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Re: [libvirt] portability issue on Centos 6.0



On Tue, Aug 16, 2011 at 08:26:02AM -0600, Eric Blake wrote:
> 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?

  Sorry for reporting late, I had forgotten about the issue, but let's
  try to fix it :-)

libvirt:~ -> rpm -qil systemtap-sdt-devel-1.2-9.el6.x86_64
...
/usr/bin/dtrace
/usr/include/sys/sdt.h
libvirt:~ ->

> >
> >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, ...)                              \

  Yes that fixes it for me (but I didn't try to do much more than
make and make check), I had to rebase the diff slightly as follow,

  thanks, ACK !

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/
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, ...)                              \

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