How to fix GDB not finding file: "../sysdeps/unix/sysv/linux/raise.c:50"

Question

We're learning to use GDB in my Computer Architecture class. To do this we do most of our work by using SSH to connect to a raspberry pi. When running GDB on some code he gave us to debug though it ends with an error message on how it can't find raise.c

I've tried:

installing libc6, libc6-dbg (says they're already up-to-date)

apt-get source glibc (gives me: "You must put some 'source' URIs in your sources.list")

https://stackoverflow.com/a/48287761/12015458 (apt source returns same thing as the apt-get source above, the "find $PWD" command the user gave returns nothing)

I've tried looking for it manually where told it may be? (/lib/libc doesn't exist for me)

This is the code he gave us to try debugging on GDB:

#include <stdio.h>
main()
{
        int x,y;
        y=54389;
        for (x=10; x>=0; x--)
        y=y/x;
        printf("%d\n",y);
}

However, whenever I run the code in GDB I get the following error:

Program received signal SIGFPE, Arithmetic exception.
__GI_raise (sig=8) at ../sysdeps/unix/sysv/linux/raise.c:50
50      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.

I asked him about it and he didn't really have any ideas on how to fix it.

Answer 1

From a practical standpoint the other answer is correct, but if you do want the libc sources:

apt-get source is the right way to get the sources of libc, but yes, you do need to have source repositories configured in /etc/apt/sources.list.

If you're using Ubuntu, see the deb-src lines in https://help.ubuntu.com/community/Repositories/CommandLine

For debian, see https://wiki.debian.org/SourcesList#Example_sources.list

Then apt-get source should work. Remember to tell GDB where those sources are using the "directory" command.

Answer 2

It does not really matter that the source for raise() is not found. It would only show you the line where the exception is finally raised, but not the place where the error is triggered.

Run the erroneous program again in GDB. And when the exception is raised, investigate the call stack and the stackframes with GBDs commands. This is the point in your task, so I won't give you more than this hint.

If you're clever you can see the error in the given source just by looking at it. ;-)

When GDB does not know any symbol, you need to compile with the option -g to get debugger support.

EDIT

Now on a Windows system this is my log (please excuse the colouring, I didn't found a language selector for pure text):

D:\tmp\StackOverflow\so_027 > type crash1.c
#include <stdio.h>
main()
{
        int x,y;
        y=54389;
        for (x=10; x>=0; x--)
        y=y/x;
        printf("%d\n",y);
}

D:\tmp\StackOverflow\so_027 > gcc crash1.c -g -o crash1.out
crash1.c:2:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main()
 ^~~~

D:\tmp\StackOverflow\so_027 > dir
[...cut...]
04.09.2019  08:33               144 crash1.c
04.09.2019  08:40            54.716 crash1.out

D:\tmp\StackOverflow\so_027 > gdb crash1.out
GNU gdb (GDB) 8.1
[...cut...]
This GDB was configured as "x86_64-w64-mingw32".
[...cut...]
Reading symbols from crash1.out...done.
(gdb) run
Starting program: D:\tmp\StackOverflow\so_027\crash1.out
[New Thread 4520.0x28b8]
[New Thread 4520.0x33f0]

Thread 1 received signal SIGFPE, Arithmetic exception.
0x0000000000401571 in main () at crash1.c:7
7               y=y/x;
(gdb) backtrace
#0  0x0000000000401571 in main () at crash1.c:7
(gdb) help stack
Examining the stack.
The stack is made up of stack frames.  Gdb assigns numbers to stack frames
counting from zero for the innermost (currently executing) frame.

At any time gdb identifies one frame as the "selected" frame.
Variable lookups are done with respect to the selected frame.
When the program being debugged stops, gdb selects the innermost frame.
The commands below can be used to select other frames by number or address.

List of commands:

backtrace -- Print backtrace of all stack frames
bt -- Print backtrace of all stack frames
down -- Select and print stack frame called by this one
frame -- Select and print a stack frame
return -- Make selected stack frame return to its caller
select-frame -- Select a stack frame without printing anything
up -- Select and print stack frame that called this one

Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.
(gdb) next

Thread 1 received signal SIGFPE, Arithmetic exception.
0x0000000000401571 in main () at crash1.c:7
7               y=y/x;
(gdb) next
[Inferior 1 (process 4520) exited with code 030000000224]
(gdb) next
The program is not being run.
(gdb) quit

D:\tmp\StackOverflow\so_027 >

Well, it marks directly the erroneous source line. That is different to your environment as you use a Raspi. However, it shows you some GDB commands to try.

Concerning your video:

• It is clear that inside raise() you can't access x. That's why GDB moans about it.
• If an exception is raised usually the program is about to quit. So there is no value in stepping forward.
• Instead, as shown in my log, use GDB commands to investigate the stack frames. I think this is the issue you are about to learn.

BTW, do you know that you should be able to copy the screen content? This will make reading so much easier for us.