I am using the following assembly language program (doNothingProg.s) for
instruction purposes:
.text
.globl main
.type main, @function
main:
pushq %rbp # save caller's frame pointer
movq %rsp, %rbp # establish our frame pointer
movl $0, %eax # return 0 to caller
movq %rbp, %rsp # restore stack pointer
popq %rbp # restore caller's frame pointer
ret # back to caller
I want to set a breakpoint at the first instruction (pushq %rbp) so
students can see how the stack frame is created.
I am running Ubuntu 12.04.
Under a previous version ( GNU gdb 6.8-debian) I could do this.
Under the current version (GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2)
7.4-2012.04) when I set the breakpoint on that line then run the
program, it actually breaks at the third instruction (movl $0, %eax).
I understand that the first two instructions are the prologue to the
actual "work" of this function, and since gdb is intended for higher
level languages, but it is possible to make a mistake in the prologue in
assembly language.
Is there any way to get gdb to honor my request for a breakpoint on the
first instruction of the program? Again, my main goal here is to allow
students to single step through the stack frame set up.
--Bob Plantz
