[PATCH] Makefile: Add build time and compiler info string.

[wefu at redhat.com]

From: Wei Fu <wefu at redhat.com>

When we are doing opensbi development, we want to know the build time
and compiler info for debug purpose.
To enable this message, please add "BUILD_INFO=y" , like:

```
make BUILD_INFO=y
```

NOTE: `BUILD_INFO=y` will violate "reproducible builds".
So it's ONLY for development and debug purpose, and should NEVER be used
in a real product.

Signed-off-by: Wei Fu <wefu at redhat.com>
---
 Makefile           | 21 ++++++++++++++++++++-
 README.md          | 16 ++++++++++++++++
 lib/sbi/sbi_init.c |  4 ++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 16d9dca..c678a1e 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@
 # Authors:
 #   Anup Patel <anup.patel at wdc.com>
 #
-
+BUILD_INFO ?= n
 # Select Make Options:
 # o  Do not use make's built-in rules
 # o  Do not print "Entering directory ...";
@@ -150,6 +150,11 @@ endif
 # Check whether the linker supports creating PIEs
 OPENSBI_LD_PIE := $(shell $(CC) $(CLANG_TARGET) $(RELAX_FLAG) $(USE_LD_FLAG) -fPIE -nostdlib -Wl,-pie -x c /dev/null -o /dev/null >/dev/null 2>&1 && echo y || echo n)
 
+ifeq ($(BUILD_INFO),y)
+OPENSBI_BUILD_TS=$(shell date)
+OPENSBI_COMPILER_VERSION_TEXT=$(shell $(CC) -v 2>&1 | grep ' version ' | sed 's/[[:space:]]*$$//')
+endif
+
 # Setup list of objects.mk files
 ifdef PLATFORM
 platform-object-mks=$(shell if [ -d $(platform_src_dir)/ ]; then find $(platform_src_dir) -iname "objects.mk" | sort -r; fi)
@@ -247,6 +252,11 @@ GENFLAGS	+=	-I$(include_dir)
 ifneq ($(OPENSBI_VERSION_GIT),)
 GENFLAGS	+=	-DOPENSBI_VERSION_GIT="\"$(OPENSBI_VERSION_GIT)\""
 endif
+ifeq ($(BUILD_INFO),y)
+GENFLAGS	+=	-DBUILD_INFO
+GENFLAGS	+=	-DOPENSBI_BUILD_TS="\"$(OPENSBI_BUILD_TS)\""
+GENFLAGS	+=	-DOPENSBI_COMPILER_VERSION_TEXT="\"$(OPENSBI_COMPILER_VERSION_TEXT)\""
+endif
 GENFLAGS	+=	$(libsbiutils-genflags-y)
 GENFLAGS	+=	$(platform-genflags-y)
 GENFLAGS	+=	$(firmware-genflags-y)
@@ -398,6 +408,12 @@ $(build_dir)/%.dep: $(src_dir)/%.c
 $(build_dir)/%.o: $(src_dir)/%.c
 	$(call compile_cc,$@,$<)
 
+ifeq ($(BUILD_INFO),y)
+$(build_dir)/lib/sbi/sbi_init.o: $(libsbi_dir)/sbi_init.c FORCE
+	$(call compile_cc,$@,$<)
+	$(warning 'BUILD_INFO=y' violates 'reproducible builds', for DEBUG ONLY.)
+endif
+
 $(build_dir)/%.dep: $(src_dir)/%.S
 	$(call compile_as_dep,$@,$<)
 
@@ -551,3 +567,6 @@ ifeq ($(install_root_dir),$(install_root_dir_default)/usr)
 	$(if $(V), @echo " RM        $(install_root_dir_default)")
 	$(CMD_PREFIX)rm -rf $(install_root_dir_default)
 endif
+
+.PHONY: FORCE
+FORCE:
diff --git a/README.md b/README.md
index 9fdf097..68a4902 100644
--- a/README.md
+++ b/README.md
@@ -254,6 +254,21 @@ to produce broken binaries with missing relocations; it is therefore currently
 recommended that this combination be avoided or *FW_PIC=n* be used to disable
 building OpenSBI as a position-independent binary.
 
+Building with timestamp and compiler info
+------------------------
+
+When doing development, we may want to know the build time and compiler info
+for debug purpose. OpenSBI can also be built with timestamp and compiler info.
+To build with those info and print it out at boot time, we can just simply add
+`BUILD_INFO=y`, like:
+```
+make BUILD_INFO=y
+```
+
+NOTE: Using `BUILD_INFO=y` will violate [reproducible builds]. This definition
+is ONLY for development and debug purpose. It should NEVER be used in a real
+product.
+
 Contributing to OpenSBI
 -----------------------
 
@@ -336,3 +351,4 @@ make I=<install_directory> install_docs
 [Doxygen manual]: http://www.doxygen.nl/manual/index.html
 [Kendryte standalone SDK]: https://github.com/kendryte/kendryte-standalone-sdk
 [third party notices]: ThirdPartyNotices.md
+[reproducible builds]: https://reproducible-builds.org
\ No newline at end of file
diff --git a/lib/sbi/sbi_init.c b/lib/sbi/sbi_init.c
index 6ef8742..7311c13 100644
--- a/lib/sbi/sbi_init.c
+++ b/lib/sbi/sbi_init.c
@@ -48,6 +48,10 @@ static void sbi_boot_print_banner(struct sbi_scratch *scratch)
 		   OPENSBI_VERSION_MINOR);
 #endif
 
+#ifdef BUILD_INFO
+	sbi_printf("Build time: %s.\n", OPENSBI_BUILD_TS);
+	sbi_printf("Compiler: %s.\n", OPENSBI_COMPILER_VERSION_TEXT);
+#endif
 	sbi_printf(BANNER);
 }
 
-- 
2.25.4