Re: [PATCH] tracing: properly align linker defined symbols

[Zeev Tarantov]

On Sat, Jul 10, 2010 at 09:35, Sam Ravnborg <sam@xxxxxxxxxxxx> 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
>
> From 40bedb8fda25d2cf9ecdd41ab48a24104607c37e Mon Sep 17 00:00:00 2001
> From: Sam Ravnborg <sam@xxxxxxxxxxxx>
> 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@xxxxxxxxx>
> Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> ---
>  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
>
>

2.6.35-rc4 from tarball patched with only this, same config & same
compiler boots fine.

Tested-by: Zeev Tarantov <zeev.tarantov@xxxxxxxxx>

-Zeev
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