When the code is built with -mbackchain, it is possible to retrieve the
caller's frame and return addresses. GCC already can do this, add this
support to Clang as well. Use RISCVTargetLowering and GCC's
s390_return_addr_rtx() as inspiration. Add tests based on what GCC is
emitting.
The LIT test cases were migrated with the script provided by
Nikita Popov.
No manual changes were made. Committed without review since
no functional changes, after consultation with uweigand.
In order to use __builtin_frame_address(0) with packed stack and no
backchain, the address of where the backchain would have been written is
returned (like GCC).
This address may either contain a saved register or be unused.
Review: Ulrich Weigand
Differential Revision: https://reviews.llvm.org/D101897
In order to build the Linux kernel, the back chain must be supported with
packed-stack. The back chain is then stored topmost in the register save
area.
Review: Ulrich Weigand
Differential Revision: https://reviews.llvm.org/D74506
