[PATCH v4 0/2] Support kexec/kdump for clang built kernel

[Nick Desaulniers]

1. Reuse the implementation of memcpy and memset instead of relying on
__builtin_memcpy and __builtin_memset as it causes infinite recursion
in Clang (at any opt level) or GCC at -O2.
2. Don't reset KBUILD_CFLAGS, rather filter CONFIG_FUNCTION_TRACER,
CONFIG_STACKPROTECTOR, and CONFIG_STACKPROTECTOR_STRONG flags via
`CFLAGS_REMOVE_<file>.o'

A good test of this series (besides boot testing a kexec kernel):
* There should be no undefined symbols in arch/x86/purgatory/purgatory.ro:
$ nm arch/x86/purgatory/purgatory.ro
  particularly `warn`, `bcmp`, `__stack_chk_fail`, `memcpy` or `memset`.
* `-pg`, `-fstack-protector`, `-fstack-protector-strong` should not be
  added to the command line for the c source files under arch/x86/purgatory/
  when compiling with CONFIG_FUNCTION_TRACER=y, CONFIG_STACKPROTECTOR=y,
  and CONFIG_STACKPROTECTOR_STRONG=y.

V4 of: https://lkml.org/lkml/2019/7/23/864

Nick Desaulniers (2):
  x86/purgatory: do not use __builtin_memcpy and __builtin_memset
  x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS

 arch/x86/boot/string.c         |  7 +++++++
 arch/x86/purgatory/Makefile    | 29 ++++++++++++++++++++++++-----
 arch/x86/purgatory/purgatory.c |  6 ++++++
 arch/x86/purgatory/string.c    | 23 -----------------------
 4 files changed, 37 insertions(+), 28 deletions(-)
 delete mode 100644 arch/x86/purgatory/string.c

-- 
2.22.0.709.g102302147b-goog