On Thu, 21 Dec 2023 at 18:39, Richard Fitzgerald rf@opensource.cirrus.com wrote:
Swap the arguments to typecheck_fn() in kunit_activate_static_stub() so that real_fn_addr can be either the function itself or a pointer to that function.
This is useful to simplify redirecting static functions in a module. Having to pass the actual function meant that it must be exported from the module. Either making the 'static' and EXPORT_SYMBOL*() conditional (which makes the code messy), or change it to always exported (which increases the export namespace and prevents the compiler inlining a trivial stub function in non-test builds).
With the original definition of kunit_activate_static_stub() the address of real_fn_addr was passed to typecheck_fn() as the type to be passed. This meant that if real_fn_addr was a pointer-to-function it would resolve to a ** instead of a *, giving an error like this:
error: initialization of ‘int (**)(int)’ from incompatible pointer type ‘int (*)(int)’ [-Werror=incompatible-pointer-types] kunit_activate_static_stub(test, add_one_fn_ptr, subtract_one); | ^~~~~~~~~~~~ ./include/linux/typecheck.h:21:25: note: in definition of macro ‘typecheck_fn’ 21 | ({ typeof(type) __tmp = function; \
Swapping the arguments to typecheck_fn makes it take the type of a pointer to the replacement function. Either a function or a pointer to function can be assigned to that. For example:
static int some_function(int x) { /* whatever */ }
int (* some_function_ptr)(int) = some_function;
static int replacement(int x) { /* whatever */ }
Then: kunit_activate_static_stub(test, some_function, replacement); yields: typecheck_fn(typeof(&replacement), some_function);
and: kunit_activate_static_stub(test, some_function_ptr, replacement); yields: typecheck_fn(typeof(&replacement), some_function_ptr);
The two typecheck_fn() then resolve to:
int (*__tmp)(int) = some_function; and int (*__tmp)(int) = some_function_ptr;
Both of these are valid. In the first case the compiler inserts an implicit '&' to take the address of the supplied function, and in the second case the RHS is already a pointer to the same type.
Signed-off-by: Richard Fitzgerald rf@opensource.cirrus.com Reviewed-by: Rae Moar rmoar@google.com
This makes sense to me.
I was a little worried at first that this might actually be adding a layer of indirection (which, given we're keying on the pointer, would've needed to be done carefully), but this is an obvious fix to me.
Reviewed-by: David Gow davidgow@google.com
Cheers, -- David
No changes since V1.
include/kunit/static_stub.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/kunit/static_stub.h b/include/kunit/static_stub.h index 85315c80b303..bf940322dfc0 100644 --- a/include/kunit/static_stub.h +++ b/include/kunit/static_stub.h @@ -93,7 +93,7 @@ void __kunit_activate_static_stub(struct kunit *test,
- The redirection can be disabled again with kunit_deactivate_static_stub().
*/ #define kunit_activate_static_stub(test, real_fn_addr, replacement_addr) do { \
typecheck_fn(typeof(&real_fn_addr), replacement_addr); \
typecheck_fn(typeof(&replacement_addr), real_fn_addr); \ __kunit_activate_static_stub(test, real_fn_addr, replacement_addr); \} while (0)
-- 2.30.2