cmake doesn't probe for CHERIOT_{LLVM_BIN,RTOS_SDK} env vars?

[nwf]

Despite the instructions saying that we need to run

sonata-system/doc/guide/building-examples.md

Lines 62 to 63 in 0e024fd

	export CHERIOT_LLVM_BIN=/path/to/cheriot-llvm/bin
	export CHERIOT_RTOS_SDK=/path/to/cheriot-rtos/sdk

the key occurrences of those strings in the cmake files herein are...

• sonata-system/sw/cheri/cheriot_toolchain.cmake

  Line 5 in 0e024fd

  if (DEFINED CHERIOT_LLVM_BIN)

  and

• sonata-system/sw/cheri/CMakeLists.txt

  Line 13 in 0e024fd

  if(NOT DEFINED CHERIOT_RTOS_SDK)

I am just a caveman and cmake frightens and confuses me, but cmake's documentation suggests that one needs to use DEFINED ENV{...} to probe at environment variables. Assuming one also wants to support the use of -D on the command line for these parameters, I think that means something like this diff should be applied:

diff --git a/sw/cheri/CMakeLists.txt b/sw/cheri/CMakeLists.txt
index f46fc99..f17ab2e 100644
--- a/sw/cheri/CMakeLists.txt
+++ b/sw/cheri/CMakeLists.txt
@@ -11,8 +11,12 @@ if(NOT DEFINED CMAKE_TOOLCHAIN_FILE)
 endif()
 
 if(NOT DEFINED CHERIOT_RTOS_SDK)
-  FetchContent_Populate(CHERIOT_RTOS)
-  set(CHERIOT_RTOS_SDK "${cheriot_rtos_SOURCE_DIR}/sdk")
+  if (NOT DEFINED ENV{CHERIOT_RTOS_SDK})
+    FetchContent_Populate(CHERIOT_RTOS)
+    set(CHERIOT_RTOS_SDK "${cheriot_rtos_SOURCE_DIR}/sdk")
+  else()
+    set(CHERIOT_RTOS_SDK "$ENV{CHERIOT_RTOS_SDK}")
+  endif()
 endif()
 
 project(sonata_system_cheriot_sw LANGUAGES C CXX ASM)
diff --git a/sw/cheri/cheriot_toolchain.cmake b/sw/cheri/cheriot_toolchain.cmake
index 0c3d690..867b1b6 100644
--- a/sw/cheri/cheriot_toolchain.cmake
+++ b/sw/cheri/cheriot_toolchain.cmake
@@ -6,6 +6,10 @@ if (DEFINED CHERIOT_LLVM_BIN)
   set(CMAKE_CXX_COMPILER "${CHERIOT_LLVM_BIN}/clang++")
   set(CMAKE_C_COMPILER   "${CHERIOT_LLVM_BIN}/clang")
   set(CMAKE_ASM_COMPILER "${CHERIOT_LLVM_BIN}/clang")
+elseif (DEFINED ENV{CHERIOT_LLVM_BIN})
+  set(CMAKE_CXX_COMPILER "$ENV{CHERIOT_LLVM_BIN}/clang++")
+  set(CMAKE_C_COMPILER   "$ENV{CHERIOT_LLVM_BIN}/clang")
+  set(CMAKE_ASM_COMPILER "$ENV{CHERIOT_LLVM_BIN}/clang")
 else()
   set(CMAKE_CXX_COMPILER clang++)
   set(CMAKE_C_COMPILER   clang)

I haven't made a PR, tho', because it's possible I'm completely off the mark.

P.S. This is also masking an annoyance that I presume will go away in time: until at least lowRISC/cheriot-rtos@02ed83a is merged to mainline, the instructions at

sonata-system/doc/guide/building-examples.md

Lines 45 to 56 in 0e024fd

	#### CHERIoT RTOS SDK Installation
	You will need a copy of [CHERIoT RTOS](https://github.com/microsoft/cheriot-rtos/tree/main) for this section.
	On Windows you may need to set `git config --global core.symlinks true` *before* cloning the repository.
	Clone the repository somewhere, *not* into the root of the `sonata-system` directory, but at the same level as `sonata-system`:
	```sh
	cd ..
	git clone --recurse https://github.com/microsoft/cheriot-rtos.git
	```

should tell us to use the lowRISC fork's sonata branch, yeah?

[marnovandermaas]

For the documentation part, here's a fix: #103
Thanks for suggesting the cmake changes.

[marnovandermaas]

This should now be fixed.