[PATCH] make: Add a command line option for debugging OpenSBI

[Bin Meng]

Add a new make command line option "make DEBUG=1" to prevent compiler
optimizations using -O2.

Signed-off-by: Bin Meng <bmeng at tinylab.org>
---

 Makefile  |  7 ++++++-
 README.md | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index b20404f..a26a39b 100644
--- a/Makefile
+++ b/Makefile
@@ -331,7 +331,12 @@ GENFLAGS	+=	$(libsbiutils-genflags-y)
 GENFLAGS	+=	$(platform-genflags-y)
 GENFLAGS	+=	$(firmware-genflags-y)
 
-CFLAGS		=	-g -Wall -Werror -ffreestanding -nostdlib -fno-stack-protector -fno-strict-aliasing -O2
+CFLAGS		=	-g -Wall -Werror -ffreestanding -nostdlib -fno-stack-protector -fno-strict-aliasing
+ifneq ($(DEBUG),)
+CFLAGS		+=	-O0
+else
+CFLAGS		+=	-O2
+endif
 CFLAGS		+=	-fno-omit-frame-pointer -fno-optimize-sibling-calls -mstrict-align
 # enable -m(no-)save-restore option by CC_SUPPORT_SAVE_RESTORE
 ifeq ($(CC_SUPPORT_SAVE_RESTORE),y)
diff --git a/README.md b/README.md
index 895bbf2..a6bcb0c 100644
--- a/README.md
+++ b/README.md
@@ -298,6 +298,19 @@ NOTE: Using `BUILD_INFO=y` without specifying SOURCE_DATE_EPOCH will violate
 purpose, and should NOT be used in a product which follows "reproducible
 builds".
 
+Building with optimization off for debugging
+--------------------------------------------
+
+When debugging OpenSBI, we may want to turn off the compiler optimization and
+make debugging produce the expected results for a better debugging experience.
+To build with optimization off we can just simply add `DEBUG=1`, like:
+```
+make DEBUG=1
+```
+
+This definition is ONLY for development and debug purpose, and should NOT be
+used in a product build.
+
 Contributing to OpenSBI
 -----------------------
 
-- 
2.25.1