building kernel with -O

[Peter Teoh]

On Thu, Jul 31, 2014 at 12:59 AM, Xin Tong <trent.tong at gmail.com> wrote:

> why can not __builtin_return_address() be made *never* inline and use
> current level+1 to get the return address of the function of interest.  For
> any stack introspection, having 1 more level will not hurt functionality.
>

Actually, the answer for your remark is "impossible" - in the case when the
kernel is compiled without frame pointer.   (CONFIG_FRAME_POINTER=n) which
is true for certain variant of RHEL / CentOS.   Without the availability of
EBP on the stack, there is no way to know when to stop reading the stack to
retrieve the previous stackframe.   Of course u can statically walk the
disassembly of the function and see how much stack space the particular
function has allocated.   But that requires implementing a disassembler in
the kernel.



>
> given its explanation below
>
> — Built-in Function: void * *__builtin_return_address* (unsigned int level
> )
>
> This function returns the return address of the current function, or of
> one of its callers. The level argument is number of frames to scan up the
> call stack. A value of 0 yields the return address of the current
> function, a value of 1 yields the return address of the caller of the
> current function, and so forth. When inlining the expected behavior is that
> the function returns the address of the function that is returned to. To
> work around this behavior use the noinline function attribute.
>
>
>
>

-- 
Regards,
Peter Teoh
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