Messages in this thread | | | From | Ard Biesheuvel <> | Date | Thu, 28 Jun 2018 11:02:36 +0200 | Subject | Re: [PATCH 2/5] kernel/jump_label: implement generic support for relative references |
| |
On 28 June 2018 at 10:50, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, Jun 27, 2018 at 06:06:01PM +0200, Ard Biesheuvel wrote: >> diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h >> index 86ec0652d3b1..aa203dffe72c 100644 >> --- a/include/linux/jump_label.h >> +++ b/include/linux/jump_label.h >> @@ -121,6 +121,32 @@ struct static_key { >> #include <asm/jump_label.h> >> >> #ifndef __ASSEMBLY__ >> +#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE >> + >> +struct jump_entry { >> + int code; >> + int target; >> + int key; >> +}; > > I much prefer you use 'u32' there. >
Actually, they are signed so that would be s32. But yeah, I can change that.
> >> +static void jump_label_swap(void *a, void *b, int size) >> +{ >> + long delta = (unsigned long)a - (unsigned long)b; >> + struct jump_entry *jea = a; >> + struct jump_entry *jeb = b; >> + struct jump_entry tmp = *jea; >> + >> + jea->code = jeb->code - delta; >> + jea->target = jeb->target - delta; >> + jea->key = jeb->key - delta; >> + >> + jeb->code = tmp.code + delta; >> + jeb->target = tmp.target + delta; >> + jeb->key = tmp.key + delta; >> +} >> + >> static void >> jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop) >> { >> @@ -56,7 +72,9 @@ jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop) >> >> size = (((unsigned long)stop - (unsigned long)start) >> / sizeof(struct jump_entry)); >> - sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL); >> + sort(start, size, sizeof(struct jump_entry), jump_label_cmp, >> + IS_ENABLED(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE) ? jump_label_swap >> + : NULL); >> } > > That will result in jump_label_swap being an unused symbol for some > compile options. >
No, and isn't that the point of IS_ENABLED()? The compiler sees a reference to jump_label_swap(), so it won't complain about it being unused.
> Would it not be much nicer to write that like: > > static void jump_label_swap(void *a, void *b, int size) > { > struct jump_entry *jea = a, *jeb = b; > > #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE > long delta = a - b; > > jea->code += delta; > jea->target += delta; > jea->key += delta; > > jeb->code -= delta; > jeb->target -= delta; > jeb->key -= delta; > #else > > swap(*jea, *jeb); > } > > And then unconditionally use jump_label_swap().
Meh. I thought IS_ENABLED() was preferred over #ifdef, no? That way, the compiler always sees the code, and simply discards it without complaining if it ends up left unused.
| |