This problem comes from our PAPI list, but is a pfmlib problem when
compiling with
IBM XL C/C++. I investigated it.
First, this is a real problem that prevents creating libpfm.so.
Second, I found no clean workaround (other than using gcc instead of xlC),
but there is a way to create a functional lib using xlC.
The line of code that causes the error in pfmlib.h:29 is
#pragma GCC visibility push (default)
The error report is as follows;
The attribute " __attribute__((visibility("default")))" is not a valid type
attribute. The attribute is ignored. The error number given by xlC is
1540-0081. The problem was reported for xlC 16.01,
I did not have that and tested on our latest beta version, xlC
16.1.1-beta6.
Experiments show the compiler will not recognize any valid attribute. Those
are
[default, protected, hidden, internal], they all get 1540-0081.
This is an error that does not occur when compiling with GCC; it interprets
the lines correctly, and they have the desired effect (making function
names in the library hidden or visible when using the linux "nm" utility,
specifically "nm -C -D libpfm4.so").
Searching the web for ways to deal with error 1540-0081, we found it has
been produced by a compiler bug in another problem. For those, IBM says
compile with the -qsuppress=1540-0081 flag. We tried that here; and
although the xlC compiler accepted the flag, it did not fix our problem.
Failing that, the only way I found to produce a usable lib was by deleting
the #pragmas and changing the compile flag -fvisibility.
There were three header files to modify:
perf_event.h, pfmlib.h, pfmlib_perf_event.h. There are two lines in each
to comment out; a ;'push' and a 'pop'. This is the grep I used to find them:
~/papi/src/libpfm4$ grep "#pragma GCC visibility" -H -n -r --include="*"
The following is the result:
include/perfmon/perf_event.h:25:#pragma GCC visibility push(default)
include/perfmon/perf_event.h:618:#pragma GCC visibility pop
include/perfmon/pfmlib.h:29:#pragma GCC visibility push(default)
include/perfmon/pfmlib.h:787:#pragma GCC visibility pop
include/perfmon/pfmlib_perf_event.h:28:#pragma GCC visibility push(default)
include/perfmon/pfmlib_perf_event.h:66:#pragma GCC visibility pop
I also modified the pfmlib4/lib/Makefile, line 36 reads:
CFLAGS+=-D_REENTRANT -I. -fvisibility=hidden
and the 'hidden' needs to be changed to 'default': We can't make every
function hidden!
CFLAGS+=-D_REENTRANT -I. -fvisibility=default
This had no compile errors using xlC, and produced a libpfm.so with a lot
of
routines visible that are not visible when compiled with GCC, but all the
ones
GCC made visible are also visible in the xlC versionof the lib.
The size of the xlC produced lib is virtually the same as the GCC lib.
(gcc=1,377,120 bytes, xlC=1,377,680 bytes. 560 bytes more).
I have no prior experience with xlC, so there may be a more elegant method
of doing this. However, I believe the syntax of the #pragma's is correct,
and
since they work as written for gcc, I suspect an xlC compiler error. It
might
not exist in other versions of xlC, or may be corrected in future versions.
Tony C.
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