build: Dependency handling for syscall gen for changed API

Fix issue where changing an existing syscall API does not result in
regeneration of syscalls. This causes a build break on incremental
builds. The issue comes from an incorrect assumption that file
modifications result in updates to folder timestamps on Linux. The fix
is to use the same mechanism Windows is using to track file changes,
making explicit deps on header files that have syscalls.

Signed-off-by: Mark Inderhees <[email protected]>

Author: mark-inderhees

CMakeLists.txt

@@ -788,12 +788,12 @@ set(struct_tags_json ${CMAKE_CURRENT_BINARY_DIR}/misc/generated/struct_tags.json
 # The syscalls subdirs txt file is constructed by python containing a list of folders to use for
 # dependency handling, including empty folders.
 # Windows:  The list is used to specify DIRECTORY list with CMAKE_CONFIGURE_DEPENDS attribute.
-# Other OS: The list will update whenever a file is added/removed/modified and ensure a re-build.
+# Other OS: The list file is updated whenever a directory is added or removed.
 set(syscalls_subdirs_txt ${CMAKE_CURRENT_BINARY_DIR}/misc/generated/syscalls_subdirs.txt)
 
-# As syscalls_subdirs_txt is updated whenever a file is modified, this file can not be used for
-# monitoring of added / removed folders. A trigger file is thus used for correct dependency
-# handling. The trigger file will update when a folder is added / removed.
+# As syscalls_subdirs_txt is updated only on directory add or remove, this file can not be used for
+# monitoring of syscall changes. A trigger file is thus used for correct dependency handling. The
+# trigger file will update when syscalls change.
 set(syscalls_subdirs_trigger ${CMAKE_CURRENT_BINARY_DIR}/misc/generated/syscalls_subdirs.trigger)
 
 if(NOT (${CMAKE_HOST_SYSTEM_NAME} STREQUAL Windows))
@@ -812,14 +812,13 @@ execute_process(
 )
 file(STRINGS ${syscalls_subdirs_txt} PARSE_SYSCALLS_PATHS_DEPENDS ENCODING UTF-8)
 
+# Each header file must be monitored as file modifications are not reflected on directory level.
+file(GLOB_RECURSE PARSE_SYSCALLS_HEADER_DEPENDS ${ZEPHYR_BASE}/include/*.h)
+
 if(${CMAKE_HOST_SYSTEM_NAME} STREQUAL Windows)
   # On windows only adding/removing files or folders will be reflected in depends.
   # Hence adding a file requires CMake to re-run to add this file to the file list.
   set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${PARSE_SYSCALLS_PATHS_DEPENDS})
-
-  # Also On Windows each header file must be monitored as file modifications are not reflected
-  # on directory level.
-  file(GLOB_RECURSE PARSE_SYSCALLS_HEADER_DEPENDS ${ZEPHYR_BASE}/include/*.h)
 else()
   # The syscall parsing depends on the folders in order to detect add/removed/modified files.
   # When a folder is removed, CMake will try to find a target that creates that dependency.
@@ -850,10 +849,10 @@ else()
     file(WRITE ${syscalls_subdirs_txt} "")
   endif()
 
-  # On other OS'es, modifying a file is reflected on the folder timestamp and hence detected
+  # On other OS'es, using git checkout is reflected on the folder timestamp and hence detected
   # when using depend on directory level.
   # Thus CMake only needs to re-run when sub-directories are added / removed, which is indicated
-  # using a trigger file.
+  # by syscalls_subdirs_txt being updated.
   set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${syscalls_subdirs_txt})
 endif()