Re: [libvirt] portability issue on Centos 6.0

On 08/16/2011 03:57 AM, Daniel Veillard wrote: What version of systemtap headers are installed? 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(a)redhat.com&gt; 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(a)redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org