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    SubjectRe: BUG: GCC-4.4.x changes the function frame on some functions
    On Thu, Nov 19, 2009 at 6:59 PM, Steven Rostedt <> wrote:
    > On Thu, 2009-11-19 at 09:39 -0800, Linus Torvalds wrote:
    >> > This modification leads to a hard to solve problem in the kernel
    >> > function graph tracer which assumes that the stack looks like:
    >> >
    >> >        return address
    >> >        saved  ebp
    >> Umm. But it still does, doesn't it? That
    >>       pushl  -0x4(%edi)
    >>       push   %ebp
    >> should do it - the "-0x4(%edi)" thing seems to be trying to reload the
    >> return address. No?
    > Yes that is what it is doing. The problem we have is that it is putting
    > into the frame pointer a "copy" of the return address, and not the
    > actual pointer. Which is fine for the function tracer, but breaks the
    > function graph tracer (which is a much more powerful tracer).
    > Technically, this is all that mcount must have. And yes, we are making
    > an assumption that the return address in the frame pointer is the one
    > that will be used to leave the function. But the reason for making this
    > copy just seems to be all messed up.
    > I don't know if the ABI says anything about the return address in the
    > frame pointer must be the actual return address. But it would be nice if
    > the gcc folks would let us guarantee that it is.

    Note that I only can reproduce the issue with
    -mincoming-stack-boundary=2, not with -mpreferred-stack-boundary=2.
    you didn't provide us with a testcase either ... so please open
    a bugzilla and attach preprocessed source of a file that
    shows the problem, note the function it happens in and provide
    the command-line options you used for building.

    Otherwise it's going to be all speculation on our side.

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      Last update: 2009-11-19 19:05    [W:0.022 / U:6.084 seconds]
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