[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH V5 00/22] IOREQ feature (+ virtio-mmio) on Arm
On 27.01.2021 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: >>>>>> >>>>>> https://gitlab.com/xen-project/patchew/xen/-/pipelines/246632953 >>>>>> https://gitlab.com/xen-project/patchew/xen/-/jobs/985455044 >>>>> 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 >> parallel. >> >>>>> 'do_memory_op': >>>>> memory.c:1210:18: error: may be used uninitialized in this function >>>>> [-Werror=maybe-uninitialized] >>>>> 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 >> this >> >> default: >> memset(mfn_list, ~0, sizeof(mfn_list)); >> rc = -EOPNOTSUPP; >> break; >> >> 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). Jan
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