libqtest: refuse QTEST_QEMU_BINARY=qemu-kvm

Some downstreams rename the QEMU binary to "qemu-kvm". This breaks
qtest_get_arch(), which attempts to parse the target architecture from
the QTEST_QEMU_BINARY environment variable.

Print an error instead of returning the architecture "kvm". Things fail
in weird ways when the architecture string is bogus.

Arguably qtests should always be run in a build directory instead of
against an installed QEMU. In any case, printing a clear error when this
happens is helpful.

Since this is an error that is triggered by the user and not a test
failure, use exit(1) instead of abort(). Change the existing abort()
call in qtest_get_arch() to exit(1) too for the same reason and to be
consistent.

Reported-by: Qin Wang <qinwang@rehdat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Cc: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20210412143050.725918-1-stefanha@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/qtest/libqtest.c

@@ -907,7 +907,14 @@ const char *qtest_get_arch(void)
 
     if (!end) {
         fprintf(stderr, "Can't determine architecture from binary name.\n");
-        abort();
+        exit(1);
+    }
+
+    if (!strstr(qemu, "-system-")) {
+        fprintf(stderr, "QTEST_QEMU_BINARY must end with *-system-<arch> "
+                "where 'arch' is the target\narchitecture (x86_64, aarch64, "
+                "etc).\n");
+        exit(1);
     }
 
     return end + 1;