Menu
I'm debugging the goldfish android kernel (version 3.4), with kernel sources.
Now I found that gdb sometimes jump back and forth between lines, e.g consider c source code like the following:
char *XXX;
int a;
...
if (...)
{
}
When I reached the if clause, I type in n and it will jump back to the int a part. Why is that?
If I execute that command again, it would enter the brackets in the if.
If possible, I want to avoid that part, and enter the if directly (of course, if condition matches)
647
Description. This command jumps the program counter to the specified location. The debugger resumes program execution at that point unless it encounters a breakpoint there.
Quitting GDB To exit GDB, use the quit command (abbreviated q ), or type an end-of-file character (usually C-d ). If you do not supply expression , GDB will terminate normally; otherwise it will terminate using the result of expression as the error code.
If you want to execute the entire function with one keypress, type "next" or "n". This is equivalent to the "step over" command of most debuggers. If you want gdb to resume normal execution, type "continue" or "c". gdb will run until your program ends, your program crashes, or gdb encounters a breakpoint.
When I reached the if clause, I type in n and it will jump back to the int a part. Why is that?
Because your code is compiled with optimization on, and the compiler can (and often does) re-arrange instructions of your program in such a way that instructions "belonging" to different source lines are interleaved (code motion optimizations attempt (among other things) to move load instructions to long before their results are needed; this helps to hide memory latency).
If you are using gcc-4.8 or later, build your sources with -Og. Else, see this answer.
122
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
