[Skiboot] [RFC 5/8] secvar: add build-time mechanism to inject default variable data

[Eric Richter]

To allow the implementation of a backend that uses static, built-in
variables, this patch adds the ability to compile in a blob of data,
accessible by symbol named similarly to the file in which the data was
loaded from.

To operate: place a file in the libstb/secvar/defaultvars directory named
`secvar_default_NAME.var`, where NAME is the case-sensitive name of the
variable the static-variable enabled backend will expect it to be.

For example, to build in a db into the forthcoming edk2-compat-static
driver, copy the db.esl file into the aforementioned directory as
`secvar_default_db.var`. This will be compiled in, and exposed in the
secvar_default_vars.h header, which will look something like:

uint8_t secvar_default_db[] = { ... };
\#define SECVAR_DEFAULT_DB

The #define may be used by backends to determine if a default variable was
provided for a specific variable it may expect.

RFC NOTE: This is a rather janky first implementation, and ideally should
be improved in some form. I am open to suggestions on how to improve this.
Ideally at minimum, the backend should be able to "discover" which
variables have been built in.

Furthermore, there should likely be some kind of trigger to detect whether
or not default keys have been built in at all, but that is something that
will come up in a later patch.

Signed-off-by: Eric Richter <erichte at linux.ibm.com>
---
 Makefile.main                          |  1 +
 libstb/secvar/Makefile.inc             |  3 ++-
 libstb/secvar/defaultvars/Makefile.inc | 31 ++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 libstb/secvar/defaultvars/Makefile.inc

diff --git a/Makefile.main b/Makefile.main
index c8a63e8b..d0b5d4eb 100644
--- a/Makefile.main
+++ b/Makefile.main
@@ -409,6 +409,7 @@ clean:
 	$(RM) include/asm-offsets.h version.c .version
 	$(RM) skiboot.info external/gard/gard.info external/pflash/pflash.info
 	$(RM) extract-gcov $(TARGET).lid.stb $(TARGET).lid.xz.stb
+	$(RM) libstb/secvar/defaultvars/*.{c,d,o,h}
 
 distclean: clean
 	$(RM) *~ $(SUBDIRS:%=%/*~) include/*~
diff --git a/libstb/secvar/Makefile.inc b/libstb/secvar/Makefile.inc
index 57c7cfb5..1d6f4c81 100644
--- a/libstb/secvar/Makefile.inc
+++ b/libstb/secvar/Makefile.inc
@@ -8,5 +8,6 @@ SECVAR = libstb/secvar/built-in.a
 
 include $(SRC)/libstb/secvar/storage/Makefile.inc
 include $(SRC)/libstb/secvar/backend/Makefile.inc
+include $(SRC)/libstb/secvar/defaultvars/Makefile.inc
 
-$(SECVAR): $(SECVAR_OBJS:%=libstb/secvar/%) $(SECVAR_STORAGE) $(SECVAR_BACKEND)
+$(SECVAR): $(SECVAR_OBJS:%=libstb/secvar/%) $(SECVAR_DEFAULTVARS) $(SECVAR_STORAGE) $(SECVAR_BACKEND)
diff --git a/libstb/secvar/defaultvars/Makefile.inc b/libstb/secvar/defaultvars/Makefile.inc
new file mode 100644
index 00000000..f831413d
--- /dev/null
+++ b/libstb/secvar/defaultvars/Makefile.inc
@@ -0,0 +1,31 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+# -*-Makefile-*-
+
+SECVAR_DEFAULTVARS_DIR = libstb/secvar/defaultvars
+
+SUBDIRS += $(SECVAR_DEFAULTVARS_DIR)
+
+SECVAR_DEFAULTVARS_FILES = $(wildcard $(SECVAR_DEFAULTVARS_DIR)/secvar_default_*.var)
+SECVAR_DEFAULTVARS_C_FILES = $(patsubst %.var,%.c,$(notdir $(SECVAR_DEFAULTVARS_FILES)))
+SECVAR_DEFAULTVARS_OBJS = $(patsubst %.c,%.o,$(SECVAR_DEFAULTVARS_C_FILES))
+
+$(SECVAR_DEFAULTVARS_DIR)/secvar_default_vars.h: $(SECVAR_DEFAULTVARS_FILES)
+	echo -n "" > $@
+	for var in $(subst .var,,$(notdir $^)) ; do \
+		echo "#ifndef _SECVAR_DEFAULTVARS_H_" >> $@ ; \
+		echo "#define _SECVAR_DEFAULTVARS_H_" >> $@ ; \
+		echo "extern unsigned char *$$var;" >> $@ ; \
+		echo -n "#define " >> $@ ; \
+		echo $$var | tr [:lower:] [:upper:] >> $@ ; \
+		echo "#endif" >> $@ ; \
+	done;
+
+secvar_default_%.c: secvar_default_%.var $(SECVAR_DEFAULTVARS_DIR)/secvar_default_vars.h
+	echo $^
+	echo "unsigned char $(subst .var,,$(notdir $<))[] = {" > $@
+	cat $^ | xxd -e -i >> $@
+	echo "};" >> $@
+
+SECVAR_DEFAULTVARS = $(SECVAR_DEFAULTVARS_DIR)/built-in.a
+
+$(SECVAR_DEFAULTVARS): $(SECVAR_DEFAULTVARS_OBJS:%=$(SECVAR_DEFAULTVARS_DIR)/%)
-- 
2.33.0