> Date: Sun, 17 Sep 2023 12:40:29 +0200
> From: "Peter J. Philipp" <p...@delphinusdns.org>
Sorry Peter,
But this doesn't make any sense to me. Your C code is just as
unreadable as the assembly code ;)
And your explanation doesn't make sense. The code works fine on
existing hardware supported by OpenBSD. Your previous mails were also
high on speculation and low on facts.
Cheers,
Mark
> Hi OpenBSD/riscv64'ers!
>
> After a week of debugging a different issue I noticed this issue with the
> L2 cache in locore.S:
>
> The physical address of the base boot memory is held in register s9,
> and this is shifted by the L2 cache code by 21 to the right. In order to
> make 2 MiB offsets. However, I have found in my research that the algorithm
> is flawed a little. It expects pages not an address on s9. I wrote this
> program to understand the algorithm better. And I wrote it in C and it should
> be an exact duplication of the asm code. Please point out if it isn't.
>
> Here is the output. I'm attaching the program after this it's colour coded
> so you can see it better. As you can see with the first output there is
> bits in the PTE beyond PPN[1] in PPN[2], in the L2 cache. In the second
> output which ends at the same address the bits are perfectly aligned in
> PPN[1].
>
> pjp@polarstern$ ./l2shit | tail
> sd 1FB80003(000000000000000000000000011111101110000000000000000011) to 1014FB0
> sd 1FC00003(000000000000000000000000011111110000000000000000000011) to 1014FB8
> sd 1FC80003(000000000000000000000000011111110010000000000000000011) to 1014FC0
> sd 1FD00003(000000000000000000000000011111110100000000000000000011) to 1014FC8
> sd 1FD80003(000000000000000000000000011111110110000000000000000011) to 1014FD0
> sd 1FE00003(000000000000000000000000011111111000000000000000000011) to 1014FD8
> sd 1FE80003(000000000000000000000000011111111010000000000000000011) to 1014FE0
> sd 1FF00003(000000000000000000000000011111111100000000000000000011) to 1014FE8
> sd 1FF80003(000000000000000000000000011111111110000000000000000011) to 1014FF0
> sd 20000003(000000000000000000000000100000000000000000000000000011) to 1014FF8
> pjp@polarstern$ ./l2shit pages | tail
> sd 0FB00003(000000000000000000000000001111101100000000000000000011) to 1014FB0
> sd 0FB80003(000000000000000000000000001111101110000000000000000011) to 1014FB8
> sd 0FC00003(000000000000000000000000001111110000000000000000000011) to 1014FC0
> sd 0FC80003(000000000000000000000000001111110010000000000000000011) to 1014FC8
> sd 0FD00003(000000000000000000000000001111110100000000000000000011) to 1014FD0
> sd 0FD80003(000000000000000000000000001111110110000000000000000011) to 1014FD8
> sd 0FE00003(000000000000000000000000001111111000000000000000000011) to 1014FE0
> sd 0FE80003(000000000000000000000000001111111010000000000000000011) to 1014FE8
> sd 0FF00003(000000000000000000000000001111111100000000000000000011) to 1014FF0
> sd 0FF80003(000000000000000000000000001111111110000000000000000011) to 1014FF8
>
>
> /*
>
> 94 lla s1, pagetable_l2
> 95 srli t4, s9, L2_SHIFT
> 96 li t2, 512
> 97 add t3, t4, t2
> 98 li t0, (PTE_KERN | PTE_X)
> 99 1:
> 100 slli t2, t4, PTE_PPN1_S
> 101 or t5, t0, t2
> 102 sd t5, (s1)
> 103 addi s1, s1, PTE_SIZE
> 104
> 105 addi t4, t4, 1
> 106 bltu t4, t3, 1b
> 107
>
> */
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>
> #define P_KERN 0x1 /* not real */
> #define P_X 0x2 /* not real */
>
> char *
> binary(ulong t5)
> {
> static char ret[1280];
> int i = 0;
>
> ret[0] = '\0';
>
> for (i = 53; i >= 0; i--) {
> switch (i) {
> case (53 - 26):
> strlcat(ret,"[32m", sizeof(ret));
> break;
> case (53 - 26 - 9):
> strlcat(ret,"[34m", sizeof(ret));
> break;
> case (53 - 26 - 9 - 9):
> strlcat(ret,"[35m", sizeof(ret));
> break;
> default:
> //strlcat(ret,"[0m", sizeof(ret));
> break;
> }
>
> if (t5 & (1UL << i)) {
> strlcat(ret, "1", sizeof(ret));
> } else {
> strlcat(ret, "0", sizeof(ret));
> }
> }
>
> return (&ret[0]);
> }
>
>
>
> int
> main(int argc, char *argv[])
> {
> u_long s1 = 0x1014000; /* pagetable l2 */
> u_long s9 = 0x40200000 >> ((argc > 1) ? 12 : 0); /* physmem s9
> (pages?) */
> u_long t4 = s9 >> 21;
> u_long t2 = 512;
> u_long t3 = t4 + t2;
> u_long t0 = (P_KERN | P_X);
> u_long t5;
>
> repeat:
> t2 = t4 << 19;
> t5 = t0 | t2;
>
> printf("sd %08lX(%s[0m) to %lX\n", t5, binary(t5), s1);
>
> s1 += 8;
> t4 += 1;
>
> if (t4 < t3)
> goto repeat;
>
>
> return 0;
> }
>
> Please look at this document section 4.4.1 figure 4.21 to see the structure
> of the PTE.
>
> https://mainrechner.de/riscv-privileged-20211203.pdf
>
> Best Regards,
> -peter
>
> --
> Over thirty years experience on Unix-like Operating Systems starting with QNX.
>
>
