| Message ID | 20231218161044.215640-1-rf@opensource.cirrus.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | fcbac39b7d5e776bed058281af5d3248b94f1282 |
| Delegated to: | Brendan Higgins |
| Headers | show |
| Series | [1/2] kunit: Allow passing function pointer to kunit_activate_static_stub() | expand |
On Mon, Dec 18, 2023 at 11:10 AM 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> Hello! This seems fine to me. I have tested it and the reasoning behind this seems sensible. However, let's see what David thinks when he returns to office as he is the expert on static stubbing. Reviewed-by: Rae Moar <rmoar@google.com> -Rae > --- > 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 >
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)
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> --- include/kunit/static_stub.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)