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RE: Build problems in kdd.c with xen-4.14.0-rc4

  • To: paul@xxxxxxx
  • From: Michael Young <m.a.young@xxxxxxxxxxxx>
  • Date: Fri, 3 Jul 2020 10:48:57 +0100 (BST)
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, 'Tim Deegan' <tim@xxxxxxx>
  • Delivery-date: Fri, 03 Jul 2020 09:49:13 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On Fri, 3 Jul 2020, Paul Durrant wrote:

-----Original Message-----
From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Michael 
Sent: 30 June 2020 23:22
To: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Tim Deegan <tim@xxxxxxx>
Subject: Build problems in kdd.c with xen-4.14.0-rc4

I get the following errors when trying to build xen-4.14.0-rc4

kdd.c: In function 'kdd_tx':
kdd.c:754:15: error: array subscript 16 is above array bounds of 'uint8_t[16]' 
{aka 'unsigned
char[16]'} [-Werror=array-bounds]
   754 |         s->txb[len++] = 0xaa;
       |         ~~~~~~^~~~~~~
kdd.c:82:17: note: while referencing 'txb'
    82 |         uint8_t txb[sizeof (kdd_hdr)];           /* Marshalling area 
for tx */
       |                 ^~~
kdd.c: In function 'kdd_break':
kdd.c:819:19: error: array subscript 16 is above array bounds of 'uint8_t[16]' 
{aka 'unsigned
char[16]'} [-Werror=array-bounds]
   819 |             s->txb[sizeof (kdd_hdr) + i] = i;
       |             ~~~~~~^~~~~~~~~~~~~~~~~~~~~~
kdd.c:82:17: note: while referencing 'txb'
    82 |         uint8_t txb[sizeof (kdd_hdr)];           /* Marshalling area 
for tx */
       |                 ^~~
In file included from /usr/include/stdio.h:867,
                  from kdd.c:36:
In function 'vsnprintf',
     inlined from 'kdd_send_string' at kdd.c:791:11:
/usr/include/bits/stdio2.h:80:10: error: '__builtin___vsnprintf_chk' specified 
bound 65519 exceeds
destination size 0 [-Werror=stringop-overflow=]
    80 |   return __builtin___vsnprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    81 |         __bos (__s), __fmt, __ap);
       |         ~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[4]: *** 
kdd.o] Error 1

The first two array-bounds errors seem to be a result of the

kdd: stop using [0] arrays to access packet contents

patch at

which reduced the size of txb from
sizeof (kdd_hdr) + 65536
sizeof (kdd_hdr)
which means the code now tries to write beyond the end of txb in both

Sorry not to get back to you sooner. Which compiler are you using?


This was with gcc-10.1.1-1.fc32.x86_64
Full build logs are (at the moment) at https://download.copr.fedorainfracloud.org/results/myoung/xentest/fedora-32-x86_64/01515056-xen/

        Michael Young



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