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

[Paul Durrant <xadimgnik@gmail.com>]

> -----Original Message-----
> From: Michael Young <m.a.young@durham.ac.uk>
> Sent: 03 July 2020 10:49
> To: paul@xen.org
> Cc: xen-devel@lists.xenproject.org; 'Tim Deegan' <tim@xen.org>
> Subject: RE: Build problems in kdd.c with xen-4.14.0-rc4
> 
> On Fri, 3 Jul 2020, Paul Durrant wrote:
> 
> >> -----Original Message-----
> >> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf Of Michael Young
> >> Sent: 30 June 2020 23:22
> >> To: xen-devel@lists.xenproject.org
> >> Cc: Tim Deegan <tim@xen.org>
> >> 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]: *** [/builddir/build/BUILD/xen-4.14.0-rc4/tools/debugger/kdd/../../../tools/Rules.mk:216:
> >> 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
> >> http://xenbits.xenproject.org/gitweb/?p=xen.git;a=commit;h=3471cafbdda35eacf04670881dd2aee2558b4f08
> >>
> >> which reduced the size of txb from
> >> sizeof (kdd_hdr) + 65536
> >> to
> >> sizeof (kdd_hdr)
> >> which means the code now tries to write beyond the end of txb in both
> >> cases.
> >>
> >
> > Sorry not to get back to you sooner. Which compiler are you using?
> >
> >  Paul
> 
> 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/
> 

Ok, I have an older compiler. Does this patch fix it for you?

---8<---
diff --git a/tools/debugger/kdd/kdd.c b/tools/debugger/kdd/kdd.c
index 866532f0c7..a7d0976ea4 100644
--- a/tools/debugger/kdd/kdd.c
+++ b/tools/debugger/kdd/kdd.c
@@ -79,11 +79,11 @@ typedef struct {
 /* State of the debugger stub */
 typedef struct {
     union {
-        uint8_t txb[sizeof (kdd_hdr)];           /* Marshalling area for tx */
+        uint8_t txb[sizeof (kdd_pkt)];           /* Marshalling area for tx */
         kdd_pkt txp;                 /* Also readable as a packet structure */
     };
     union {
-        uint8_t rxb[sizeof (kdd_hdr)];           /* Marshalling area for rx */
+        uint8_t rxb[sizeof (kdd_pkt)];           /* Marshalling area for rx */
         kdd_pkt rxp;                 /* Also readable as a packet structure */
     };
     unsigned int cur;       /* Offset into rx where we'll put the next byte */
---8<---

  Paul

>  	Michael Young