Re: [PATCH] util: In ASSERT(), use "fprintf(stderr, ...)" rather than err(...)

[Laurent Vivier <lvivier@redhat.com>]

On 05/08/2024 16:34, Stefano Brivio wrote:
> On Mon,  5 Aug 2024 16:10:27 +0200
> Laurent Vivier <lvivier@redhat.com> wrote:
> 
>> We use our own implementation of assert() because the glic implementation
>> uses syscalls that aren't in our seccomp filter, see 7a8ed9459dfe
>> ("Make assertions actually useful"). And we replaced it by an err(),
>> followed by an abort() (that is also catched by seccomp).
>> We don't have a coredump or a backtrace but we have at least the
>> error message... only if logging is enabled.
> 
> ...wait, err() should always end up somewhere (syslog, log file, or
> stderr). If you pick stderr, and we closed stderr, then the error will
> not be reported anywhere (or, possibly worse, on a socket that happens
> to have number 2).
> 
> In which case are you losing messages?
> 

Try something:

diff --git a/udp.c b/udp.c
index a92014806a73..7e179d3b863b 100644
--- a/udp.c
+++ b/udp.c
@@ -707,6 +707,8 @@ void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
         if ((n = udp_sock_recv(c, ref.fd, events, mmh_recv)) <= 0)
                 return;

+       ASSERT(0);
+
         /* We divide datagrams into batches based on how we need to send them,
          * determined by udp_meta[i].tosidx.  To avoid either two passes through
          * the array, or recalculating tosidx for a single entry, we have to

And then generate some UDP traffic.

This exits only with:

Bad system call

Oh, wait, I can see the error in the syslog... but it's not very intuitive as we have the 
"Bad system call" displayed in the terminal.

So, ignore my patch.

Laurent