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

Re: [libvirt] portability issue on Centos 6.0



On 08/16/2011 03:57 AM, Daniel Veillard wrote:
   I just tred compiling 0.9.4 and git head on Centos 6.0, for the
possible libvirt.org server replacement and it fails in both cases
with:

   CC     libvirtd-remote.o
remote.c: In function 'remoteDispatchAuthPolkit':
remote.c:2161: error: invalid initializer

What version of systemtap headers are installed?


This correspond to the following macro

     PROBE(CLIENT_AUTH_ALLOW, "fd=%d, auth=%d, username=%s",
               virNetServerClientGetFD(client), REMOTE_AUTH_POLKIT,
               ident);

I'm a bit lost how the expansion could lead to this and why, unless the
DTrace support in Centos 6 is slightly different than on RHEL, I will
look but if someone has an idea :-)

This came up previously, and I wrote this RFC patch:
https://www.redhat.com/archives/libvir-list/2011-July/msg00053.html

but no one replied whether we really want it in the tree.

commit c6793e397d0e62e2d00bfa1beb910fd09b254337
Author: Eric Blake <eblake redhat com>
Date:   Fri Jul 1 12:33:50 2011 -0600

    build: work around older systemtap header

    Systemtap 1.2 <sys/sdt.h> tried to expand STAP_PROBE3 into an
    initialization:
      volatile __typeof__(arg) foo = arg;
    but that fails if arg was declared as 'char arg[100]'.
    Rather than make all callers to PROBE deal with the stupidity
    of <sys/sdt.h>, we instead make PROBE cast away the problem.
    Some of this preprocessor abuse copies ideas in src/libvirt.c.

    * daemon/libvirtd.h (PROBE): Add casts to all arguments, using...
    (VIR_ADD_CASTS, VIR_ADD_CAST, VIR_ADD_CAST2, VIR_ADD_CAST3)
    (VIR_ADD_CAST_EXPAND, VIR_ADD_CAST_PASTE, VIR_COUNT_ARGS)
    (VIR_ARG5, PROBE_EXPAND): New macros.
    Reported by Wen Congyang.

diff --git a/daemon/libvirtd.h b/daemon/libvirtd.h
index 6c9b9c3..6d6460e 100644
--- a/daemon/libvirtd.h
+++ b/daemon/libvirtd.h
@@ -44,11 +44,41 @@
 #   define LIBVIRTD_PROBES_H
 #   include "probes.h"
 #  endif /* LIBVIRTD_PROBES_H */
+
+/* Systemtap 1.2 headers have a bug where they cannot handle a
+ * variable declared with array type.  Work around this by casting all
+ * arguments.  This is some gross use of the preprocessor because
+ * PROBE is a var-arg macro, but it is better than the alternative of
+ * making all callers to PROBE have to be aware of the issues.  And
+ * hopefully, if we ever add a call to PROBE with other than 2 or 3
+ * end arguments, you can figure out the pattern to extend this hack.
+ */
+#  define VIR_COUNT_ARGS(...) VIR_ARG5(__VA_ARGS__, 4, 3, 2, 1)
+#  define VIR_ARG5(_1, _2, _3, _4, _5, ...) _5
+# define VIR_ADD_CAST_EXPAND(a, b, ...) VIR_ADD_CAST_PASTE(a, b, __VA_ARGS__)
+#  define VIR_ADD_CAST_PASTE(a, b, ...) a##b(__VA_ARGS__)
+
+/* The double cast is necessary to silence gcc warnings; any pointer
+ * can safely go to intptr_t and back to void *, which collapses
+ * arrays into pointers; while any integer can be widened to intptr_t
+ * then cast to void *.  */
+#  define VIR_ADD_CAST(a) ((void *)(intptr_t)(a))
+#  define VIR_ADD_CAST2(a, b)                           \
+    VIR_ADD_CAST(a), VIR_ADD_CAST(b)
+#  define VIR_ADD_CAST3(a, b, c)                        \
+    VIR_ADD_CAST(a), VIR_ADD_CAST(b), VIR_ADD_CAST(c)
+
+#  define VIR_ADD_CASTS(...)                                            \
+    VIR_ADD_CAST_EXPAND(VIR_ADD_CAST, VIR_COUNT_ARGS(__VA_ARGS__),      \
+                        __VA_ARGS__)
+
+#  define PROBE_EXPAND(NAME, ARGS) NAME(ARGS)
 #  define PROBE(NAME, FMT, ...)                              \
     VIR_DEBUG_INT("trace." __FILE__ , __func__, __LINE__,    \
                   #NAME ": " FMT, __VA_ARGS__);              \
     if (LIBVIRTD_ ## NAME ## _ENABLED()) {                   \
-        LIBVIRTD_ ## NAME(__VA_ARGS__);                      \
+        PROBE_EXPAND(LIBVIRTD_ ## NAME,                      \
+                     VIR_ADD_CASTS(__VA_ARGS__));            \
     }
 # else
 #  define PROBE(NAME, FMT, ...)                              \


--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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