Add an option to disable QEMU testing

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.

Author: dcandler

CMakeLists.txt

@@ -150,6 +150,11 @@ option(
     "During checkout, apply optional downstream patches to
     llvm-project to improve performance."
 )
+option(
+    ENABLE_QEMU_TESTING
+    "Tests using QEMU are enabled by default, but can be disabled."
+    ON
+)
 option(
     ENABLE_FVP_TESTING
     "Tests using FVP need to be explictly enabled."
@@ -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

@@ -33,6 +33,11 @@ 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
+    "Tests using QEMU are enabled by default, but can be disabled."
+    ON
+)
 option(
     ENABLE_FVP_TESTING
     "Tests using FVP need to be explictly enabled."
@@ -163,7 +168,7 @@ foreach(lib_idx RANGE ${lib_count_dec})
 
             # FVP testing should default to off, so override any 
             # settings from the JSON.
-            if(test_executor STREQUAL "fvp" AND NOT ${ENABLE_FVP_TESTING})
+            if((test_executor STREQUAL "qemu" AND NOT ${ENABLE_QEMU_TESTING}) OR (test_executor STREQUAL "fvp" AND NOT ${ENABLE_FVP_TESTING}))
                 set(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.