MMU Support for RISCV Arch

[akifejaz]

Describe the bug

I've tried to enable CONFIG_MMU for my qemu_riscv64 board, but build fails giving some linker stage error related to undefine z_mapped_start & arch_mem_map symbols.

west build -p always -b qemu_riscv64 samples/hello_world

To Reproduce

Steps to reproduce the behavior:

1. git checkout afce532
2. add CONFIG_MMU=y in prj.conf
3. west build -p always -b qemu_riscv64 samples/hello_world

Is there no MMU Support for RISCV arch till now? Because I find out this article it doesn't mention about MMU (memory management Unit) related anything ??
https://docs.zephyrproject.org/latest/hardware/arch/risc-v.html

Please help me in this regard, like if its enabled is there anything else I've to configured.
Best,
Akif

[fkokosinski]

Hi,

I can't seem to reproduce the exact error you've attached using the instructions you've provided, but

Is there no MMU Support for RISCV arch

That's correct, Zepyr's RISC-V port, as of date, doesn't support MMU.

If you try to build Zephyr for RISC-V with MMU support enabled, you should see a warning message about unsatisfied Kconfig dependencies:

% west build -p always -b qemu_riscv64 samples/hello_world -- -DCONFIG_MMU=y
[...]
warning: MMU (defined at kernel/Kconfig.vm:101) was assigned the value 'y' but got the value 'n'.
Check these unsatisfied dependencies: CPU_HAS_MMU (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_MMU and/or look up MMU in the
menuconfig/guiconfig interface. The Application Development Primer, Setting Configuration Values,
and Kconfig - Tips and Best Practices sections of the manual might be helpful too.

[akifejaz]

I can't seem to reproduce the exact error you've attached using the instructions you've provided, but

Hi @fkokosinski Thanks for response, yeah I forgot to mention I also enabled an internal flag CPU_HAS_MMU from arch/Kconfig

Changes:

diff --git a/samples/hello_world/prj.conf b/samples/hello_world/prj.conf
index b2a4ba59104..3dec296304f 100644
--- a/samples/hello_world/prj.conf
+++ b/samples/hello_world/prj.conf
@@ -1 +1 @@
-# nothing here
+CONFIG_MMU=y
t_aejaz@ip<>:~/Zephyr/zephyrproject/zephyr$ git diff arch/Kconfig
diff --git a/arch/Kconfig b/arch/Kconfig
index 355a6247af3..7bb338d7763 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -783,6 +783,7 @@ config CPU_HAS_MPU

 config CPU_HAS_MMU
        bool
+       default y
        help
          This hidden option is selected when the CPU has a Memory Management Unit
          (MMU).

Full Build Logs:

t_aejaz@ip-172-32-3-31:~/Zephyr/zephyrproject/zephyr$ west build -p always -b qemu_riscv64 samples/hello_world
-- west build: making build dir /home/t_aejaz/Zephyr/zephyrproject/zephyr/build pristine
-- west build: generating a build system
ZEPHYR_BASE is set to: /home/t_aejaz/Zephyr/zephyrproject/zephyr
Loading Zephyr default modules (Zephyr base).
-- Application: /home/t_aejaz/Zephyr/zephyrproject/zephyr/samples/hello_world
-- CMake version: 3.30.2
-- Found Python3: /home/t_aejaz/Zephyr/zephyrproject/.venv/bin/python3 (found suitable version "3.10.12", minimum required is "3.10") found components: Interpre
ter
-- Cache files will be written to: /home/t_aejaz/.cache/zephyr
-- Zephyr version: 4.0.0-rc1 (/home/t_aejaz/Zephyr/zephyrproject/zephyr)
-- Found west (found suitable version "1.3.0", minimum required is "0.14.0")
-- Board: qemu_riscv64, qualifiers: qemu_virt_riscv64
-- ZEPHYR_TOOLCHAIN_VARIANT not set, trying to locate Zephyr SDK
-- Found host-tools: zephyr 0.16.8 (/home/t_aejaz/Zephyr/zephyr-sdk-0.16.8)
-- Found toolchain: zephyr 0.16.8 (/home/t_aejaz/Zephyr/zephyr-sdk-0.16.8)
-- Found Dtc: /home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/sysroots/x86_64-pokysdk-linux/usr/bin/dtc (found suitable version "1.6.0", minimum required is "1.4.6")
-- Found BOARD.dts: /home/t_aejaz/Zephyr/zephyrproject/zephyr/boards/qemu/riscv64/qemu_riscv64.dts
-- Generated zephyr.dts: /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/zephyr.dts
-- Generated pickled edt: /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/edt.pickle
-- Generated zephyr.dts: /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/zephyr.dts
-- Generated devicetree_generated.h: /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/include/generated/zephyr/devicetree_generated.h
-- Including generated dts.cmake file: /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/dts.cmake
Parsing /home/t_aejaz/Zephyr/zephyrproject/zephyr/Kconfig
Loaded configuration '/home/t_aejaz/Zephyr/zephyrproject/zephyr/boards/qemu/riscv64/qemu_riscv64_defconfig'
Merged configuration '/home/t_aejaz/Zephyr/zephyrproject/zephyr/samples/hello_world/prj.conf'
Configuration saved to '/home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/.config'
Kconfig header saved to '/home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/include/generated/zephyr/autoconf.h'
-- Found GnuLd: /home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/riscv64-zephyr-elf/riscv64-zephyr-elf/bin/ld.bfd (found version "2.38")
-- The C compiler identification is GNU 12.2.0
-- The CXX compiler identification is GNU 12.2.0
-- The ASM compiler identification is GNU
-- Found assembler: /home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/riscv64-zephyr-elf/bin/riscv64-zephyr-elf-gcc
Zephyr package found at: /home/t_aejaz/Zephyr/zephyrproject/zephyr/share/zephyr-package/cmake
-- Configuring done (6.5s)
-- Generating done (0.1s)
-- Build files have been written to: /home/t_aejaz/Zephyr/zephyrproject/zephyr/build
-- west build: building application
[1/103] Preparing syscall dependency handling

