Comment 77 for bug 1847361

The config is enabled in the right build, but I'm not seeing the new lines passed in the debugger, could be just optimization but it is suspicious.

Poking at the build dir we also see:
  qemu-build/config-host.mak:58:CONFIG_MODULE_UPGRADES=y

If we render the preprocessor step into a file all looks good still:
    char *version_dir;
    char *dirs[4];
...
    version_dir = g_strcanon(g_strdup("(Debian 1:2.11+dfsg-1ubuntu7.24)"),
                             "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "abcdefghijklmnopqrstuvwxyz" "0123456789" "+-.~",
                             '_');
    dirs[i++] = g_strdup_printf("/var/run/qemu/%s", version_dir);

That only is in when the config option was considered correctly.

Some twists later I got the debugging corrected.
Now I see
(gdb) p version_dir
$14 = 0x55bfc6f31880 "_Debian_1_2.11+dfsg-1ubuntu7.24_"
Which ends up as:
$22 = {0x55bfc5bccfa0 "/usr/lib/x86_64-linux-gnu/qemu", 0x55bfc5dc4710 "/usr/bin/..", 0x55bfc5cf1840 "/usr/bin", 0x55bfc5ea98d0 "/var/run/qemu/_Debian_1_2.11+dfsg-1ubuntu7.24_"}

Do mind the leading and trailing underscores.

That is due to the version in Bionic still having:
config-host.mak:52:PKGVERSION= (Debian 1:2.11+dfsg-1ubuntu7.24)
qemu-version.h:1:#define QEMU_PKGVERSION "(Debian 1:2.11+dfsg-1ubuntu7.24)"

And with that we get as expected:
7f70d74d6000-7f70d74d7000 rw-p 00008000 00:4d 204 /run/qemu/_Debian_1_2.11+dfsg-1ubuntu7.24_/block-iscsi.so
and
7f70d6ea0000-7f70d6ea1000 r--p 00004000 00:4d 203 /run/qemu/_Debian_1_2.11+dfsg-1ubuntu7.24_/block-curl.so

So the backport needs to adapt in the maintscripts to reflect that older behavior of having the enclosing brackets as part of the version string.
Now that the issue is understood the fix is trivial - I'll do a test run of a PPA and upload to -unapproved later on.