I am trying to make sense out of the executable code that GCC (4.4.3) is generating for an x86_64 machine running under Ubuntu Linux. In particular, I don't understand how the code keeps track of stack frames. In the old days, in 32-bit code, I am accustomed to seeing this as a "prologue" in just about every function: push %ebp movl %esp, %ebp Then, at the end of the function, there would either be sub $xx, %esp # Where xx is a number based on GCC's accounting. pop %ebp ret or simply leave ret which accomplishes the same thing: - Set the Stack Pointer to the top of the current frame, just below the return address - Restore the old Frame Pointer value. In 64-bit code, as I see it through an objdump disassembly, many functions do not follow this convention--they do not push %rbp and then save %rsp to %rbp, How does a debugger like GDB build a backtrace? My real goal here to is to try to figure out a reasonable address to consider as the top (highest address) of the user stack when execution reaches the start of a function further into the program, where perhaps the Stack Pointer has moved down. I had at first thought that I could use the old backtrace method: chasing saved Frame Pointer values until the value saved is 0--then, the next one after that can count as the highest practical value. Now, I don't know how to get the equivalent address in 64-bit code. Thanks. Amittai Aviram PhD Student in Computer Science Yale University 646 483 2639 amittai.aviram@xxxxxxxx http://www.amittai.com