[2/103] Generating include/generated/zephyr/version.h
-- Zephyr version: 4.0.0-rc1 (/home/t_aejaz/Zephyr/zephyrproject/zephyr), build: v4.0.0-rc1-10-gafce5329f772
[98/103] Linking C executable zephyr/zephyr_pre0.elf
FAILED: zephyr/zephyr_pre0.elf zephyr/zephyr_pre0.map /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/zephyr_pre0.map
: && ccache /home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/riscv64-zephyr-elf/bin/riscv64-zephyr-elf-gcc  -gdwarf-4 -gdwarf-4 zephyr/CMakeFiles/zephyr_pre0.dir/misc/empty_file.c.obj -o zephyr/zephyr_pre0.elf  zephyr/CMakeFiles/offsets.dir/./arch/riscv/core/offsets/offsets.c.obj  -T  zephyr/linker_zephyr_pre0.cmd  -Wl,-Map=/home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr/zephyr_pre0.map  -Wl,--whole-archive  app/libapp.a  zephyr/libzephyr.a  zephyr/arch/common/libarch__common.a  zephyr/arch/arch/riscv/core/libarch__riscv__core.a  zephyr/lib/libc/picolibc/liblib__libc__picolibc.a  zephyr/lib/libc/common/liblib__libc__common.a  zephyr/drivers/interrupt_controller/libdrivers__interrupt_controller.a  zephyr/drivers/console/libdrivers__console.a  zephyr/drivers/serial/libdrivers__serial.a  zephyr/drivers/timer/libdrivers__timer.a  -Wl,--no-whole-archive  zephyr/kernel/libkernel.a  -L/home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr  zephyr/arch/common/libisr_tables.a  -mcmodel=medany  -mabi=lp64  -march=rv64imac_zicsr_zifencei  -fuse-ld=bfd  -Wl,--gc-sections  -Wl,--build-id=none  -Wl,--sort-common=descending  -Wl,--sort-section=alignment  -Wl,-u,_OffsetAbsSyms  -Wl,-u,_ConfigAbsSyms  -nostdlib  -static  -Wl,-X  -Wl,-N  -Wl,--orphan-handling=warn  -Wl,-no-pie  -specs=picolibc.specs  -DPICOLIBC_LONG_LONG_PRINTF_SCANF -L"/home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/riscv64-zephyr-elf/bin/../lib/gcc/riscv64-zephyr-elf/12.2.0/rv64imac_zicsr_zifencei/lp64/medany" -lc -lgcc && cd /home/t_aejaz/Zephyr/zephyrproject/zephyr/build/zephyr && /usr/bin/cmake -E true
/home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/riscv64-zephyr-elf/bin/../lib/gcc/riscv64-zephyr-elf/12.2.0/../../../../riscv64-zephyr-elf/bin/ld.bfd: zephyr/kernel/libkernel.a(mmu.c.obj): in function `k_mem_map_phys_bare':
/home/t_aejaz/Zephyr/zephyrproject/zephyr/kernel/mmu.c:976: undefined reference to `arch_mem_map'
/home/t_aejaz/Zephyr/zephyr-sdk-0.16.8/riscv64-zephyr-elf/bin/../lib/gcc/riscv64-zephyr-elf/12.2.0/../../../../riscv64-zephyr-elf/bin/ld.bfd: zephyr/kernel/libkernel.a(mmu.c.obj): in function `z_mem_manage_init':
/home/t_aejaz/Zephyr/zephyrproject/zephyr/kernel/mmu.c:1103: undefined reference to `z_mapped_start'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: /usr/bin/cmake --build /home/t_aejaz/Zephyr/zephyrproject/zephyr/build

[kgingerale]

Hey!
My group chose to try and work on this issue as part of our grade for our masters class. We have the baseline code written for sv32 and are working on testing it now. However, we have run into a situation where PTE permission flags are not being enforced, even when the thread is in user mode (also tried not having user mode/threads setup, just in a basic main.c). Has anyone seen something similar, or is there a quirk with QEMU’s RISC-V MMU emulation?