Svadev mailing list

[Krzysztof Cieniuch <cieniuch77 AT gmail.com>]

On 07/20/13 23:51, John Criswell wrote:
> On 7/18/13 11:35 AM, Krzysztof Cieniuch wrote:
> > Hi,
> >
> > I'm using CentOS 6.3, clang version 3.2  with latest ld checked out 
> > from cvs
> > I followed instructions on wiki and installed clang with lto (gold 
> > plugin)
>
> Are you using libstdc++ that is installed on your system, or did you 
> build compiler_rt?  I've never used compiler_rt with SAFECode.

I'm using libstdc++

> > I'm having troubles compiling this simple program:
> >
> > #include<string>
> > #include<map>
> > #include<iostream>
> >
> > using namespace std;
> > int main(int argc,char** argv){
> >     map<string,int> themap;
> >     string test(argv[0]);
> >
> >     themap["key1"]=1;
> >     cout << test << endl;
> >
> >     return 0;
> > }
> >
> > clang++ -g  -O2 -flto -use-gold-plugin -fmemsafety  -o main main.cc  
> > -L /opt/SAFECode/lib
> >
> > FIXME: Ignoring global of size zero: 
> > @_ZNSs4_Rep20_S_empty_rep_storageE = external global [0 x i64]
> > lto-llvm.o-O8q9Q2:ld-temp.o:TargetList: error: undefined reference to 
> > 'std::string::_S_compare(unsigned long, unsigned long)'
> > lto-llvm.o-O8q9Q2:ld-temp.o:TargetList1: error: undefined reference 
> > to 'std::string::_S_compare(unsigned long, unsigned long)'
> >
> > If I remove -O2 option it links fine.
> > What's strange if you comment  out line:  themap["key1"]=1; it will 
> > compile.
> > What even more strange :-) if you comment out:  cout << test << endl; 
> > instead it will also compile any ideas ?
>
> As to why the problem goes away because of some of these changes, I 
> think the issue is that:
>
> 1) Removing themap["key1"]=1 removes the string comparison, so the 
> string comparison method is no longer needed.
>
> 2) Removing the cout line means that your program is identical to a 
> program that just exits with status 0.  LLVM is optimizing all the 
> other code out, so again, the undefined symbol no longer appears in 
> the program.
Thanks for great  explanation

> > Is this bug in clang ld or libstdc++ on centos 6.3 or combination of 
> > all.
>
> I took a quick look, and it's a bug in SAFECode's CFI transform. The 
> reason why this is happening is because SAFECode creates a global 
> variable with a list of function targets.  Included in this list are 
> functions with available_externally linkage.  Such functions never get 
> emitted into the executable even though they appear in the IR.  I 
> think the correct fix is for the CFI pass to not consider such 
> functions as valid targets of indirect function calls.
>
> Can you file a bug report with the above information?  I can probably 
> get a fix working by late next week (I'm busy until Wednesday on a 
> paper).  In the meantime, try working around the problem by not using 
> -O2.
>
> -- John T.

No problem I've got lots of other issue sto fix with clang copitaion 
this will keep me busy for some time. Ticked created: Bug 16672

BTW Do you have any information about using SAFECode with large scale 
projects how it compares to Valgrind performance wise.
Is it possible to ignore some errors  i.e. any mechanism to valgrind 
suppressions ?

Thanks
Krzysztof