Wrong compiler flag check result on Windows LLVM toolchain

[stephanosio]

Summary

When building Zephyr with Zephyr SDK LLVM toolchain on Windows, CMake compiler flag check function (check_compiler_flag) "randomly" returns wrong results.

Running CMake twice with the toolchain compatibility database cache cleared before each run, the compiler flag check results differ:

--- run1.log.nl	2024-10-28 01:36:58.333289400 +0000
+++ run2.log.nl	2024-10-28 01:37:04.554760200 +0000
@@ -26,20 +26,20 @@
     26	-- The ASM compiler identification is Clang with GNU-like command-line
     27	-- Found assembler: S:/llvm/bin/clang.exe
     28	-- @@ C, , 1
-    29	-- @@ C, -Wall, 1
+    29	-- @@ C, -Wall, 0
     30	-- @@ C, -Wformat;-Wformat-security, 1
-    31	-- @@ C, -Wformat;-Wformat-zero-length, 1
-    32	-- @@ C, -Wdouble-promotion, 0
+    31	-- @@ C, -Wformat;-Wformat-zero-length, 0
+    32	-- @@ C, -Wdouble-promotion, 1
     33	-- @@ C, -Wpointer-sign, 1
     34	-- @@ C, -Wpointer-arith, 0
-    35	-- @@ C, -Wexpansion-to-defined, 0
+    35	-- @@ C, -Wexpansion-to-defined, 1
     36	-- @@ C, -Wlogical-op, 0
-    37	-- @@ C, -Wmissing-field-initializers, 0
+    37	-- @@ C, -Wmissing-field-initializers, 1
     38	-- @@ C, -Wpacked-bitfield-compat, 0
-    39	-- @@ C, -Wvla, 1
+    39	-- @@ C, -Wvla, 0
     40	-- @@ C, -Wunused-but-set-variable, 0
     41	-- @@ C, -Werror=implicit-int, 1
-    42	-- @@ C, -mstack-protector-guard=global, 0
+    42	-- @@ C, -mstack-protector-guard=global, 1
     43	-- @@ C, -fno-freestanding, 0
     44	-- @@ C, -ffreestanding, 1
     45	-- @@ C, -gdwarf-4, 1
@@ -49,45 +49,45 @@
     49	-- @@ C, -Wtypedef-redefinition, 0
     50	-- @@ C, -Wdeprecated-non-prototype, 1
     51	-- @@ C, -Wold-style-definition, 1
-    52	-- @@ C, -Wmissing-prototypes, 0
-    53	-- @@ C, -Wmissing-include-dirs, 1
+    52	-- @@ C, -Wmissing-prototypes, 1
+    53	-- @@ C, -Wmissing-include-dirs, 0
     54	-- @@ C, -Wunused-but-set-variable, 0
-    55	-- @@ C, -Wmissing-field-initializers, 0
+    55	-- @@ C, -Wmissing-field-initializers, 1
     56	-- @@ C, -Wsometimes-uninitialized, 0
-    57	-- @@ C, -Wshift-overflow, 1
-    58	-- @@ C, -Wmissing-braces, 0
-    59	-- @@ C, -Wself-assign, 1
+    57	-- @@ C, -Wshift-overflow, 0
+    58	-- @@ C, -Wmissing-braces, 1
+    59	-- @@ C, -Wself-assign, 0
     60	-- @@ C, -Waddress-of-packed-member, 1
     61	-- @@ C, -Wunused-function, 1
-    62	-- @@ C, -Winitializer-overrides, 0
-    63	-- @@ C, -Wsection, 1
-    64	-- @@ C, -Wunknown-warning-option, 0
+    62	-- @@ C, -Winitializer-overrides, 1
+    63	-- @@ C, -Wsection, 0
+    64	-- @@ C, -Wunknown-warning-option, 1
     65	-- @@ C, -Wunused-variable, 1
     66	-- @@ C, -Wformat-invalid-specifier, 0
-    67	-- @@ C, -Wgnu, 0
+    67	-- @@ C, -Wgnu, 1
     68	-- @@ C, -Wtautological-compare, 0
     69	-- @@ C, , 0
-    70	-- @@ C, , 1
+    70	-- @@ C, , 0
     71	-- @@ C, , 1
     72	-- @@ C, , 1
     73	-- @@ C, , 0
-    74	-- @@ C, , 0
+    74	-- @@ C, , 1
     75	-- @@ C, , 1
     76	-- @@ C, , 0
     77	-- @@ C, , 0
     78	-- @@ C, , 1
     79	-- @@ C, , 0
     80	-- @@ C, , 1
-    81	-- @@ C, , 0
-    82	-- @@ C, , 1
+    81	-- @@ C, , 1
+    82	-- @@ C, , 0
     83	-- @@ C, -fno-asynchronous-unwind-tables, 1
-    84	-- @@ C, -ftls-model=local-exec, 1
-    85	-- @@ C, -Wvla, 1
-    86	-- @@ C, -fmacro-prefix-map=C:/a/sdk-ng/sdk-ng/zephyrproject/zephyr/samples/hello_world=CMAKE_SOURCE_DIR, 0
-    87	-- @@ C, -fmacro-prefix-map=C:/a/sdk-ng/sdk-ng/zephyrproject/zephyr=ZEPHYR_BASE, 0
+    84	-- @@ C, -ftls-model=local-exec, 0
+    85	-- @@ C, -Wvla, 0
+    86	-- @@ C, -fmacro-prefix-map=C:/a/sdk-ng/sdk-ng/zephyrproject/zephyr/samples/hello_world=CMAKE_SOURCE_DIR, 1
+    87	-- @@ C, -fmacro-prefix-map=C:/a/sdk-ng/sdk-ng/zephyrproject/zephyr=ZEPHYR_BASE, 1
     88	-- @@ C, -fmacro-prefix-map=C:/a/sdk-ng/sdk-ng/zephyrproject=WEST_TOPDIR, 1
-    89	-- @@ C, -ffunction-sections, 0
+    89	-- @@ C, -ffunction-sections, 1
     90	-- @@ C, -fdata-sections, 1
-    91	-- Configuring done (26.7s)
+    91	-- Configuring done (26.4s)
     92	-- Generating done (0.5s)
     93	-- Build files have been written to: C:/a/sdk-ng/sdk-ng/zephyrproject/zephyr/samples/hello_world/build

