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    SubjectRe: [PATCH 0/2] [GIT PULL][for 2.6.31] function graph gcc issue

    * Steven Rostedt <rostedt@goodmis.org> wrote:

    > Ingo,
    >
    > The bug I spent two days debugging that Jake found was due to gcc
    > making a copy of the return address into the stack frame and not
    > using it to actually return. The function graph tracer would
    > modify the copy and not the actual location that was used to
    > return to. Thus the accounting of the function graph tracer was
    > corrupted and a nasty crash followed.
    >
    > I found that 32bit x86 when compiled with optimize for size caused
    > this issue in the latest gcc (4.4.0). The first patch makes the
    > function graph tracer depend on !X86_32 || !CC_OPTIMIZE_FOR_SIZE.
    > This way we keep from getting into trouble with a know
    > configuration that breaks.
    >
    > Then next patch adds to x86 (both 32bit and 64bit) a test of the
    > frame pointer to make sure that the return actually goes to where
    > we expect it to.
    >
    > When debugging Jakes bug, The first instance was easy to find. It was
    > the timer_stats_update_stats that had a forced cacheline struct as a local.
    > I changed that and it seemed to fix the boot up test. When I enabled
    > function graph at run time, the system crashed again, but this time the
    > crash was hard to find where the issue was. I wrote up this test (patch 2)
    > and I found the problem immediately. In case gcc changes, we want to be
    > able to detect it right away before the tracer does anything dangerous.
    >
    >
    > Please pull the latest tip/tracing/urgent-1 tree, which can be found at:
    >
    > git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
    > tip/tracing/urgent-1
    >
    >
    > Steven Rostedt (2):
    > function-graph: disable when both x86_32 and optimize for size are configured
    > function-graph: add stack frame test
    >
    > ----
    > arch/powerpc/kernel/ftrace.c | 2 +-
    > arch/s390/kernel/ftrace.c | 2 +-
    > arch/x86/Kconfig | 1 +
    > arch/x86/kernel/entry_32.S | 2 +
    > arch/x86/kernel/entry_64.S | 2 +
    > arch/x86/kernel/ftrace.c | 6 +++-
    > include/linux/ftrace.h | 4 ++-
    > kernel/trace/Kconfig | 8 +++++++
    > kernel/trace/trace_functions_graph.c | 36 ++++++++++++++++++++++++++++++---
    > 9 files changed, 54 insertions(+), 9 deletions(-)
    > --

    Pulled, thanks Steve!

    What a nasty bug ...

    Ingo


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