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Subject: Re: [OMPI devel] Warnings from pgcc-13.10
From: Larry Baker (baker_at_[hidden])
Date: 2014-01-17 15:27:22


Paul,

> So, if I follow your report correctly is is probably the "static" (not the "const") property of the string literals' type that leads pgcc to warn. If that is the case, then I agree that this is NOT a warning that is consistent with the C standard's rules for type compatibility. Thus I agree that it is probably a PGI bug.

I had not thought about static causing the problem; I assumed it was the const'ness mismatch. (static is not a valid function prototype argument qualifier, right? static is a storage class, not a type qualifier. Plus, even though the NetCDF code says it returns a static*, I don't think there is such a thing. I've since read up on C string literals more carefully, and I found that the standard says they have static storage class, i.e., a pointer to a string literal can be returned by a function. And, literal strings do not have the const type qualifier. A mistake, in my view.)

Can you point me at a tarball I can download with the code that gives these warnings, and maybe the configure args you used? I can try to figure out if it is the same problem I reported before.

I sent a tickler to ask PGI what the status was of the TPR 17139 assigned to my original report.

Larry Baker
US Geological Survey
650-329-5608
baker_at_[hidden]

On 17 Jan 2014, at 12:04 PM, Paul Hargrove wrote:

> Larry,
>
> So, if I follow your report correctly is is probably the "static" (not the "const") property of the string literals' type that leads pgcc to warn. If that is the case, then I agree that this is NOT a warning that is consistent with the C standard's rules for type compatibility. Thus I agree that it is probably a PGI bug.
>
> Ralph,
>
> If we determine that these warnings are the product of a PGI bug, but one can silence them with a cast, then how do you want to proceed? I can probably sort out all four combinations of static and const qualified char* pretty quickly (once I get the chance).
>
> -Paul
>
>
> On Fri, Jan 17, 2014 at 11:44 AM, Larry Baker <baker_at_[hidden]> wrote:
> Paul,
>
> From what I can see in the arguments to OPAL_OUTPUT_VERBOSE() in line 356 at https://bitbucket.org/ompiteam/ompi-svn-mirror/src/f48eeda443104a64dc89e4f5fab4c940e44d8615/opal/mca/db/hash/db_hash.c, this is the same PGI bug I reported 22 Jul 2010, which was assigned TPR 17139.
>
>
>> Customer information:
>>
>> Larry Baker
>> US Geological Survey
>> 650-329-5608
>> baker_at_[hidden]
>>
>> Product: 2183-WS
>> PIN: 507549
>>
>> Problem description:
>>
>> I am trying to track down the warnings that occur when compiling the UCAR NetCDF package with PGI compilers. I have found a case that gcc does not warn about, but pgcc does. If I understand the code and the C (1990) standard, I think pgcc is complaining too much.
>>
>> You can reproduce the warnings by downloading the UCAR NetCDF source package, netcdf.tar.gz, fromhttp://www.unidata.ucar.edu/software/netcdf/. Assuming you download it to /usr/local/src, here are the commands that illustrate the warnings:
>>
>> # cd /usr/local/src
>> # tar -xzf netcdf.tar.gz
>> # cd netcdf-4.1.1
>> # ./configure >/dev/null 2>&1
>> # cd ncgen
>> # pgcc -DHAVE_CONFIG_H -I. -I.. -I../fortran -I.. -I../libsrc -I../libsrc -g -O2 -tp amd64 -Msignextend -DNO_PGI_OFFSET -c -o genf77.o genf77.c
>> PGC-W-0095-Type cast required for this conversion (genf77.c: 498)
>> PGC-W-0095-Type cast required for this conversion (genf77.c: 511)
>> PGC/x86-64 Linux 10.3-0: compilation completed with warnings
>>
>> To eliminate the warnings, I had to modify the two source lines to cast the result from static const char* f77varncid() as (char *):
>>
>>> /* Use the specialized put_att_XX routines if possible*/
>>> switch (basetype->typ.typecode) {
>>> case NC_BYTE:
>>> case NC_SHORT:
>>> case NC_INT:
>>> case NC_FLOAT:
>>> case NC_DOUBLE:
>>> f77attrify(asym,code);
>>> codedump(code);
>>> bbClear(code);
>>> bbprintf0(stmt,"stat = nf_put_att_%s(ncid, %s, %s, %s, %lu, %sval)\n",
>>> nfstype(basetype->typ.typecode),
>>> (asym->att.var == NULL?"NF_GLOBAL"
>>> :(char *) f77varncid(asym->att.var)), <--- here
>>> f77escapifyname(asym->name),
>>> nftype(basetype->typ.typecode),
>>> len,
>>> ncftype(basetype->typ.typecode));
>>> codedump(stmt);
>>> break;
>>>
>>> case NC_CHAR:
>>> len = bbLength(code);
>>> f77quotestring(code);
>>> bbprintf0(stmt,"stat = nf_put_att_text(ncid, %s, %s, %lu, ",
>>> (asym->att.var == NULL?"NF_GLOBAL"
>>> :(char *)f77varncid(asym->att.var)), <--- and here
>>> f77escapifyname(asym->name),
>>> (len==0?1:len));
>>> codedump(stmt);
>>> codedump(code);
>>> codeline(")");
>>> break;
>>
>> Here is static const char* f77varncid():
>>
>>> /* Compute the name for a given var's id*/
>>> /* Watch out: the result is a static*/
>>> static const char*
>>> f77varncid(Symbol* vsym)
>>> {
>>> const char* tmp1;
>>> char* vartmp;
>>> tmp1 = f77name(vsym);
>>> vartmp = poolalloc(strlen(tmp1)+strlen("_id")+1);
