[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH V5 00/22] IOREQ feature (+ virtio-mmio) on Arm

On 27.01.21 13:22, Jan Beulich wrote:

Hi Jan

On 27.01.2021 12:15, Oleksandr wrote:
On 27.01.21 12:51, Jan Beulich wrote:
On 27.01.2021 11:13, Oleksandr wrote:
On 26.01.21 02:14, Oleksandr wrote:
On 26.01.21 01:20, Julien Grall wrote:
On Mon, 25 Jan 2021 at 20:56, Stefano Stabellini
<sstabellini@xxxxxxxxxx> wrote:
This seems to be an arm randconfig failure:

Thanks! The error is:

#'target_mem_ref' not supported by expression#'memory.c: In function
Btw, I found the first part of this line pretty confusing, to a
degree that when seeing it initially I thought this must be some
odd tool producing the odd error. But perhaps this is just
unfortunate output ordering from different tools running in

memory.c:1210:18: error:  may be used uninitialized in this function
    1210 |             rc = set_foreign_p2m_entry(currd, d, gfn_list[i],
         | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    1211 | _mfn(mfn_list[i]));
         | ~~~~~~~~~~~~~~~~~~

I found a few references online of the error message, but it is not
clear what it means. From a quick look at Oleksandr's branch, I also
can't spot anything unitialized. Any ideas?
It seems that error happens if *both* CONFIG_GRANT_TABLE and
CONFIG_IOREQ_SERVER are disabled. Looks like that mfn_list is
initialized either in acquire_grant_table() or in acquire_ioreq_server().
If these options disabled then corresponding helpers are just stubs,
so indeed that mfn_list gets uninitialized. But, I am not sure why gcc
complains about it as set_foreign_p2m_entry() is *not* going to be
called in that case???
This weird build error goes away if I simply add:

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 33296e6..d1bd57b 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1136,7 +1136,7 @@ static int acquire_resource(
         * moment since they are small, but if they need to grow in future
         * use-cases then per-CPU arrays or heap allocations may be required.
-    xen_pfn_t mfn_list[32];
+    xen_pfn_t mfn_list[32] = {0};
        int rc;

        if ( !arch_acquire_resource_check(currd) )

Shall I make the corresponding patch?
I'd prefer if we could find another solution, avoiding this
pointless writing of 256 bytes of zeros (and really to be on the
safe side I think it should rather be ~0 that gets put in there).
Could you check whether clearing the array along the lines of

          memset(mfn_list, ~0, sizeof(mfn_list));
          rc = -EOPNOTSUPP;

helps (avoiding the writes in all normal cases)?
Yes, this helps (at least in my environment):

aarch64-poky-linux-gcc v8.2
Good. I'd be okay if you folded this in (plus a comment of
course), but others may have different views, not the least as
this is only papering over the issue (yet an issue that's not
ours, but the compiler's).

Great, I will wait a bit and if there are no objections I will fold this in.


Oleksandr Tyshchenko



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.