On Wed, Oct 10, 2018 at 01:16:05PM -0500, Josh Poimboeuf wrote: > On Wed, Oct 10, 2018 at 11:03:43AM -0700, Andy Lutomirski wrote: > > > +#define DECLARE_STATIC_CALL(tramp, func) \ > > > + extern typeof(func) tramp; \ > > > + static void __used __section(.discard.static_call_tramps) \ > > > + *__static_call_tramp_##tramp = tramp > > > + > > > > Confused. What's the __static_call_tramp_##tramp variable for? And > > why is a DECLARE_ macro defining a variable? > > This is the magic needed for objtool to find all the call sites. > > The variable itself isn't needed, but the .discard.static_call_tramps > entry is. Objtool reads that section to find out which function call > sites are targeted to a static call trampoline.
To clarify: objtool reads that section to find out which functions are really static call trampolines. Then it annotates all the instructions which call/jmp to those trampolines. Those annotations are then read by the kernel. -- Josh
