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From: Philip Semanchuk <philip@semanchuk.com>
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Subject: Adding printf() to observe semaphore behavior?
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Date: Mon, 22 Feb 2016 21:01:46 -0500
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Hi all,
I=E2=80=99m trying to debug a potential kernel problem with POSIX =
semaphores. I=E2=80=99m trying to build a custom kernel with some added =
printf() statements and I=E2=80=99m not seeing any output, neither to =
/var/log/messages nor to the console. I would appreciate any help at =
getting the kernel to talk to me.=20

Here=E2=80=99s what I=E2=80=99ve already done on my PC BSD 10.2 running =
inside a VM =E2=80=94 =20
- Downloaded the source to /usr/src
- Added a printf(=E2=80=9CHello world\n=E2=80=9D) in each implementation =
of sem_open() (both in lib/libc/gen/sem.c and sem_new.c) and one inside =
the implementation of ksem_open() (in sys/kern/uipc_sem.c) for good =
measure. I did not #include <stdio.h> which I=E2=80=99ve read is the =
correct thing to do when one wants to use the kernel=E2=80=99s printf().=20=

- cd /usr/src
- sudo make buildkernel=20
- sudo make installkernel
- reboot
- Create a POSIX semaphore. It works, but I don=E2=80=99t see my =
=E2=80=9CHello world=E2=80=9D message.

Any suggestions on what I=E2=80=99m doing wrong would be appreciated.

Thanks
Philip