For full log, see https://gist.github.com/stephanosio/515697800f63484dc94568edff48c407.

To reproduce

On Windows:

1. Download Zephyr SDK LLVM toolchain and set ZEPHYR_TOOLCHAIN_VARIANT=zephyr-llvm.
2. Check out Zephyr collab-sdk-0.18-dev branch.
3. Apply the following patch on Zephyr repository:

diff --git a/cmake/modules/extensions.cmake b/cmake/modules/extensions.cmake
index d5cd84256d2..a52e793d6e8 100644
--- a/cmake/modules/extensions.cmake
+++ b/cmake/modules/extensions.cmake
@@ -1174,6 +1174,7 @@ function(zephyr_check_compiler_flag lang option check)
   endif()

   check_compiler_flag(${lang} "${possibly_translated_option}" inner_check)
+  message(STATUS "@@@ check_compiler_flag: ${lang} ${possibly_translated_option} ${inner_check}")

   set(${check} ${inner_check} PARENT_SCOPE)

4. Prepare build directory for samples/hello_world:

cd samples/hello_world
mkdir build
cd build

5. From build directory, run the following commands twice, observing the CMake run results:

rm -rf ${ZEPHYR_BASE}/.cache
cmake -GNinja -DBOARD=mps2/an385 ..

Notes

• Even in the same run, the result for zephyr_check_compiler_flag(C "" result) differ -- this seems to be completely random:

     75	-- @@ C, , 1
     76	-- @@ C, , 0
     77	-- @@ C, , 0
     78	-- @@ C, , 1
     79	-- @@ C, , 0
     80	-- @@ C, , 1

• CMake version does not seem to affect this -- tested with CMake 3.22.0 and 3.30.1.