Add an option to disable QEMU testing (#586)

Testing with QEMU is implicitly enabled by default, but configuring the
project to run with tests requires QEMU. As testing with QEMU is
considered optional, it should be possible to disable tests when QEMU is
not available or testing is not needed.

Since there is already an option for controlling FVP testing, this patch
adds a similar option for QEMU, ENABLE_QEMU_TESTING, which instead
defaults to ON. This can then be turned off when QEMU is not installed,
so that configurations where QEMU is expected can suitably detect and
show an error when it is missing.

CMakeLists.txt

@@ -150,9 +150,14 @@ option(
     "During checkout, apply optional downstream patches to
     llvm-project to improve performance."
 )
+option(
+    ENABLE_QEMU_TESTING
+    "Enable tests that use QEMU. This option is ON by default."
+    ON
+)
 option(
     ENABLE_FVP_TESTING
-    "Tests using FVP need to be explictly enabled."
+    "Enable tests that use FVPs. This option is OFF by default."
 )
 set(
     FVP_INSTALL_DIR
@@ -596,6 +601,7 @@ if(NOT PREBUILT_TARGET_LIBRARIES)
         -DENABLE_VARIANTS=${ENABLE_VARIANTS_PASSTHROUGH}
         -DLIBC_HDRGEN=${LIBC_HDRGEN}
         -DFVP_INSTALL_DIR=${FVP_INSTALL_DIR}
+        -DENABLE_QEMU_TESTING=${ENABLE_QEMU_TESTING}
         -DENABLE_FVP_TESTING=${ENABLE_FVP_TESTING}
         -DFVP_CONFIG_DIR=${CMAKE_CURRENT_SOURCE_DIR}/fvp/config
         -DFETCHCONTENT_SOURCE_DIR_LLVMPROJECT=${FETCHCONTENT_SOURCE_DIR_LLVMPROJECT}

arm-multilib/CMakeLists.txt

@@ -33,9 +33,14 @@ set(C_LIBRARY "picolibc" CACHE STRING "Which C library to use.")
 set_property(CACHE C_LIBRARY PROPERTY STRINGS picolibc newlib llvmlibc)
 set(LLVM_BINARY_DIR "" CACHE PATH "Path to LLVM toolchain build or install root.")
 set(LIBC_HDRGEN "" CACHE PATH "Path to prebuilt lbc-hdrgen if not included in LLVM binaries set by LLVM_BINARY_DIR")
+option(
+    ENABLE_QEMU_TESTING
+    "Enable tests that use QEMU. This option is ON by default."
+    ON
+)
 option(
     ENABLE_FVP_TESTING
-    "Tests using FVP need to be explictly enabled."
+    "Enable tests that use FVPs. This option is OFF by default."
 )
 set(
     FVP_INSTALL_DIR
@@ -162,9 +167,9 @@ foreach(lib_idx RANGE ${lib_count_dec})
             file(READ ${variant_json_file} variant_json_str)
             string(JSON test_executor GET ${variant_json_str} "args" "common" "TEST_EXECUTOR")
 
-            # FVP testing should default to off, so override any 
-            # settings from the JSON.
-            if(test_executor STREQUAL "fvp" AND NOT ${ENABLE_FVP_TESTING})
+            # The multilib project can be configured to disable QEMU and/or FVP
+            # testing, which will need to override the settings from the json.
+            if((test_executor STREQUAL "qemu" AND NOT ${ENABLE_QEMU_TESTING}) OR (test_executor STREQUAL "fvp" AND NOT ${ENABLE_FVP_TESTING}))
                 list(APPEND additional_cmake_args "-DENABLE_LIBC_TESTS=OFF" "-DENABLE_COMPILER_RT_TESTS=OFF" "-DENABLE_LIBCXX_TESTS=OFF")
                 set(read_ENABLE_LIBC_TESTS "OFF")
                 set(read_ENABLE_COMPILER_RT_TESTS "OFF")

docs/building-from-source.md

@@ -36,6 +36,10 @@ $ brew install llvm python3 git make ninja qemu cmake
 $ pip install meson
 ```
 
+Testing with QEMU is enabled by default, but can be disabled using the 
+`-DENABLE_QEMU_TESTING=OFF` CMake option if testing is not required or QEMU is
+not installed.
+
 Some recent targets are not supported by QEMU, for these the Arm FVP models are
 used instead. These models are available free-of-change but are not
 open-source, and come with their own licenses.