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From: Steven Rostedt <rostedt@goodmis.org>
To: David Daney <ddaney@caviumnetworks.com>
Cc: Jason Baron <jbaron@akamai.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mips@linux-mips.org,
	linuxppc-dev@lists.ozlabs.org, Ingo Molnar <mingo@kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Anton Blanchard <anton@samba.org>, Rabin Vincent <rabin@rab.in>,
	Russell King <linux@armlinux.org.uk>,
	Ralf Baechle <ralf@linux-mips.org>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	Zhigang Lu <zlu@ezchip.com>
Subject: Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes
Date: Mon, 27 Feb 2017 17:09:11 -0500	[thread overview]
Message-ID: <20170227170911.2280ca3e@gandalf.local.home> (raw)
In-Reply-To: <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com>

On Mon, 27 Feb 2017 13:41:13 -0800
David Daney <ddaney@caviumnetworks.com> wrote:

> On 02/27/2017 01:06 PM, Steven Rostedt wrote:
> > On Mon, 27 Feb 2017 11:59:50 -0800
> > David Daney <ddaney@caviumnetworks.com> wrote:
> >  
> >> For me the size is not the important issue, it is the alignment of the
> >> struct jump_entry entries in the table.  I don't understand how your
> >> patch helps, and I cannot Acked-by unless I understand what is being
> >> done and can see that it is both correct and necessary.  
> >
> > You brought up a very good point and I'm glad that I had Jason Cc all
> > the arch maintainers in one patch.
> >
> > I think jump_labels may be much more broken than we think, and Jason's
> > fix doesn't fix anything. We had this same issues with tracepoints.
> >
> > I'm looking at jump_label_init, and how we iterate over an array of
> > struct jump_entry's that was put together by the linker. The problem is
> > that jump_entry is not a power of 2 in size.
> >  
> 
> ELF sections may have an ENTSIZE property exactly for arrays.  Since 
> each jump_entry will have a unique value they cannot be merged, but we 
> can tell the assembler they are an array and get them properly packed. 
> Perhaps something like (untested):
> 
>     .pushsection __jump_table,  \"awM\",@progbits,24
>     FOO
>     .popsection
> 

And the linker will honor this too?

-- Steve

WARNING: multiple messages have this Message-ID (diff)
From: rostedt@goodmis.org (Steven Rostedt)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] jump_label: align jump_entry table to at least 4-bytes
Date: Mon, 27 Feb 2017 17:09:11 -0500	[thread overview]
Message-ID: <20170227170911.2280ca3e@gandalf.local.home> (raw)
In-Reply-To: <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com>

On Mon, 27 Feb 2017 13:41:13 -0800
David Daney <ddaney@caviumnetworks.com> wrote:

> On 02/27/2017 01:06 PM, Steven Rostedt wrote:
> > On Mon, 27 Feb 2017 11:59:50 -0800
> > David Daney <ddaney@caviumnetworks.com> wrote:
> >  
> >> For me the size is not the important issue, it is the alignment of the
> >> struct jump_entry entries in the table.  I don't understand how your
> >> patch helps, and I cannot Acked-by unless I understand what is being
> >> done and can see that it is both correct and necessary.  
> >
> > You brought up a very good point and I'm glad that I had Jason Cc all
> > the arch maintainers in one patch.
> >
> > I think jump_labels may be much more broken than we think, and Jason's
> > fix doesn't fix anything. We had this same issues with tracepoints.
> >
> > I'm looking at jump_label_init, and how we iterate over an array of
> > struct jump_entry's that was put together by the linker. The problem is
> > that jump_entry is not a power of 2 in size.
> >  
> 
> ELF sections may have an ENTSIZE property exactly for arrays.  Since 
> each jump_entry will have a unique value they cannot be merged, but we 
> can tell the assembler they are an array and get them properly packed. 
> Perhaps something like (untested):
> 
>     .pushsection __jump_table,  \"awM\", at progbits,24
>     FOO
>     .popsection
> 

And the linker will honor this too?

-- Steve

  reply	other threads:[~2017-02-27 22:10 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-27 18:49 [PATCH] jump_label: align jump_entry table to at least 4-bytes Jason Baron
2017-02-27 18:49 ` Jason Baron
2017-02-27 18:57 ` David Daney
2017-02-27 18:57   ` David Daney
2017-02-27 19:18   ` Jason Baron
2017-02-27 19:18     ` Jason Baron
2017-02-27 19:59     ` David Daney
2017-02-27 19:59       ` David Daney
2017-02-27 21:06       ` Steven Rostedt
2017-02-27 21:06         ` Steven Rostedt
2017-02-27 21:41         ` David Daney
2017-02-27 21:41           ` David Daney
2017-02-27 22:09           ` Steven Rostedt [this message]
2017-02-27 22:09             ` Steven Rostedt
2017-02-27 22:21             ` David Daney
2017-02-27 22:21               ` David Daney
2017-02-27 22:21               ` David Daney
2017-02-27 22:36               ` Steven Rostedt
2017-02-27 22:36                 ` Steven Rostedt
2017-02-27 22:45                 ` David Daney
2017-02-27 22:45                   ` David Daney
2017-02-27 22:50                   ` Jason Baron
2017-02-27 22:50                     ` Jason Baron
2017-02-27 23:34                     ` David Daney
2017-02-27 23:34                       ` David Daney
2017-02-28  4:55                     ` Sachin Sant
2017-02-28 16:21                       ` Steven Rostedt
2017-02-28 16:21                         ` Steven Rostedt
2017-02-28 18:16                         ` David Daney
2017-02-28 18:16                           ` David Daney
2017-02-28 18:39                           ` Jason Baron
2017-02-28 18:39                             ` Jason Baron
2017-02-28 19:05                             ` David Daney
2017-02-28 19:05                               ` David Daney
2017-02-28 19:22                               ` David Daney
2017-02-28 19:22                                 ` David Daney
2017-02-28 19:34                                 ` Jason Baron
2017-02-28 19:34                                   ` Jason Baron
2017-02-28 20:15                                   ` David Daney
2017-02-28 20:15                                     ` David Daney
2017-02-28 20:15                                     ` David Daney
2017-02-28 22:41                                     ` Jason Baron
2017-02-28 22:41                                       ` Jason Baron
2017-03-01  6:34                                       ` Michael Ellerman
2017-03-01  6:34                                         ` Michael Ellerman
2017-03-01 16:40                                         ` David Daney
2017-03-01 16:40                                           ` David Daney
2017-03-01 20:02                                           ` Jason Baron
2017-03-01 20:02                                             ` Jason Baron
2017-03-01 21:12                                             ` David Daney
2017-03-01 21:12                                               ` David Daney
2017-03-01  7:12                                       ` Sachin Sant
2017-03-01  7:12                                         ` Sachin Sant
2017-02-27 22:58                   ` Steven Rostedt
2017-02-27 22:58                     ` Steven Rostedt
2017-03-06  2:16               ` [PATCH] MIPS: jump_lable: Give __jump_table elements an entsize kbuild test robot
2017-03-06  2:16                 ` kbuild test robot

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