linux-kernel - [PATCH] tracing: properly align linker defined symbols

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Date:	Sat, 10 Jul 2010 08:35:00 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Zeev Tarantov <zeev.tarantov@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Zeev Tarantov <zeev.tarantov@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: [PATCH] tracing: properly align linker defined symbols

Zeev - please try this replacement patch.
The alignmnet is increased to 32 bytes compared to my previous version and
we introduce alignmnet for ftrace_events too.

	Sam

>From 40bedb8fda25d2cf9ecdd41ab48a24104607c37e Mon Sep 17 00:00:00 2001
From: Sam Ravnborg <sam@...nborg.org>
Date: Sat, 10 Jul 2010 08:24:12 +0200
Subject: [PATCH] tracing: properly align linker defined symbols

We define a number of symbols in the linker scipt like this:

    __start_syscalls_metadata = .;
    *(__syscalls_metadata)

But we do not know the alignment of "." when we assign
the __start_syscalls_metadata symbol.
gcc started to uses bigger alignment for structs (32 bytes),
so we saw situations where the linker due to alignment
constraints increased the value of "." after the symbol assignment.

This resulted in boot fails.

Fix this by forcing a 32 byte alignment of "." before the
assignment.

This patch introduces the forced alignment for
ftrace_events and syscalls_metadata.
It may be required in more places.

Reported-by: Zeev Tarantov <zeev.tarantov@...il.com>
Signed-off-by: Sam Ravnborg <sam@...nborg.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
---
 include/asm-generic/vmlinux.lds.h |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 48c5299..4b5902a 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -63,6 +63,12 @@
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)
 
+/*
+ * Align to a 32 byte boundary equal to the
+ * alignment gcc 4.5 uses for a struct
+ */
+#define STRUCT_ALIGN() . = ALIGN(32)
+
 /* The actual configuration determine if the init/exit sections
  * are handled as text/data or they can be discarded (which
  * often happens at runtime)
@@ -166,7 +172,11 @@
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
 	TRACE_PRINTKS()							\
+									\
+	STRUCT_ALIGN();							\
 	FTRACE_EVENTS()							\
+									\
+	STRUCT_ALIGN();							\
 	TRACE_SYSCALLS()
 
 /*
-- 
1.6.0.6

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