This leaves me in gdb. The target program is not running. Providing an argument to the li command causes it to list ten lines centered around the value of the argument. We still do not see the entire loop. Pressing the Enter key tells gdb to repeat the immediately previous command. From the listed source code, we can see that the decision to exit the loop is made on line 29 in the source code.
The jump to the allDone label will occur if the cmpb instruction on line 28 shows that the rsi register is pointing to a byte that contains zero — the ASCII NUL character.
I set a breakpoint at line 29 so we can see what esi is pointing to. I also set a breakpoint at line 37, the target of the jump. Control then returns to the gdb program. The left-hand column shows the contents of the register in hexadecimal, and the right-hand column is in decimal.
Addresses are usually stated in hexadecimal, so the contents of registers that are supposed to hold only addresses are not converted to decimal. Since our primary interest is the rsi register, we can simplify the display by explicitly specifying which register s to display. FMT is a repeat count followed by a format letter and a size letter. Format letters are o octal , x hex , d decimal , u unsigned decimal , t binary , f float , a address , i instruction , c char and s string.
Size letters are b byte , h halfword , w word , g giant, 8 bytes. The specified number of objects of the specified size are printed according to the format. Defaults for format and size letters are those previously used. Default count is 1. Default address is following last thing printed with this command or "print".
There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many of them. To explicitly load shared library symbols, use the sharedlibrary command:. Sometimes you may wish that GDB stops and gives you control when any of shared library events happen. Use the set stop-on-solib-events command for this:. Shared libraries are also supported in many cross or remote debugging configurations.
A copy of the target's libraries need to be present on the host system; they need to be the same as the target libraries, although the copies on the target can be stripped as long as the copies on the host are not. For remote debugging, you need to tell GDB where the target libraries are, so that it can load the correct copies--otherwise, it may try to load the host's libraries. GDB has two variables to specify the search directories for target libraries.
GDB allows you to put a program's debugging information in a file separate from the executable itself, in a way that allows GDB to find and load the debugging information automatically.
Since debugging information can be very large -- sometimes larger than the executable code itself -- some systems distribute debugging information for their executables in separate files, which users can install only when they need to debug a problem.
If an executable's debugging information has been extracted to a separate file, the executable should contain a debug link giving the name of the debugging information file with no directory components , and a checksum of its contents. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Linked 2.
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