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build: work around older systemtap header

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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.
This commit is contained in:
Eric Blake 2011-07-01 12:33:50 -06:00
parent baac9c37d7
commit 6611d9ebcc
1 changed files with 31 additions and 1 deletions
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32
daemon/libvirtd.h
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@ -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, ...) \