Patch "s390: move _text symbol to address higher than zero" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

s390: move _text symbol to address higher than zero

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
s390-move-_text-symbol-to-address-higher-than-zero.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Heiko Carstens <[email protected]>
Date: Thu, 4 May 2017 09:42:22 +0200
Subject: s390: move _text symbol to address higher than zero

From: Heiko Carstens <[email protected]>

[ Upstream commit d04a4c76f71dd5335f8e499b59617382d84e2b8d ]

The perf tool assumes that kernel symbols are never present at address zero. In fact it assumes if functions that map symbols to addresses return zero, that the symbol was not found.

Given that s390's _text symbol historically is located at address zero this yields at least a couple of false errors and warnings in one of perf's test cases about not present symbols ("perf test 1").

To fix this simply move the _text symbol to address 0x200, just behind the initial psw and channel program located at the beginning of the kernel image. This is now hard coded within the linker script.

I tried a nicer solution which moves the initial psw and channel program into an own section. However that would move the symbols within the "real" head.text section to different addresses, since the ".org" statements within head.S are relative to the head.text section. If there is a new section in front, everything else will be moved. Alternatively I could have adjusted all ".org" statements. But this current solution seems to be the easiest one, since nobody really cares where the _text symbol is actually located.

---
 arch/s390/kernel/vmlinux.lds.S |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

@@ -28,8 +28,14 @@ SECTIONS
 {
 	. = 0x00000000;
 	.text : {
-	_text = .;		/* Text and read-only data */
+		/* Text and read-only data */
 		HEAD_TEXT
+		/*
+		 * E.g. perf doesn't like symbols starting at address zero,
+		 * therefore skip the initial PSW and channel program located
+		 * at address zero and let _text start at 0x200.
+		 */
+	_text = 0x200;
 		TEXT_TEXT
 		SCHED_TEXT
 		LOCK_TEXT

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/s390-move-_text-symbol-to-address-higher-than-zero.patch