On Fri, Feb 28, 2020 at 05:24:58PM +0000, Rasmus Villemoes wrote:
On 28/02/2020 16.46, Tom Rini wrote:
On Fri, Feb 28, 2020 at 08:42:21AM +0000, Rasmus Villemoes wrote:
On 28/02/2020 00.40, Simon Glass wrote:
Using if() is preferable to #if if there is no cost.
Completely agree, and I also prefer to have the linker eliminate unused functions rather than cluttering the C code with #ifdefs. But that can't be used in this case.
Anyway, this wasn't primarily to save 112 bytes or whatnot from the U-Boot image, just to use one style a little more consistently.
Perhaps we could come up with a little more macro-magic? In psuedo-code: #define RESERVE_INIT_SEQ_F_ENTRY(fn) \ #if CONFIG_IS_ENABLED(toupper(fn)) reserve_##fn #endif #endif
I'm afraid that's rather far from something that can be implemented; macros cannot expand to other preprocessor directives, and toupper is also pretty hard to do.
Darn. I would have been willing to move to reserve_FUNCTION if it would have otherwise worked.
What we could do if we want to reduce #ifdefs while still eliminating the no-op functions is to replace
#ifdef CONFIG_FOO static int foo_init(void) { blabla; return 0; } #endif ... init_sequence_f[] = { ... #ifdef CONFIG_FOO foo_init, #endif ... }
by
static int foo_init(void) { /* always defined */ blabla; return 0; }
init_sequence_f[] = { ... IS_ENABLED(CONFIG_FOO) ? foo_init : NULL, ... }
and teach the iterator to ignore NULL entries (I don't remember if we use a NULL terminator or use ARRAY_SIZE; if the former one should switch to the latter). It will still cost sizeof(void*) for the NULL entries, but the function bodies (and on powerpc the .fixups) should be eliminated, and there's not an #ifdef in sight.
That sounds pretty nice actually. If you're so inclined I'd like to see it.