GCC has plans  to add a new switch that enables finer-grained control
of the insertion of CET stuff in generated code. This patch duplicates
their implementation within LLVM, in the hope that it can also be used
by Xen maintainers.
- 8< --
With -fcf-protection=branch, clang automatically adds control-flow
protection to indirect calls and jumps. On X86, this translates to ENDBR
instructions being added to the prologues of functions.
This patch adds a new switch, '-mmanual-endbr', which tells the compiler
that, even though -fcf-protection is in use, functions should not get
the instrumentation automatically. Instead, it allows users to manually
add the new attribute, 'cf_check', to functions that require it.
Depends on D118052.