llvm dev - Sep 2009 - [LLVMdev] llc and debug information

Hi all,

I'm having an issue with debug information and llc.  A test program:

#include <iostream>

using namespace std;

void foo() {
    cout << "My return address is " <<
__builtin_return_address(0) <<
        endl << flush;
}

int main(int argc, char *argv[]) {
    foo();
    return 0;
}


When I compile my test program to LLVM bytecode, and then use llc to take
the bytecode to assembly, llc appears to strip the debugging information
along the way:
> llvm-g++ -g -c -emit-llvm test.cpp
> llc test.o
> g++ test.o.s
> ./a.out
My return address is 0x400b92
> addr2line 0x400b92
??:0

My goal is to run a transformation pass on the bytecode to put in a few
instrumentation hooks for a dynamic analysis I'm writing.  Debug
information, even if it's a little off, would be extremely useful to have in
the final binary.  This build chain worked with a 2.6svn version of llc
(that is, the final binary would have debug information which corresponded
reasonably well to the source.  Also it seemed to work when this question
was sent http://lists.cs.uiuc.edu/pipermail/llvmdev/2009-April/021697.html),
but I recently upgraded to a 2.7svn version with the results above.  Is this
change intended?  Is there a way tell llc to keep debug information in?

Thanks!
Nick
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2009/9/16 Nick Jalbert <jalbert at
eecs.berkeley.edu>:
>> llvm-g++ -g -c -emit-llvm test.cpp
I always use -O0 together with -g because I had far too many problems
of the like already to define on the fly if it's safe or not *not* to
use it.

Maybe that helps...

cheers,
--renato

Reclaim your digital rights, eliminate DRM, learn more at
http://www.defectivebydesign.org/what_is_drm

On Wed, Sep 16, 2009 at 1:34 PM, Nick Jalbert <jalbert at
eecs.berkeley.edu> wrote:
> Hi all,
> I'm having an issue with debug information and llc.  A test program:
> #include <iostream>
> using namespace std;
> void foo() {
>     cout << "My return address is " <<
__builtin_return_address(0) <<
>         endl << flush;
> }
> int main(int argc, char *argv[]) {
>     foo();
>     return 0;
> }
>
> When I compile my test program to LLVM bytecode, and then use llc to take
> the bytecode to assembly, llc appears to strip the debugging information
> along the way:
>> llvm-g++ -g -c -emit-llvm test.cpp
>> llc test.o
try -O0 in llc command line.
-
Devang

Thanks for the quick responses, but unfortunately still no
luck:
> llvm-g++ -g -O0 -c -emit-llvm test.cpp
> llc -O0 test.o
> g++ test.o.s
> ./a.out
My return address is 0x400bb2
> addr2line 0x400bb2
??:0

Also to further implicate llc, this works:
> llvm-g++ -g -O0 -S test.cpp
> g++ test.s
> ./a.out
My return address is 0x400bf9
> addr2line 0x400bf9
/home/jalbert/llvmtest//test.cpp:13

Anymore thoughts?

-Nick


On Wed, Sep 16, 2009 at 2:29 PM, Devang Patel <devang.patel at
gmail.com>wrote:
> On Wed, Sep 16, 2009 at 1:34 PM, Nick Jalbert <jalbert at
eecs.berkeley.edu>
> wrote:
> > Hi all,
> > I'm having an issue with debug information and llc.  A test
program:
> > #include <iostream>
> > using namespace std;
> > void foo() {
> >     cout << "My return address is " <<
__builtin_return_address(0) <<
> >         endl << flush;
> > }
> > int main(int argc, char *argv[]) {
> >     foo();
> >     return 0;
> > }
> >
> > When I compile my test program to LLVM bytecode, and then use llc to
take
> > the bytecode to assembly, llc appears to strip the debugging
information
> > along the way:
> >> llvm-g++ -g -c -emit-llvm test.cpp
> >> llc test.o
>
> try -O0 in llc command line.
> -
> Devang
>
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