• Jeff Mahoney's avatar
    tracing: Fix ftrace_event_call alignment for use with gcc 4.5 · 86c38a31
    Jeff Mahoney authored
    GCC 4.5 introduces behavior that forces the alignment of structures to
     use the largest possible value. The default value is 32 bytes, so if
     some structures are defined with a 4-byte alignment and others aren't
     declared with an alignment constraint at all - it will align at 32-bytes.
     For things like the ftrace events, this results in a non-standard array.
     When initializing the ftrace subsystem, we traverse the _ftrace_events
     section and call the initialization callback for each event. When the
     structures are misaligned, we could be treating another part of the
     structure (or the zeroed out space between them) as a function pointer.
     This patch forces the alignment for all the ftrace_event_call structures
     to 4 bytes.
     Without this patch, the kernel fails to boot very early when built with
     gcc 4.5.
     It's trivial to check the alignment of the members of the array, so it
     might be worthwhile to add something to the build system to do that
     automatically. Unfortunately, that only covers this case. I've asked one
     of the gcc developers about adding a warning when this condition is seen.
    Cc: stable@kernel.org
    Signed-off-by: default avatarJeff Mahoney <jeffm@suse.com>
    LKML-Reference: <4B85770B.6010901@suse.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>