>>> strcpy(vartmp,tmp1);
>>> strcat(vartmp,"_id");
>>> return vartmp;
>>> }
>>
>> There are other lines in genf77.c that use f77varncid() in a print statement, so the warnings do not occur every time f77varncid() provides a string for %s:
>>
>>> if (nvars > 0) {
>>> f77skip();
>>> f77comment("variable ids");
>>> for(ivar = 0; ivar < nvars; ivar++) {
>>> Symbol* vsym = (Symbol*)listget(vardefs,ivar);
>>> bbprintf0(stmt,"integer %s;\n", f77varncid(vsym));
>>> codedump(stmt);
>>> }
>>
>> The warnings occur in the only two instances where f77varncid() is used in a conditional expression. In both cases, the second operand is a literal string, e.g., "NF_GLOBAL". I would have thought that a (static const char*) and a string literal would be compatible types. I experimented with a (const char *) cast instead of a (char *) cast, but that does not work. I think it should.
>>
>> I admit, I have an old copy of the C standard — from 1990. But, here's my interpretation of what it says about this:
>>
>> • 6.1.4 String literals, says string literals are converted to an array of type char. If the program attempts to modify a string literal, the behavior is undefined. It does not say that the type has the const type qualifier (though, you would think it should).
>>
>> • 6.3.15 Conditional operator, says if the second and third operands are pointers ..., the result type is a pointer to a type qualified with all the type qualifiers of the types pointed-to by both operands.
>>
>> This would seem to explain the warning message, since the string literal is (char *) and f77varncid() is (const char *). However, 6.3.15 goes on to say:
>>
>> Furthermore, if both operands are pointers to ... differently qualified versions of a compatible type, the result has the composite type.
>>
>> Which leads me to believe you are allowed to mix const and non-const versions of a compatible type.
>>
>> Lastly:
>>
>> • 6.5.3 Type qualifiers, says that the properties associated with qualified types are meaningful only for expressions that are lvalues.
>>
>> Seems to make the issue moot, since it says const-ness only applies to lvalues.
>>
>> So, I think both 6.3.15 and 6.5.3 imply that (char *) and (const char *) are compatible as the second and third operands in a conditional expression which is not an lvalue, which is the case in this code. As I mentioned above, gcc does not complain about this code. What do you think?
>>
>> Larry Baker
>> US Geological Survey
>> 650-329-5608
>> baker_at_[hidden]
>
> I could inquire about the current status of this TPR if you like. (Might as well.)
>
> Larry Baker
> US Geological Survey
> 650-329-5608
> baker_at_[hidden]
>
>
>
> On 17 Jan 2014, at 11:28 AM, Paul Hargrove wrote:
>
>> Ralph,
>>
>> You are probably right that the string literals are a likely cause (type char[] ? ).
>> I will poke at this a bit by adding (char *) casts to see which argument(s) are actually the cause and get back to you.
>>
>> -Paul
>>
>>
>> On Fri, Jan 17, 2014 at 8:56 AM, Ralph Castain <rhc_at_[hidden]> wrote:
>> Hi Paul
>>
>> Looking at these, I'm a tad puzzled. It would appear that PGI is complaining about the fixed string being passed in the last three cases as there is no (const char*)foo being used in those areas. Yet we use that same logic elsewhere and your report isn't showing those as warnings.
>>
>> Do you think it is the fixed string that is the issue - or is it the (const char*) variable we need to recast?
>>
>>
>> On Jan 16, 2014, at 11:24 PM, Paul Hargrove <phhargrove_at_[hidden]> wrote:
>>
>>> My builds of the trunk with pgcc-13.10 turned up the following warnings:
>>>
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 354)
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 376)
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 452)
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 534)
>>>
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/orte/mca/state/base/state_base_fns.c: 766)
>>>
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/orte/mca/plm/rsh/plm_rsh_component.c: 368)
>>>
>>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/orte/mca/plm/rsh/plm_rsh_module.c: 1337)
>>>
>>> I believe all of these are related to passing a (const char *) to OPAL_OUTPUT_VERBOSE().
>>>
>>> -Paul
>>>
>>>
>>> --
>>> Paul H. Hargrove PHHargrove_at_[hidden]
>>> Future Technologies Group
>>> Computer and Data Sciences Department Tel: +1-510-495-2352
>>> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
>>> _______________________________________________
>>> devel mailing list
>>> devel_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>
>>
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>
>>
>>
>> --
>> Paul H. Hargrove PHHargrove_at_[hidden]
>> Future Technologies Group
>> Computer and Data Sciences Department Tel: +1-510-495-2352
>> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>
>
>
>
> --
> Paul H. Hargrove PHHargrove_at_[hidden]
> Future Technologies Group
> Computer and Data Sciences Department Tel: +1-510-495-2352
> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900