Messages in this thread | | | From | Ard Biesheuvel <> | Date | Mon, 12 Nov 2018 05:39:38 +0100 | Subject | Re: [RFC PATCH 1/3] static_call: Add static call infrastructure |
| |
On 12 November 2018 at 04:07, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > On Sat, Nov 10, 2018 at 08:09:17AM -0500, Steven Rostedt wrote: >> On Sat, 10 Nov 2018 12:58:08 +0100 >> Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: >> >> >> > > The complaint is on: >> > > >> > > DEFINE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); >> > > >> > > And the previous definition is on: >> > > >> > > DECLARE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); \ >> > > >> > >> > Does the DECLARE really need the __ADDRESSABLE? Its purpose is to >> > ensure that symbols with static linkage are not optimized away, but >> > since the reference is from a header file, the symbol should have >> > external linkage anyway. > > Yes, DECLARE needs the __ADDRESSABLE. In the case where DECLARE > is used, but DEFINE is not, GCC strips the symbol. >
I assume DECLARE() is intended for use in header files, and DEFINE() for source files, no?
Doesn't that mean that whatever symbol __ADDRESSABLE() refers to should have external linkage, in which case it it addressable anyway? Or are we talking about some LTO / --gc-sections use case here?
>> I applied the following change and it compiled fine: >> >> diff --git a/include/linux/static_call.h b/include/linux/static_call.h >> index 90b580b95303..5f8a0f0e77be 100644 >> --- a/include/linux/static_call.h >> +++ b/include/linux/static_call.h >> @@ -108,8 +108,6 @@ extern void arch_static_call_poison_tramp(unsigned long insn); >> #define DECLARE_STATIC_CALL(key, func) \ >> extern struct static_call_key key; \ >> extern typeof(func) STATIC_CALL_TRAMP(key); \ >> - /* Preserve the ELF symbol so objtool can access it: */ \ >> - __ADDRESSABLE(key) >> >> #define DEFINE_STATIC_CALL(key, _func) \ >> DECLARE_STATIC_CALL(key, _func); \ >> @@ -117,7 +115,9 @@ extern void arch_static_call_poison_tramp(unsigned long insn); >> .func = _func, \ >> .site_mods = LIST_HEAD_INIT(key.site_mods), \ >> }; \ >> - ARCH_STATIC_CALL_TEMPORARY_TRAMP(key) >> + ARCH_STATIC_CALL_TEMPORARY_TRAMP(key); \ >> + /* Preserve the ELF symbol so objtool can access it: */ \ >> + __ADDRESSABLE(key) >> >> #define static_call(key, args...) STATIC_CALL_TRAMP(key)(args) > > Adding __ADDRESSABLE to the DEFINE macro doesn't do any good. By > definition, the key is defined in the .o file, so the symbol already > exists. > > The issue you're seeing is really an issue with the __ADDRESSABLE macro > not creating unique symbol names. This should fix it: > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index 06396c1cf127..4bb73fd918b5 100644 > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -282,7 +282,7 @@ unsigned long read_word_at_a_time(const void *addr) > */ > #define __ADDRESSABLE(sym) \ > static void * __section(".discard.addressable") __used \ > - __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; > + __UNIQUE_ID(__addressable_##sym) = (void *)&sym; > > /** > * offset_to_ptr - convert a relative memory offset to an absolute pointer
Not sure if it matters, but we'll end up with a lot more stuff in .discard.addressable this way.
| |