linux-kernel - [3.16.y-ckt stable] Patch "ARC: make sure instruction_pointer() returns unsigned value" has been added to staging queue

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Message-Id: <1439297729-29631-1-git-send-email-luis.henriques@canonical.com>
Date:	Tue, 11 Aug 2015 13:55:29 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Alexey Brodkin <abrodkin@...opsys.com>
Cc:	arc-linux-dev@...opsys.com, linux-kernel@...r.kernel.org,
	Vineet Gupta <vgupta@...opsys.com>,
	Luis Henriques <luis.henriques@...onical.com>,
	kernel-team@...ts.ubuntu.com
Subject: [3.16.y-ckt stable] Patch "ARC: make sure instruction_pointer() returns unsigned value" has been added to staging queue

This is a note to let you know that I have just added a patch titled

    ARC: make sure instruction_pointer() returns unsigned value

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From c7bc79956a634da40b323e3cf71650a3c08cecd3 Mon Sep 17 00:00:00 2001
From: Alexey Brodkin <abrodkin@...opsys.com>
Date: Mon, 13 Jul 2015 10:25:17 +0300
Subject: ARC: make sure instruction_pointer() returns unsigned value

commit f51e2f1911122879eefefa4c592dea8bf794b39c upstream.

Currently instruction_pointer() returns pt_regs->ret and so return value
is of type "long", which implicitly stands for "signed long".

While that's perfectly fine when dealing with 32-bit values if return
value of instruction_pointer() gets assigned to 64-bit variable sign
extension may happen.

And at least in one real use-case it happens already.
In perf_prepare_sample() return value of perf_instruction_pointer()
(which is an alias to instruction_pointer() in case of ARC) is assigned
to (struct perf_sample_data)->ip (which type is "u64").

And what we see if instuction pointer points to user-space application
that in case of ARC lays below 0x8000_0000 "ip" gets set properly with
leading 32 zeros. But if instruction pointer points to kernel address
space that starts from 0x8000_0000 then "ip" is set with 32 leadig
"f"-s. I.e. id instruction_pointer() returns 0x8100_0000, "ip" will be
assigned with 0xffff_ffff__8100_0000. Which is obviously wrong.

In particular that issuse broke output of perf, because perf was unable
to associate addresses like 0xffff_ffff__8100_0000 with anything from
/proc/kallsyms.

That's what we used to see:
 ----------->8----------
  6.27%  ls       [unknown]                [k] 0xffffffff8046c5cc
  2.96%  ls       libuClibc-0.9.34-git.so  [.] memcpy
  2.25%  ls       libuClibc-0.9.34-git.so  [.] memset
  1.66%  ls       [unknown]                [k] 0xffffffff80666536
  1.54%  ls       libuClibc-0.9.34-git.so  [.] 0x000224d6
  1.18%  ls       libuClibc-0.9.34-git.so  [.] 0x00022472
 ----------->8----------

With that change perf output looks much better now:
 ----------->8----------
  8.21%  ls       [kernel.kallsyms]        [k] memset
  3.52%  ls       libuClibc-0.9.34-git.so  [.] memcpy
  2.11%  ls       libuClibc-0.9.34-git.so  [.] malloc
  1.88%  ls       libuClibc-0.9.34-git.so  [.] memset
  1.64%  ls       [kernel.kallsyms]        [k] _raw_spin_unlock_irqrestore
  1.41%  ls       [kernel.kallsyms]        [k] __d_lookup_rcu
 ----------->8----------

Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
Cc: arc-linux-dev@...opsys.com
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/arc/include/asm/ptrace.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 1bfeec2c0558..2a58af7a2e3a 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -63,7 +63,7 @@ struct callee_regs {
 	long r25, r24, r23, r22, r21, r20, r19, r18, r17, r16, r15, r14, r13;
 };

-#define instruction_pointer(regs)	((regs)->ret)
+#define instruction_pointer(regs)	(unsigned long)((regs)->ret)
 #define profile_pc(regs)		instruction_pointer(regs)

 /* return 1 if user mode or 0 if kernel mode */
--
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