PMPoke: Testing the PMP

Small ASM tests for the RISC-V Physical Memory Protection unit, on top of a Verilator emulator.

Installation

To build and run the different tests, a RISC-V toolchain installation is needed as well as a core Verilator emulator (Rocket or CVA6 for example):

export RISCV=/path/to/the/toolchain
export EMULATOR=/path/to/compiled/emulator

You can then build the elf/dump/core log / vcd using:

make bin/<test_name>.elf|dump|corelog|vcd

For mmode_tor2 for example:

make bin/mmode_tor2.corelog

Note: Intermediate files are deleted by make as the makefile does not explicitely state them..... I'd rather not expand the makefile and specify the needed intermediate file through make directly if needed, (e.g. make bin/mmode_tor2.elf to access the elf file, etc.). If you want to keep all intermediate files, I found that replacing % in the following snippets with the actual name will keep them (needs to be duplicated for each new test though 🥱)

bin/%.elf: $(COMS_O) $(bin_dir)/%.o
	$(RISCV_GCC) $(RISCV_LINK_OPTS) $^ -o $@

Test memory layout

The tests workflow is the following:

• main: that stores the data_region0 address in s2 and data_region1 in s3
• pmp_setup: that fills the pmpaddri and pmpcfgi registers in M-mode
• test_start: that tries to access memory (either in U-mode or M-mode)

The different data_regioni contain the same data.bin, a 256-word iteration (0x00000000, 0x00000001, ...). They are 0x100 aligned and usually end up at 0x80000d00, 0x0x80000e00, etc. (this can be checked in the dumps!)