fail to get ra and bp

[bjgnu@sunnorth.com.cn]

Hi all,

The prologue has two insns ---- push ra and push bp.
When back tracing and printing variables, gdb will look for return address 
of this frame and frame pointer on stack.
Unfortunately, If compiling with -O2, the two insns are probably deleted. 
So, GDB will not get ra and bp value.

It seems MIPS also fail to do this.
Anyone has any thought?
 
Thanks.
ligang