• Mathieu Desnoyers's avatar
    tracepoints: Fix section alignment using pointer array · 65498646
    Mathieu Desnoyers authored
    Make the tracepoints more robust, making them solid enough to handle compiler
    changes by not relying on anything based on compiler-specific behavior with
    respect to structure alignment. Implement an approach proposed by David Miller:
    use an array of const pointers to refer to the individual structures, and export
    this pointer array through the linker script rather than the structures per se.
    It will consume 32 extra bytes per tracepoint (24 for structure padding and 8
    for the pointers), but are less likely to break due to compiler changes.
    commit 7e066fb8 tracepoints: add DECLARE_TRACE() and DEFINE_TRACE()
    added the aligned(32) type and variable attribute to the tracepoint structures
    to deal with gcc happily aligning statically defined structures on 32-byte
    One attempt was to use a 8-byte alignment for tracepoint structures by applying
    both the variable and type attribute to tracepoint structures definitions and
    declarations. It worked fine with gcc 4.5.1, but broke with gcc 4.4.4 and 4.4.5.
    The reason is that the "aligned" attribute only specify the _minimum_ alignment
    for a structure, leaving both the compiler and the linker free to align on
    larger multiples. Because tracepoint.c expects the structures to be placed as an
    array within each section, up-alignment cause NULL-pointer exceptions due to the
    extra unexpected padding.
    (this patch applies on top of -tip)
    Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
    LKML-Reference: <20110126222622.GA10794@Krystal>
    CC: Frederic Weisbecker <fweisbec@gmail.com>
    CC: Ingo Molnar <mingo@elte.hu>
    CC: Thomas Gleixner <tglx@linutronix.de>
    CC: Andrew Morton <akpm@linux-foundation.org>
    CC: Peter Zijlstra <peterz@infradead.org>
    CC: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
module.c 87.7 KB