[U-Boot] [PATCH] - add dns

[Robin Getz]

On Sat 18 Jul 2009 21:15, Mike Frysinger pondered:
> On Saturday 18 July 2009 20:27:00 Robin Getz wrote:
> > On Sat 18 Jul 2009 18:11, Mike Frysinger pondered:
> > > keep the modulus something with only 1 bit set so gcc will optimize into
> > > a simple and operation.  probably add a comment about it too:
> > > 	/* make src port a little random, but use something trivial to compute
> > > */
> >
> > OK - So, this would give three different variations:
> >

So, these are definitality ugly...

> > net/tftp.c:     TftpOurPort = 1024 + (get_timer(0) % 3072);

00000000 <_random_port>:
   0:   78 05           [--SP] = (R7:7);
   2:   67 01           [--SP] = RETS;
   4:   a6 6f           SP += -0xc;             /* (-12) */
   6:   00 60           R0 = 0x0 (X);           /*              R0=0x0(  0) */
   8:   ff e3 fc ff     CALL 0x0 <_random_port>;
                        a: R_BFIN_PCREL24       _get_timer
   c:   41 e1 aa aa     R1.H = 0xaaaa;          /* (-21846)     R1=0xaaaa000c(-1431699444) */
  10:   01 e1 ab aa     R1.L = 0xaaab;          /* (-21845)     R1=0xaaaaaaab(-1431655765) */
  14:   38 30           R7 = R0;
  16:   ff e3 f5 ff     CALL 0x0 <_random_port>;
                        18: R_BFIN_PCREL24      ___umulsi3_highpart
  1a:   58 4e           R0 >>= 0xb;
  1c:   21 e1 00 0c     R1 = 0xc00 (X);         /*              R1=0xc00(3072) */
  20:   c8 40           R0 *= R1;
  22:   66 6c           SP += 0xc;              /* ( 12) */
  24:   c7 53           R7 = R7 - R0;
  26:   20 e1 00 04     R0 = 0x400 (X);         /*              R0=0x400(1024) */
  2a:   c7 51           R7 = R7 + R0;
  2c:   27 01           RETS = [SP++];
  2e:   07 30           R0 = R7;
  30:   38 05           (R7:7) = [SP++];
  32:   10 00           RTS;
Disassembly of section .text.NetSetTimeout:

> > net/nfs.c:      NfsOurPort = 4096 + (get_ticks() % 3072);

00000000 <_random_port>:
   0:   67 01           [--SP] = RETS;
   2:   86 6f           SP += -0x10;            /* (-16) */
   4:   ff e3 fe ff     CALL 0x0 <_random_port>;
                        6: R_BFIN_PCREL24       _get_ticks
   8:   02 60           R2 = 0x0 (X);           /*              R2=0x0(  0) */
   a:   f2 b0           [SP + 0xc] = R2;
   c:   22 e1 00 0c     R2 = 0xc00 (X);         /*              R2=0xc00(3072) */
  10:   ff e3 f8 ff     CALL 0x0 <_random_port>;
                        12: R_BFIN_PCREL24      ___umoddi3
  14:   86 6c           SP += 0x10;             /* ( 16) */
  16:   08 30           R1 = R0;
  18:   27 01           RETS = [SP++];
  1a:   20 e1 00 10     R0 = 0x1000 (X);                /*              R0=0x1000(4096) */
  1e:   01 50           R0 = R1 + R0;
  20:   10 00           RTS;


> > net/sntp.c:     SntpOurPort = 10000 + (get_timer(0) % 4096);

00000000 <_random_port>:
   0:   67 01           [--SP] = RETS;
   2:   a6 6f           SP += -0xc;             /* (-12) */
   4:   00 60           R0 = 0x0 (X);           /*              R0=0x0(  0) */
   6:   ff e3 fd ff     CALL 0x0 <_random_port>;
                        8: R_BFIN_PCREL24       _get_timer
   a:   21 e1 ff 0f     R1 = 0xfff (X);         /*              R1=0xfff(4095) */
   e:   66 6c           SP += 0xc;              /* ( 12) */
  10:   08 54           R0 = R0 & R1;
  12:   27 01           RETS = [SP++];
  14:   21 e1 10 27     R1 = 0x2710 (X);                /*              R1=0x2710(10000) */
  18:   08 50           R0 = R0 + R1;
  1a:   10 00           RTS;
Disassembly of section .text.NetSetTimeout:

> 1024 + (get_timer(0) % 0x8000);

00000000 <_random_port>:
   0:   67 01           [--SP] = RETS;
   2:   a6 6f           SP += -0xc;             /* (-12) */
   4:   00 60           R0 = 0x0 (X);           /*              R0=0x0(  0) */
   6:   ff e3 fd ff     CALL 0x0 <_random_port>;
                        8: R_BFIN_PCREL24       _get_timer
   a:   21 e1 ff 7f     R1 = 0x7fff (X);                /*              R1=0x7fff(32767) */
   e:   66 6c           SP += 0xc;              /* ( 12) */
  10:   08 54           R0 = R0 & R1;
  12:   27 01           RETS = [SP++];
  14:   21 e1 00 04     R1 = 0x400 (X);         /*              R1=0x400(1024) */
  18:   08 50           R0 = R0 + R1;
  1a:   10 00           RTS;
Disassembly of section .text.NetSetTimeout:

> > Does it make sense to have 4 different ones? (not to me)...
> >
> > Or something new & common in ./net.c:random_port()
> 
> i would make a new patch that adds a new random_port() function and converts 
> existing consumers to that, and then have the dns code rely on that.
>
> and you should adopt my implementation because the generated code is 
> much much nicer than the others ;)

At least on Blackfin - the sntp version and yours are computationally
equal - although I think yours ends up being more random - so yeah, I'll
use that one.

> a quick google shows:
>  - sntp - any non-zero source port is OK
>  - tftp - "between 0 and 65535"
>  - nfs - couldnt find anything, but i'm pretty sure there isnt one
> 
> get_ticks() and get_timer(0) are pretty much equivalent

Sounds great.