How to link against specific targets? (Porting ShadowCallStack to new PM)

Hi all,

I'm in the process of trying to port ShadowCallStack from the legacy
pass manager to the new one. I ran into an issue though where it seems
I cannot link against anything I added in ShadowCallStack.cpp when
trying to build c-index-test (via just running ninja check-all). I
think the reason for this is because nothing under lib/Target/X86/ is
a part of any library compiled with c-index-test (if I'm reading the
CMake correctly). I imagine this would also mean I wouldn't be able to
successfully build other binaries like clang.

What I want to know is if there is a proper way to link against code
under lib/Target/X86/ (as a part of some shared library or through
some other means) such that i could use it with the new pass manager.

These are some other thoughts I had attempting to find a possible solution:
- I could not find an instance of classes under lib/Target/X86/ (or
any other target for that matter) that are used or exposed by anything
outside of lib/Target/
- The only things that seem exposed under lib/Target/ are a few files
packed into libLLVMTarget.a and none of it is linked against source
files under llvm/Target/<TARGET>
- If ShadowCallStack is meant to be a pass that should eventually work
for any target, at some point it could be pulled out from the X86
directory and also be included in libLLVMTarget.a, but I'm not sure
how the CMake dependency hierarchy would support this.

Thanks,
Leonard

Isn’t ShadowCallStack a MachineFunctionPass? Machine IR doesn’t use the new PM yet.

I made a second MachineFunctionPass that can run on new PM and made it
similar to the MachineFunctionPass for legacy PM. It seemed that the
only required analysis used by it was MachineModuleInfo which I also
made a new PM analysis for by separating it into 2 classes: 1 that
holds the meta information specific to a module, and 1 that's the pass
which holds an instance to the first class. The new PM analysis holds
an instance of this first class also. I'm not sure though if there are
new PM equivalents for the addPreserved analyses that
MachineFunctionPass has under it's getAnalysisUsage.

I can't figure out though how to port ShadowCallStack specifically,
assuming I completed all the necessary work for enabling
MachineFunctionPass in new PM, but I imagine that I may have missed a
few things that I didn't account for. I can share what I have
currently if you would like to see.

- Leonard

I think Craig’s point was that moving machine passes to the new PM hasn’t even started. MachineFunctions, MachineModuleInfo, none of it is going to work.

But you also don’t need it to work. -fexperimental-new-pass-manager only enables the new PM for the IR pipeline. The machine passes and all of the code generator are handled independently.

Hmmm. I'm probably underestimating the work, but do you know what
would need to be done in order to support machine passes in the new
PM?

Do you also happen to have any resources on how I could learn more
about the IR pipeline and how the new and legacy PM fit into it, aside
from just reading over the code?

Thanks,
Leonard