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arm: start documenting paging

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Ciro Santilli 六四事件 法轮功
2019-07-18 00:00:00 +00:00
parent 2b3e6bcff1
commit 3ea041e4d9
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20
README.adoc
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@@ -15096,6 +15096,26 @@ Bibliography:
* https://stackoverflow.com/questions/51094092/how-to-make-timer-irq-work-on-qemu-machine-virt-cpu-cortex-a57
* https://stackoverflow.com/questions/44198483/arm-timers-and-interrupts
==== ARM paging
TODO create a minimal working aarch64 example analogous to the x86 one at: https://github.com/cirosantilli/x86-bare-metal-examples/blob/6dc9a73830fc05358d8d66128f740ef9906f7677/paging.S
A general introduction to paging with x86 examples can be found at: https://cirosantilli.com/x86-paging[].
ARM paging is documented at <<armarm8-db>> Chapter D5 and is mostly called VMSAv8 in the ARMv8 manual (Virtual Memory System Architecture).
Paging is enabled by the `SCTLR_EL1.M` bit.
The base table address is selected by the register documented at <<armarm8-db>> D12.2.111 "TTBR0_EL1, Translation Table Base Register 0 (EL1)".
There is also a `TTBR1_EL1` register, which is for the second translation stage to speed up virtualization: https://en.wikipedia.org/wiki/Second_Level_Address_Translation and will not be used in this section.
The translation types are described at: <<armarm8-db>> D5.2.4 "Memory translation granule size".
From this we can see that the translation scheme uses up to 4 levels (0 to 3) and has possible granule sizes 4KiB, 16KiB and 64KiB.
Page table formats are described at <<armarm8-db>> D5.3.1 "VMSAv8-64 translation table level 0, level 1, and level 2 descriptor formats".
==== ARM baremetal bibliography
First, also consider the userland bibliography: <<arm-assembly-bibliography>>.

14
baremetal/arch/aarch64/dump_regs.c
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@@ -8,11 +8,25 @@ int main(void) {
__asm__ ("mrs %0, sctlr_el1" : "=r" (sctlr_el1) : :);
printf("SCTLR_EL1 0x%" PRIX32 "\n", sctlr_el1);
printf("SCTLR_EL1.A 0x%" PRIX32 "\n", (sctlr_el1 >> 1) & 1);
/* https://cirosantilli.com/linux-kernel-module-cheat#arm-paging */
printf("SCTLR_EL1.M 0x%" PRIX32 "\n", (sctlr_el1 >> 0) & 1);
uint64_t CurrentEL;
__asm__ ("mrs %0, CurrentEL;" : "=r" (CurrentEL) : :);
printf("CurrentEL 0x%" PRIX64 "\n", CurrentEL);
/* https://cirosantilli.com/linux-kernel-module-cheat#arm-exception-levels */
printf("CurrentEL.EL 0x%" PRIX64 "\n", CurrentEL >> 2);
/* https://cirosantilli.com/linux-kernel-module-cheat#arm-paging */
{
uint64_t tcr_el1;
__asm__ ("mrs %0, tcr_el1;" : "=r" (tcr_el1) : :);
printf("TCR_EL1 0x%" PRIX64 "\n", tcr_el1);
uint64_t ttbr0_el1;
__asm__ ("mrs %0, ttbr0_el1;" : "=r" (ttbr0_el1) : :);
printf("TTBR0_EL1 0x%" PRIX64 "\n", ttbr0_el1);
}
return 0;
}