On Thu, 19 Nov 2009, Thomas Gleixner wrote:
Can the GCC folks please shed some light on this:
standard function start:
push %ebp
mov %esp, %ebp
....
call mcount
modified function start on a handful of functions only seen with gcc
4.4.x on x86 32 bit:
push %edi
lea 0x8(%esp),%edi
and $0xfffffff0,%esp
pushl -0x4(%edi)
push %ebp
mov %esp,%ebp
...
call mcount
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
With the modified function start sequence this is not longer true and
the manipulation of the return address on the stack fails silently.
Neither gcc 4.3 nor gcc 3.4 are generating such function frames, so it
looks like a gcc 4.4.x feature.
There is no real obvious reason why the edi magic needs to be done
_before_
push %ebp
mov %esp,%ebp
Thanks,
tglx
