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SubjectRe: [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@ravnborg.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@gmail.com>
> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.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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