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

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Message-ID: <20100715150514.GB14073@merkur.ravnborg.org>
Date:	Thu, 15 Jul 2010 17:05:14 +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>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] tracing: properly align linker defined symbols

On Sat, Jul 10, 2010 at 08:34:59AM +0200, Sam Ravnborg wrote:
> 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

Steven - Zeev reported that this fixed the boot problem.
What is next step?
Do you forward this patch or do you prefer another fix?

	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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