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 ?
_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
