platforms: add RPi4 32-bit build

[axel-h]

See seL4/seL4#976

Is there anything else we would need for CI testing?

[Ivan-Velickovic]

Someone needs to resolve seL4/util_libs#171 first.

[Ivan-Velickovic]

The RPi4 port seems to have been broken for a long time, I fixed most of the issues but seL4/util_libs#171 is still outstanding.

[JDuchniewicz]

In seL4/sel4test#150 I fixed the issues with serial driver for Rpi4 in sel4test.

[lsf37]

Are these not two different issues? This one here was for 32 bit, the one Jakub fixed was for release mode/uart.

[JDuchniewicz]

Maybe I am confused but @Ivan-Velickovic mentioned the issue I fixed in the PR: seL4/sel4test#150, specifically seL4/util_libs#171

[lsf37]

He did, but I think Ivan's original comment was already potentially confused. I guess the main question is: have you tried running the RPI4 in 32 bit mode and does it work?

[JDuchniewicz]

Yeah just tried compiling it on the newest master and it fails with linker errors:

toolchains/arm-gnu-toolchain-14.3.rel1-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/14.3.1/../../../../arm-none-eabi/bin/ld: kernel_all.c:(.boot.text+0x6fc): undefined reference to `lockTLBEntry'

Will fix these and then confirm that the platform works.

[JDuchniewicz]

@lsf37 I confirm sel4test works for RPi4 in the 32-bit mode. Since, I build it with arm-linux-gnueabihf toolchain I had to add it to gcc.cmake in kernel and add -fno-stack-protector otherwise the loader would not link.

Same for sel4bench except I encountered an issue with running it. Reported it as seL4/sel4bench#64

[JDuchniewicz]

Works for me after adding a fix to sel4bench (for 32-bits there is just the PMCCNTR counter so we had asserts firing due PMCR reporting 0). https://arm.jonpalmisc.com/latest_sysreg/AArch32-pmcr

Anything else I should do @lsf37 ?