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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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