hi folks, Ive written a pair of patches which have an issue with __initdata [PATCH 1/3] bug.h: add BUILD_BUG_DECL, usable at file scope [PATCH 2/3] bug.h: add test/demo module 1st one declares a BUILD_BUG_DECL(name, condition) which breaks compile if the condition is true, much like the other *BUG* macros. Its usable at file scope, which lets it verify that 2 arrays are the same size: int arr1[] = {1,2,3}; int arr2[] = {1,2,4}; BUILD_BUG_DECL(arr1_VS_arr2, ARRAY_SIZE(arr1) != ARRAY_SIZE( arr2)); heres the macro: +#define BUILD_BUG_DECL(name, cond) \ + static __initdata struct { \ + int BUILD_BUG_DECL_ ## name[1 - 2*!!(cond)]; \ + } BUILD_BUG_DECL_ ##name[0] __attribute__((unused)) + which expands the above like: static __attribute__ ((__section__(".init.data"))) struct { int BUILD_BUG_DECL_arr1_VS_arr1[1 - 2*!!(sizeof(arr1) != sizeof(arr2))]; } BUILD_BUG_DECL_arr1_VS_arr1[0] __attribute__((unused)); It works as pretty much as intended, but there are a few wrinkes, as exposed by the run-time part of the test module (patch 2). The macro attempts to create no storage (by sizing the array as [0]), and put it into the .init.data section of the object code. The test module does 3 things: 1 - proves the macro works. Remove the // on commented BUILD_BUG_DECL statements to try for yourself. 2 - references the variable defined by the macro, during module_init. Printing that value works, its always 0, why ? I thought that the __attribute__((unused)) would have prevented or warned about this access. I also tried __attribute__((nodref, unused)), but compiler warned about it, so I pulled that out. 3 - references the variable defined by the macro, during runtime. ie: $> cat /sys/module/build-asserts/cbint That gets a paging error. This makes sense, as the .init.data has been freed after module_init is done. Why doesnt the compiler warn or error about referencing an __initdata var from a non-__init function ?