compute/fix sum-array-bugs/seg-fault Makefile

[razvang0307]

Add -pthread to LDFLAGS when compiling using <pthread.h>.

[teodutu]

Thanks @razvang0307. I made an inline suggestion, but before addressing that, please tell why this is needed. More recent GCC versions (11 and above for sure, maybe even lower) link lpthread by default.

Does linking cause errors on your system? If so, what GCC and linker versions are you using? Run gcc --version and ld --version and paste the first line of the outputs here.

[razvang0307]

Hello.

Does linking cause errors on your system? If so, what GCC and linker versions are you using? Run gcc --version and ld --version and paste the first line of the outputs here.

gcc: gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
ld: GNU ld (GNU Binutils for Ubuntu) 2.34

Attempting to run make in the directory outputs the following error:

/usr/bin/ld: sum_array_threads.o: in function `main':
/home/student/git/operating-systems/content/chapters/compute/lab/support/sum-array-bugs/seg-fault/sum_array_threads.c:97: undefined reference to `pthread_create'
/usr/bin/ld: /home/student/git/operating-systems/content/chapters/compute/lab/support/sum-array-bugs/seg-fault/sum_array_threads.c:105: undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
make: *** [<builtin>: sum_array_threads] Error 1

The same happens if when appending -lpthread to LDFLAGS, however both -lpthread and -pthread seem to work for LDLIBS.

The environment in which I worked/tested was the qcow2/ARM virtual machine), which was posted on Teams as an answer to the first question on the "Technical Support" channel of the Operating Systems team, emulated via qemu on a native Linux computer.

I don't see any reason for the Makefile to be dependant on what gcc version you have, and there would be no harm in ensuring that the lpthread is linked by default.

[teodutu]

I don't see any reason for the Makefile to be dependant on what gcc version you have, and there would be no harm in ensuring that the lpthread is linked by default.

Yup, you're right. And thanks for the info about your system, now it makes more sense.

To merge this, please squash the 2 commits and then add a summary of the problem that this commit is solving to the commit description (such as "GCC 9.3 doesn't link against libpthread by default, so setting LDLIBS accordingly is required").

To do so, pull the latest commit to your local branch with git pull, then run git rebase -i HEAD~2. This will open a menu with the latest 2 commits. Change the word pick in front of the second one to s (from "squash") and then save and exit. You will be prompted to rewrite the first commit message. Add the description I mentioned above, keep the Signed-off-by line, and then save and exit again. After this, run git push -f to update the remote repo and it should be good to go.

[razvang0307]

The commits have been squashed, thank you for providing the necessary commands and for guiding me through this process.