[llvm] r196158 - Debug Info: drop debug info via upgrading path if version number does not match.

[Manman Ren]

On Mon, Dec 2, 2013 at 4:26 PM, Eric Christopher <echristo at gmail.com> wrote:

> On Mon, Dec 2, 2013 at 4:21 PM, Manman Ren <manman.ren at gmail.com> wrote:
> >
> >
> >
> > On Mon, Dec 2, 2013 at 2:07 PM, Eric Christopher <echristo at gmail.com>
> wrote:
> >>
> >> > Add a helper function getDebugInfoVersionFromModule to return the
> debug
> >> > info
> >> > version number for a module.
> >> >
> >>
> >> I think this should be getDebugMetadataVersionFromModule since this
> >> could be easily confused with the dwarf version that someone has asked
> >> for.
> >
> >
> > Done in r196172.
> >>
> >>
> >> > "Verifier/module-flags-1.ll" checks for verification errors.
> >> > It will seg fault when calling getDebugInfoVersionFromModule because
> of
> >> > the
> >> > incorrect format for module flags in the testing case. We make
> >> > getModuleFlagsMetadata more robust by checking for error conditions.
> >> >
> >>
> >> I'm not sure what's going on here, can you elaborate?
> >
> >
> > We have the code path and the verification path. Code path should not seg
> > fault when the format of a module flag is incorrect (as in the testing
> case
> > Verifier/module-flags-1.ll).
> > module-flags-1.ll tries to make sure that the verifier dumps the right
> error
> > message when the format of a module flag is incorrect.
> >
> > Before this patch, the code path will seg fault because we don't perform
> > error checking in the code path as shown below.
> >
>
> You seem to be hard coding certain operations leading me to believe
> there's some specific format here that you're looking for, but it's
> not obvious what it is


Can you be specific on where I am hard coding operations?


> - are you saying that if you turn off the
> verifier we'll crash on certain types of bitcode files that normally
> we wouldn't be able to read anyhow since we'd fail verification?
>

No, it does not matter whether the verifier is on or off. The code path
should not seg fault when the input bit code has incorrect module flag.

The reason my patch exposes the seg fault is that we parse the module flag
before
the verifier and the testing case will seg fault before getting the
verification error.

Manman


>
> -eric
>
> > Cheers,
> > Manman
> >
> >>
> >>
> >> > Modified: llvm/trunk/lib/IR/Module.cpp
> >> > URL:
> >> >
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Module.cpp?rev=196158&r1=196157&r2=196158&view=diff
> >> >
> >> >
> ==============================================================================
> >> > --- llvm/trunk/lib/IR/Module.cpp (original)
> >> > +++ llvm/trunk/lib/IR/Module.cpp Mon Dec  2 15:29:56 2013
> >> > @@ -318,11 +318,16 @@ getModuleFlagsMetadata(SmallVectorImpl<M
> >> >
> >> >    for (unsigned i = 0, e = ModFlags->getNumOperands(); i != e; ++i) {
> >> >      MDNode *Flag = ModFlags->getOperand(i);
> >> > -    ConstantInt *Behavior = cast<ConstantInt>(Flag->getOperand(0));
> >> > -    MDString *Key = cast<MDString>(Flag->getOperand(1));
> >> > -    Value *Val = Flag->getOperand(2);
> >> > -
> >> >
> Flags.push_back(ModuleFlagEntry(ModFlagBehavior(Behavior->getZExtValue()),
> >> > -                                    Key, Val));
> >> > +    if (Flag->getNumOperands() >= 3 &&
> >> > isa<ConstantInt>(Flag->getOperand(0)) &&
> >> > +        isa<MDString>(Flag->getOperand(1))) {
> >> > +      // Check the operands of the MDNode before accessing the
> >> > operands.
> >> > +      // The verifier will actually catch these failures.
> >> > +      ConstantInt *Behavior = cast<ConstantInt>(Flag->getOperand(0));
> >> > +      MDString *Key = cast<MDString>(Flag->getOperand(1));
> >> > +      Value *Val = Flag->getOperand(2);
> >> > +
> >> >
> Flags.push_back(ModuleFlagEntry(ModFlagBehavior(Behavior->getZExtValue()),
> >> > +                                      Key, Val));
> >> > +    }
> >> >    }
> >> >  }
> >> >
> >> >
> >> > _______________________________________________
> >> > llvm-commits mailing list
> >> > llvm-commits at cs.uiuc.edu
> >> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >
> >
>
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