From: Steven Rostedt <rostedt@goodmis.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Song Liu <songliubraving@fb.com>, Kairui Song <kasong@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v3 2/4] objtool: Add support for C jump tables
Date: Thu, 27 Jun 2019 08:58:04 -0400 [thread overview]
Message-ID: <20190627085804.070a9541@gandalf.local.home> (raw)
In-Reply-To: <20190627024700.q4rkcbhmrna6ev4y@treble>
On Wed, 26 Jun 2019 21:47:00 -0500
Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Wed, Jun 26, 2019 at 06:42:40PM -0700, Alexei Starovoitov wrote:
> > > @@ -1035,9 +1038,18 @@ static struct rela *find_switch_table(struct objtool_file *file,
> > >
> > > /*
> > > * Make sure the .rodata address isn't associated with a
> > > - * symbol. gcc jump tables are anonymous data.
> > > + * symbol. GCC jump tables are anonymous data.
> > > + *
> > > + * Also support C jump tables which are in the same format as
> > > + * switch jump tables. Each jump table should be a static
> > > + * local const array named "jump_table" for objtool to
> > > + * recognize it.
> >
> > Nacked-by: Alexei Starovoitov <ast@kernel.org>
> >
> > It's not acceptable for objtool to dictate kernel naming convention.
>
> Abrasive nack notwithstanding, I agree it's not ideal.
>
> How about the following approach instead? This is the only other way I
> can think of to annotate a jump table so that objtool can distinguish
> it:
>
> #define __annotate_jump_table __section(".jump_table.rodata")
>
> Then bpf would just need the following:
>
> - static const void *jumptable[256] = {
> + static const void __annotate_jump_table *jumptable[256] = {
>
> This would be less magical and fragile than my original approach.
>
> I think the jump table would still be placed with all the other rodata,
> like before, because the vmlinux linker script recognizes the section
> ".rodata" suffix and bundles them all together.
>
After finally getting a chance to skim through this lovely thread, I
was going to suggest exactly this. This is the way we usually handle
"special" data.
As it appears that Alexei is good with this approach, please go this
route.
Thanks!
-- Steve
next prev parent reply other threads:[~2019-06-27 12:58 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-27 0:33 [PATCH v3 0/4] x86: bpf unwinder fixes Josh Poimboeuf
2019-06-27 0:33 ` [PATCH v3 1/4] perf/x86: Always store regs->ip in perf_callchain_kernel() Josh Poimboeuf
2019-06-27 22:22 ` [tip:x86/urgent] " tip-bot for Song Liu
2019-06-27 0:33 ` [PATCH v3 2/4] objtool: Add support for C jump tables Josh Poimboeuf
2019-06-27 1:42 ` Alexei Starovoitov
2019-06-27 2:47 ` Josh Poimboeuf
2019-06-27 2:54 ` Alexei Starovoitov
2019-06-27 3:44 ` Josh Poimboeuf
2019-06-27 3:56 ` Josh Poimboeuf
2019-06-27 4:38 ` Alexei Starovoitov
2019-06-27 12:58 ` Steven Rostedt [this message]
2019-06-27 0:33 ` [PATCH v3 3/4] bpf: Fix ORC unwinding in non-JIT BPF code Josh Poimboeuf
2019-06-27 0:57 ` Alexei Starovoitov
2019-06-27 1:06 ` Josh Poimboeuf
2019-06-27 1:22 ` Alexei Starovoitov
2019-06-27 1:30 ` Josh Poimboeuf
2019-06-27 0:33 ` [PATCH v3 4/4] x86/unwind/orc: Fall back to using frame pointers for generated code Josh Poimboeuf
2019-06-27 22:22 ` [tip:x86/urgent] " tip-bot for Josh Poimboeuf
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190627085804.070a9541@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=alexei.starovoitov@gmail.com \
--cc=bp@alien8.de \
--cc=jpoimboe@redhat.com \
--cc=kasong@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=songliubraving@fb.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).