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vgdb: "No such file or directory" shared memory file when running in process network namespace

I'm trying to debug a program using Valgrind and GDB. To run the program in my test suite it has to be run within a network namespace (using ip netns exec <namespace>), as it has to simulate different network connections. To run the program I want to debug I run the following command:

ip netns exec my-ns valgrind --leak-check=full --vgdb=yes --vgdb-error=0 <program> <args>

This runs without any problems, but when I try to connect using GDB I get the following error:

(gdb) target remote | vgdb
Remote debugging using | vgdb
syscall failed: No such file or directory
error opening /tmp/vgdb-pipe-shared-mem-vgdb-<pid>-by-root-on-??? shared memory file
Remote communication error. Target disconnected.: Connection reset by peer.

I've tried running the GDB command both within the namespace and without as follows, and they both give me the same error:

gdb <binary>
ip netns exec my-ns gdb <binary>

When looking at the files generated by VGDB in /tmp I find the following:

prw------- 1 root root  0 Dec 20 08:31 vgdb-pipe-from-vgdb-to-<pid>-by-root-on-<hostname>
-rw------- 1 root root 48 Dec 20 08:31 vgdb-pipe-shared-mem-vgdb-<pid>-by-root-on-<hostname>
prw------- 1 root root  0 Dec 20 08:31 vgdb-pipe-to-vgdb-from-<pid>-by-root-on-<hostname>

I am running all commands as root, so there should be no permissions problems here either. I have also verified that there is no problem running the same process without the process namespace - although then I am unable to perform my tests. Also, curiously enough, when I run without ip netns exec I get the following files in /tmp, not seeming to pick up my hostname:

prw------- 1 root root  0 Dec 20 08:44 'vgdb-pipe-from-vgdb-to-<pid>-by-root-on-???'
-rw------- 1 root root 48 Dec 20 08:44 'vgdb-pipe-shared-mem-vgdb-<pid>-by-root-on-???'
prw------- 1 root root  0 Dec 20 08:44 'vgdb-pipe-to-vgdb-from-<pid>-by-root-on-???'

I appreciate your replies.

Solution

  • In order to determine the hostname, Valgrind and vgdb use the following rules

    1. Uses the HOST environment variable
    2. Uses the HOSTNAME environment variable
    3. If neither of the above are set, uses "???"
    4. If one of the environment variables was set and the hostname contains '/' then again "???" is used.

    I don't know how ip netns exec affects such variables. Maybe you can use a script that sets HOSTNAME to whatever Valgrind is seeing and then starts gdb.