Ensure execute_process is error checked

Check the return value from execute_process calls and fail
with an appropriate message.

This makes debugging of cmake failures much easier.

Signed-off-by: Ben Leslie <benno@brkawy.com>

config.cmake

@@ -135,14 +135,22 @@ if(DEFINED KernelDTSList AND (NOT "${KernelDTSList}" STREQUAL ""))
         execute_process(
             COMMAND
                 ${DTC_TOOL} -q -I dts -O dtb -o ${KernelDTBPath} ${KernelDTSIntermediate}
+            RESULT_VARIABLE error
         )
+        if(error)
+            message(FATAL_ERROR "Failed to compile DTS to DTB: ${KernelDTBPath}")
+        endif()
         # Track the size of the DTB for downstream tools
         execute_process(
             COMMAND
                 ${STAT_TOOL} -c '%s' ${KernelDTBPath}
             OUTPUT_VARIABLE KernelDTBSize
             OUTPUT_STRIP_TRAILING_WHITESPACE
+            RESULT_VARIABLE error
         )
+        if(error)
+            message(FATAL_ERROR "Failed to determine KernelDTBSize: ${KernelDTBPath}")
+        endif()
         string(
             REPLACE
                 "\'"

src/plat/qemu-arm-virt/config.cmake

@@ -34,7 +34,14 @@ if(KernelPlatformQEMUArmVirt)
         set(KernelArmCortexA53 ON)
         set(KernelArchArmV8a ON)
     endif()
-    execute_process(COMMAND qemu-system-${QEMU_ARCH} -version OUTPUT_VARIABLE QEMU_VERSION_STR)
+    execute_process(
+        COMMAND qemu-system-${QEMU_ARCH} -version
+        OUTPUT_VARIABLE QEMU_VERSION_STR
+        RESULT_VARIABLE error
+    )
+    if(error)
+        message(FATAL_ERROR "Failed to determine qemu version (qemu-system-${QEMU_ARCH})")
+    endif()
     string(
         REGEX
             MATCH
@@ -69,14 +76,22 @@ if(KernelPlatformQEMUArmVirt)
             ${QEMU_BINARY} -machine virt,dumpdtb=${DTBPath},${QEMU_VIRT_OPTION} -m ${QEMU_MEMORY}
             -cpu ${ARM_CPU} -smp ${QEMU_SMP_OPTION} -nographic
         ERROR_VARIABLE QEMU_OUTPUT_MESSAGE
+        RESULT_VARIABLE error
     )
     string(STRIP ${QEMU_OUTPUT_MESSAGE} QEMU_OUTPUT_MESSAGE)
     message(STATUS ${QEMU_OUTPUT_MESSAGE})
+    if(error)
+        message(FATAL_ERROR "Failed to dump DTB using ${QEMU_BINARY})")
+    endif()
     execute_process(
         COMMAND
             dtc -q -I dtb -O dts ${DTBPath}
         OUTPUT_FILE ${DTSPath}
+        RESULT_VARIABLE error
     )
+    if(error)
+        message(FATAL_ERROR "Failed to convert DTB to DTS (${DTBPath})")
+    endif()
     list(APPEND KernelDTSList "${DTSPath}")
     list(APPEND KernelDTSList "src/plat/qemu-arm-virt/overlay-qemu-arm-virt.dts")
     if(KernelArmHypervisorSupport)