From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
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: Sat, 10 Nov 2018 12:58:08 +0100 [thread overview]
Message-ID: <CAKv+Gu-y=O6=dSbCXSaMxkj7LxfL9txzJ4r8Bcf1U0G6JQNUng@mail.gmail.com> (raw)
In-Reply-To: <20181110001023.57f27312@vmware.local.home>
On 10 November 2018 at 06:10, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 9 Nov 2018 14:34:59 -0600
> Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> I'm slowly massaging this to work with tracepoints.
>
> But I hit a snag on this patch.
>
>> On Fri, Nov 09, 2018 at 02:57:46PM -0500, Steven Rostedt wrote:
>> > On Fri, 9 Nov 2018 13:35:05 -0600
>> > Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>> >
>> >
>> > > > > +#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)
>> > > >
>> > > > Does the __ADDRESSABLE(key) need to be in the DECLARE part?
>> > > > If so, there needs to be more explanation than just the comment above
>> > > > it.
>> > >
>> > > For each call site, objtool creates a struct in .static_call_sites:
>> > >
>> > > struct static_call_site {
>> > > s32 addr;
>> > > s32 key;
>> > > };
>> > >
>> > > In order to do that, it needs to create a relocation which references
>> > > the key symbol. If the key is defined in another .o file, then the
>> > > current .o will not have an ELF symbol associated with the key. The
>> > > __ADDRESSABLE(key) thing tells GCC to leave the key symbol in the .o
>> > > file, even though it's not referenced anywhere. That makes objtool's
>> > > job easier, so it doesn't have to edit the symbol table.
>> > >
>> > > I could add a comment saying as much, though it's hard to explain it in
>> > > fewer words than I just did :-)
>> >
>> > Does this have to do with adding the references by relative address?
>> >
>> > In record_mcount, I just picked an existing symbol and referenced that..
>> > But perhaps this is a cleaner way.
>>
>> I think recordmcount is different. It creates references (in
>> __mcount_loc) to functions which are already in the object file, so they
>> already have symbols associated with them.
>>
>> But in this case, when objtool is creating references, the symbol it
>> needs to reference is outside the .o file, so there's no symbol to
>> associate it with.
>>
>
> The __ADDRESSABLE() appears to fail if you have a header with a
> DECLARE_STATIC_CALL() that is included where the DEFINE_STATIC_CALL()
> is, because I'm getting this:
>
> In file included from <command-line>:
> /work/git/linux-trace.git/include/linux/compiler.h:285:11: error: redefinition of ‘__addressable___tp_func_sys_enter40’
> __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
> ^~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/compiler_types.h:53:23: note: in definition of macro ‘___PASTE’
> #define ___PASTE(a,b) a##b
> ^
> /work/git/linux-trace.git/include/linux/compiler.h:285:3: note: in expansion of macro ‘__PASTE’
> __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
> ^~~~~~~
> /work/git/linux-trace.git/include/linux/static_call.h:112:2: note: in expansion of macro ‘__ADDRESSABLE’
> __ADDRESSABLE(key)
> ^~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/static_call.h:115:2: note: in expansion of macro ‘DECLARE_STATIC_CALL’
> DECLARE_STATIC_CALL(key, _func); \
> ^~~~~~~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/tracepoint.h:310:2: note: in expansion of macro ‘DEFINE_STATIC_CALL’
> DEFINE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name);
> ^~~~~~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/trace/define_trace.h:42:2: note: in expansion of macro ‘DEFINE_TRACE_FN’
> DEFINE_TRACE_FN(name, reg, unreg, PARAMS(proto), PARAMS(args))
> ^~~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/trace/events/syscalls.h:18:1: note: in expansion of macro ‘TRACE_EVENT_FN’
> TRACE_EVENT_FN(sys_enter,
> ^~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/compiler.h:285:11: note: previous definition of ‘__addressable___tp_func_sys_enter40’ was here
> __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
> ^~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/compiler_types.h:53:23: note: in definition of macro ‘___PASTE’
> #define ___PASTE(a,b) a##b
> ^
> /work/git/linux-trace.git/include/linux/compiler.h:285:3: note: in expansion of macro ‘__PASTE’
> __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
> ^~~~~~~
> /work/git/linux-trace.git/include/linux/static_call.h:112:2: note: in expansion of macro ‘__ADDRESSABLE’
> __ADDRESSABLE(key)
> ^~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/tracepoint.h:234:2: note: in expansion of macro ‘DECLARE_STATIC_CALL’
> DECLARE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); \
> ^~~~~~~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/tracepoint.h:421:2: note: in expansion of macro ‘__DECLARE_TRACE’
> __DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), \
> ^~~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/tracepoint.h:560:2: note: in expansion of macro ‘DECLARE_TRACE’
> DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
> ^~~~~~~~~~~~~
> /work/git/linux-trace.git/include/trace/events/syscalls.h:18:1: note: in expansion of macro ‘TRACE_EVENT_FN’
> TRACE_EVENT_FN(sys_enter,
>
> 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.
next prev parent reply other threads:[~2018-11-10 11:58 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 [this message]
2018-11-10 13:09 ` Steven Rostedt
2018-11-12 3:07 ` Josh Poimboeuf
2018-11-12 4:39 ` Ard Biesheuvel
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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