Bug 999419

Description of problem:

Libvirt uses systemtaps' dtrace compatibility tool to generate the probe header file definitions based on a dtrace provider script.

When we compile Libvirt with CLang the dtrace / systemtap probes cause a slew of compiler errors.

I'm unclear whether the fault is with systemtap generating non-portable code, or with clang not honouring some part of the C spec. Picking systemtap to file the bug though, since even if clang doesn't honour the C spec in this area, I think it is still desirable for systemtap to generate working code for clang.

The following steps demonstrate the problem on Fedora 19 x86_64

$ cat sdt.c
#include <sys/sdt.h>

#include "sdt.h"

int foo(void)
{
  DEMO_FOO();
  return 0;
}


int main(void)
{
  return foo();
}


$ cat sdt.d

provider demo {
	 probe foo();
};


$ dtrace -o sdt.h -h  -s sdt.d
$ clang -o sdt sdt.c
sdt.c:7:3: error: unknown flag
  DEMO_FOO();
  ^
./sdt.h:19:20: note: expanded from macro 'DEMO_FOO'
#define DEMO_FOO() \
                   ^
/usr/include/sys/sdt.h:362:3: note: expanded from macro '\
DTRACE_PROBE'
  STAP_PROBE(provider,probe)
  ^
/usr/include/sys/sdt.h:254:3: note: expanded from macro 'STAP_PROBE'
  _SDT_PROBE(provider, name, 0, ())
  ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/usr/include/sys/sdt.h:43:31: note: expanded from macro '_SDT_ASM_3'
# define _SDT_ASM_3(a, b, c)            _SDT_S(a) "," _SDT_S(b) "," \
                                        ^
/usr/include/sys/sdt.h:40:22: note: expanded from macro '_SDT_S'
# define _SDT_S(x)                      #x
                                        ^
<scratch space>:4:2: note: expanded from here
".pushsection .note.stapsdt"
 ^
<inline asm>:2:31: note: instantiated into assembly here
.pushsection .note.stapsdt,"?","note"
                              ^
sdt.c:7:3: error: .popsection without corresponding .pushsection
  DEMO_FOO();
  ^
./sdt.h:19:20: note: expanded from macro 'DEMO_FOO'
#define DEMO_FOO() \
                   ^
/usr/include/sys/sdt.h:362:3: note: expanded from macro '\
DTRACE_PROBE'
  STAP_PROBE(provider,probe)
  ^
/usr/include/sys/sdt.h:254:3: note: expanded from macro 'STAP_PROBE'
  _SDT_PROBE(provider, name, 0, ())
  ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/usr/include/sys/sdt.h:41:26: note: expanded from macro '_SDT_ASM_1'
# define _SDT_ASM_1(x)                  _SDT_S(x) "\n"
                                        ^
/usr/include/sys/sdt.h:40:22: note: expanded from macro '_SDT_S'
# define _SDT_S(x)                      #x
                                        ^
<scratch space>:24:2: note: expanded from here
".popsection"
 ^
<inline asm>:14:12: note: instantiated into assembly here
.popsection
           ^
sdt.c:7:3: error: expected '@' or '%' before type
  DEMO_FOO();
  ^
./sdt.h:19:20: note: expanded from macro 'DEMO_FOO'
#define DEMO_FOO() \
                   ^
/usr/include/sys/sdt.h:362:3: note: expanded from macro '\
DTRACE_PROBE'
  STAP_PROBE(provider,probe)
  ^
/usr/include/sys/sdt.h:254:3: note: expanded from macro 'STAP_PROBE'
  _SDT_PROBE(provider, name, 0, ())
  ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/usr/include/sys/sdt.h:45:36: note: expanded from macro '_SDT_ASM_5'
# define _SDT_ASM_5(a, b, c, d, e)      _SDT_S(a) "," _SDT_S(b) "," \
                                        ^
/usr/include/sys/sdt.h:40:22: note: expanded from macro '_SDT_S'
# define _SDT_S(x)                      #x
                                        ^
<scratch space>:27:2: note: expanded from here
".pushsection .stapsdt.base"
 ^
<inline asm>:2:33: note: instantiated into assembly here
.pushsection .stapsdt.base,"aG","progbits",.stapsdt.base,comdat
                                ^
sdt.c:7:3: error: .popsection without corresponding .pushsection
  DEMO_FOO();
  ^
./sdt.h:19:20: note: expanded from macro 'DEMO_FOO'
#define DEMO_FOO() \
                   ^
/usr/include/sys/sdt.h:362:3: note: expanded from macro '\
DTRACE_PROBE'
  STAP_PROBE(provider,probe)
  ^
/usr/include/sys/sdt.h:254:3: note: expanded from macro 'STAP_PROBE'
  _SDT_PROBE(provider, name, 0, ())
  ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/usr/include/sys/sdt.h:41:26: note: expanded from macro '_SDT_ASM_1'
# define _SDT_ASM_1(x)                  _SDT_S(x) "\n"
                                        ^
/usr/include/sys/sdt.h:40:22: note: expanded from macro '_SDT_S'
# define _SDT_S(x)                      #x
                                        ^
<scratch space>:37:2: note: expanded from here
".popsection"
 ^
<inline asm>:7:12: note: instantiated into assembly here
.popsection
           ^
4 errors generated.


Gcc by comparison works as expected

$ gcc -o sdt sdt.c
...no errors...

Systemtap support is the only remaining blocker to building a fully featured libvirt with clang.

Version-Release number of selected component (if applicable):
systemtap-sdt-devel-2.3-1.fc19.x86_64
clang-3.3-0.6.rc3.fc19.x86_64