[Qemu-devel] [RFC PATCH] osdep.h: Prohibit disabling assert() in supported builds

[Eric Blake <eblake@redhat.com>]

We already have several files that knowingly require assert()
to work.  While we do NOT want to encourage the use of
'assert(side-effects)' (that is a bad practice that prevents
copy-and-paste of code to other projects that CAN disable
assertions; plus it costs unnecessary reviewer mental cycles
to remember our project policy on crippling asserts), we DO
want to send a message that anyone that disables assertions
has to tweak code in order to compile, making it obvious that
we are not going to support their efforts.

Signed-off-by: Eric Blake <eblake@redhat.com>
---

First mentioned as an idea here:
http://lists.nongnu.org/archive/html/qemu-devel/2017-07/msg06084.html
but I'm titling this RFC as I'm not 100% convinced we want to make
it a project-wide, rather than a per-file decision.

 include/qemu/osdep.h | 12 ++++++++++++
 hw/scsi/mptsas.c     |  4 ----
 hw/virtio/virtio.c   |  4 ----
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 6855b94bbf..9e745a8af9 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -107,6 +107,18 @@ extern int daemon(int, int);
 #include "glib-compat.h"
 #include "qemu/typedefs.h"

+/*
+ * We have a lot of unaudited code that will fail in strange ways if
+ * you disable assertions at compile-time.  You are on your own if
+ * you cripple these safety-checks.
+ */
+#ifdef NDEBUG
+#error building with NDEBUG is not supported
+#endif
+#ifdef G_DISABLE_ASSERT
+#error building with G_DISABLE_ASSERT is not supported
+#endif
+
 #ifndef O_LARGEFILE
 #define O_LARGEFILE 0
 #endif
diff --git a/hw/scsi/mptsas.c b/hw/scsi/mptsas.c
index 765ab53c34..3b93f12cdb 100644
--- a/hw/scsi/mptsas.c
+++ b/hw/scsi/mptsas.c
@@ -1236,11 +1236,7 @@ static void *mptsas_load_request(QEMUFile *f, SCSIRequest *sreq)
     n = qemu_get_be32(f);
     /* TODO: add a way for SCSIBusInfo's load_request to fail,
      * and fail migration instead of asserting here.
-     * When we do, we might be able to re-enable NDEBUG below.
      */
-#ifdef NDEBUG
-#error building with NDEBUG is not supported
-#endif
     assert(n >= 0);

     pci_dma_sglist_init(&req->qsg, pci, n);
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 464947f76d..2778adabcc 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1025,11 +1025,7 @@ void *qemu_get_virtqueue_element(VirtIODevice *vdev, QEMUFile *f, size_t sz)

     /* TODO: teach all callers that this can fail, and return failure instead
      * of asserting here.
-     * When we do, we might be able to re-enable NDEBUG below.
      */
-#ifdef NDEBUG
-#error building with NDEBUG is not supported
-#endif
     assert(ARRAY_SIZE(data.in_addr) >= data.in_num);
     assert(ARRAY_SIZE(data.out_addr) >= data.out_num);

-- 
2.13.5