[cfe-dev] How to add a new calling convention?
David Chisnall via cfe-dev
cfe-dev at lists.llvm.org
Wed Jul 14 04:52:56 PDT 2021
On 13/07/2021 07:47, Gaier, Bjoern via cfe-dev wrote:
> Thank you for the reply guys :D
> Seems like adding the calling convention might bring more pain then I thought...
> Is it a better idea to tackle this issue on IR level then? Making Clang to not compile to object files, but IR instead, patching the effected calls and then passing it to static compiler? I haven't done such a thing so I honestly have no idea how easy it is to locate the calls that need patching (not every function call would need that) and then actually applying the patch.
I think you need to do both parts anyway: clang doesn't generate object
code, clang generates LLVM IR and LLVM generates object code. If you
want a new calling convention exposed to C/C++ then you first need to
expose a new clang calling convention, make clang lower it to a new IR
calling convention, and then modify the back ends to handle the new
The good news is that if you add the calling conventions to the two
enums (for C in clang, for IR in LLVM) and run a build with something
like `ninja -k100` then it will tell you all of the places outside of
the back end where you need to add handling for your new calling
convention. You can probably find a similar example near all of these
to copy. I've done this a bunch of times and never felt the need to
note down all of the places because the incomplete enum coverage in
switch warning finds them all for me.
You need to modify a *lot* of places, but each individual change is
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