Thomas Gleixner wrote: > 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
Sure there is: unless you do the adjustment first %ebp won't be 16-aligned. We're aligning the stack properly, as per the ABI requirements. Can't you just fix the tracer? Andrew.
