ok deraadt Christian Weisgerber <na...@mips.inka.de> wrote:
> Mark Kettenis: > > > > Here is a cpu_rnd_messybits() implementation for arm64. > > > It reads the virtual counter and xors it with a bit-reversed copy > > > of itself. > > > > > > The virtual counter is used by the only timecounter implementation > > > used on arm64, so I assume it is generally available. > > > > > > It's a 64-bit counter, which we reduce to 32 bits. Since there is > > > progressively less entropy in the higher bits of a counter than in > > > the lower bits, it intuitively makes sense not just to do hi^lo, > > > but to bit-reverse one half in order to extract maximal entropy, > > > and on aarch64 bit reversal is a simple instruction. > > > > Can you make that uint64_t? > > Can you use %0 and %1 instead of %x0 and %x1? > > Right. > > Index: arch/arm64/arm64/machdep.c > =================================================================== > RCS file: /cvs/src/sys/arch/arm64/arm64/machdep.c,v > retrieving revision 1.52 > diff -u -p -r1.52 machdep.c > --- arch/arm64/arm64/machdep.c 31 May 2020 06:23:57 -0000 1.52 > +++ arch/arm64/arm64/machdep.c 5 Jun 2020 20:00:20 -0000 > @@ -1247,12 +1247,3 @@ dumpregs(struct trapframe *frame) > printf("pc: 0x%016lx\n", frame->tf_elr); > printf("spsr: 0x%016lx\n", frame->tf_spsr); > } > - > -unsigned int > -cpu_rnd_messybits(void) > -{ > - struct timespec ts; > - > - nanotime(&ts); > - return (ts.tv_nsec ^ (ts.tv_sec << 20)); > -} > Index: arch/arm64/include/cpu.h > =================================================================== > RCS file: /cvs/src/sys/arch/arm64/include/cpu.h,v > retrieving revision 1.17 > diff -u -p -r1.17 cpu.h > --- arch/arm64/include/cpu.h 31 May 2020 06:23:57 -0000 1.17 > +++ arch/arm64/include/cpu.h 5 Jun 2020 22:13:07 -0000 > @@ -183,7 +183,16 @@ void cpu_boot_secondary_processors(void) > > #define curpcb curcpu()->ci_curpcb > > -unsigned int cpu_rnd_messybits(void); > +static inline unsigned int > +cpu_rnd_messybits(void) > +{ > + uint64_t val, rval; > + > + __asm volatile("mrs %0, CNTVCT_EL0; rbit %1, %0;" > + : "=r" (val), "=r" (rval)); > + > + return (val ^ rval); > +} > > /* > * Scheduling glue > -- > Christian "naddy" Weisgerber na...@mips.inka.de >