFRM
> >> +	PPC_STL		r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
> >> +  .cfi_rel_offset lr, PPC_MIN_STKFRM + PPC_LR_STKOFF
> >> +	get_datapage	r8
> >> +	addi		r8, r8, VDSO_RNG_DATA_OFFSET
> >> +	bl		CFUNC(DOTSYM(\funct))
> >> +	PPC_LL		r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
> >> +	cmpwi		r3, 0
> >> +	mtlr		r0
> >> +	addi		r1, r1, 2 * PPC_MIN_STKFRM
> >> +  .cfi_restore lr
> >> +  .cfi_def_cfa_offset 0
> >> +	crclr		so
> >> +	bgelr+
> >> +	crset		so
> >> +	neg		r3, r3
> >> +	blr
> >> +  .cfi_endproc
> >> +.endm
> > 
> > You wrote in an earlier email that this worked with time namespaces, but
> > in my testing that doesn't seem to be the case.
> 
> Did I write that ? I can't remember and neither can I remember testing 
> it with time namespaces.

It's possible I confused you with someone else? Hum. Anyway...

> >  From my test harness [1]:
> > 
> > Normal single thread
> >     vdso: 25000000 times in 12.494133131 seconds
> >     libc: 25000000 times in 69.594625188 seconds
> > syscall: 25000000 times in 67.349243972 seconds
> > Time namespace single thread
> >     vdso: 25000000 times in 71.673057436 seconds
> >     libc: 25000000 times in 71.712774121 seconds
> > syscall: 25000000 times in 66.902318080 seconds
> > 
> > I'm seeing this on ppc, ppc64, and ppc64le.
> 
> What is the command to use to test with time namespace ?

Look at the C in the commit I linked.