From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
David Laight <David.Laight@aculab.com>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [RFC PATCH 1/3] static_call: Add static call infrastructure
Date: Mon, 12 Nov 2018 05:39:38 +0100 [thread overview]
Message-ID: <CAKv+Gu-hs7cRjkAAzk7hUqoXWw1vQDvUGQaKnyALrPvW-TTLzA@mail.gmail.com> (raw)
In-Reply-To: <20181112030722.da5cxslvlmdgttsw@treble>
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.
next prev parent reply other threads:[~2018-11-12 4:39 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 21:15 [PATCH RFC 0/3] Static calls Josh Poimboeuf
2018-11-08 21:15 ` [RFC PATCH 1/3] static_call: Add static call infrastructure Josh Poimboeuf
2018-11-09 9:51 ` Ard Biesheuvel
2018-11-09 14:55 ` Josh Poimboeuf
2018-11-09 13:39 ` Ard Biesheuvel
2018-11-09 15:10 ` Josh Poimboeuf
2018-11-09 15:14 ` Ard Biesheuvel
2018-11-09 17:25 ` Ard Biesheuvel
2018-11-09 17:31 ` Josh Poimboeuf
2018-11-09 17:33 ` Ard Biesheuvel
2018-11-09 17:46 ` Josh Poimboeuf
2018-11-09 17:52 ` Ard Biesheuvel
2018-11-09 17:53 ` Ard Biesheuvel
2018-11-09 19:03 ` Josh Poimboeuf
2018-11-09 19:12 ` Ard Biesheuvel
2018-11-09 17:33 ` Josh Poimboeuf
2018-11-09 18:33 ` Steven Rostedt
2018-11-09 19:35 ` Josh Poimboeuf
2018-11-09 19:57 ` Steven Rostedt
2018-11-09 20:34 ` Josh Poimboeuf
2018-11-10 5:10 ` Steven Rostedt
2018-11-10 11:58 ` Ard Biesheuvel
2018-11-10 13:09 ` Steven Rostedt
2018-11-12 3:07 ` Josh Poimboeuf
2018-11-12 4:39 ` Ard Biesheuvel [this message]
2018-11-12 4:56 ` Josh Poimboeuf
2018-11-12 5:02 ` Ard Biesheuvel
2018-11-10 11:56 ` Ard Biesheuvel
2018-11-08 21:15 ` [RFC PATCH 2/3] x86/static_call: Add x86 unoptimized static call implementation Josh Poimboeuf
2018-11-08 21:15 ` [RFC PATCH 3/3] x86/static_call: Add optimized static call implementation for 64-bit Josh Poimboeuf
2018-11-08 21:24 ` [PATCH RFC 0/3] Static calls Josh Poimboeuf
2018-11-09 7:28 ` Ingo Molnar
2018-11-09 7:50 ` Ingo Molnar
2018-11-09 13:50 ` Ard Biesheuvel
2018-11-09 15:20 ` Josh Poimboeuf
2018-11-10 23:20 ` Peter Zijlstra
2018-11-11 13:42 ` Ard Biesheuvel
2018-11-11 14:25 ` Peter Zijlstra
2018-11-09 14:45 ` Josh Poimboeuf
2018-11-12 5:02 ` Ingo Molnar
2018-11-12 5:30 ` Josh Poimboeuf
2018-11-12 9:39 ` Ard Biesheuvel
2018-11-12 22:52 ` Josh Poimboeuf
2018-11-12 17:03 ` Steven Rostedt
2018-11-12 22:56 ` Josh Poimboeuf
2018-11-12 5:34 ` Andy Lutomirski
2018-11-09 15:16 ` Andy Lutomirski
2018-11-09 15:21 ` Josh Poimboeuf
2018-11-09 16:41 ` Josh Poimboeuf
2018-11-09 18:42 ` Steven Rostedt
2018-11-09 19:05 ` Andy Lutomirski
2018-11-09 19:37 ` Steven Rostedt
2018-11-09 19:44 ` Josh Poimboeuf
2018-11-09 19:59 ` Steven Rostedt
2018-11-09 20:36 ` Josh Poimboeuf
2018-11-10 15:13 ` Masami Hiramatsu
2018-11-09 20:53 ` Rasmus Villemoes
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