ARM: 9480/1: entry: expand comment in __switch_tografted

As per discussion between the developers in the mail thread
linked, expand the comment in __switch_to so that readers
of the code understand what is going on.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 26 insertions, 0 deletions

diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
new file mode 100644
index 000000000..19f693b68
--- /dev/null
+++ b/scripts/Makefile.kcsan
@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: GPL-2.0
+# GCC and Clang accept backend options differently. Do not wrap in cc-option,
+# because Clang accepts "--param" even if it is unused.
+ifdef CONFIG_CC_IS_CLANG
+cc-param = -mllvm -$(1)
+else
+cc-param = --param $(1)
+endif
+
+# Keep most options here optional, to allow enabling more compilers if absence
+# of some options does not break KCSAN nor causes false positive reports.
+kcsan-cflags := -fsanitize=thread -fno-optimize-sibling-calls \
+	$(call cc-option,$(call cc-param,tsan-compound-read-before-write=1),$(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1))) \
+	$(call cc-param,tsan-distinguish-volatile=1)
+
+ifdef CONFIG_CC_IS_GCC
+# GCC started warning about operations unsupported by the TSan runtime. But
+# KCSAN != TSan, so just ignore these warnings.
+kcsan-cflags += -Wno-tsan
+endif
+
+ifndef CONFIG_KCSAN_WEAK_MEMORY
+kcsan-cflags += $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0))
+endif
+
+export CFLAGS_KCSAN := $(kcsan-cflags)