X.509: Add simple ASN.1 grammar compiler

Add a simple ASN.1 grammar compiler.  This produces a bytecode output that can
be fed to a decoder to inform the decoder how to interpret the ASN.1 stream it
is trying to parse.

Action functions can be specified in the grammar by interpolating:

	({ foo })

after a type, for example:

	SubjectPublicKeyInfo ::= SEQUENCE {
		algorithm		AlgorithmIdentifier,
		subjectPublicKey	BIT STRING ({ do_key_data })
		}

The decoder is expected to call these after matching this type and parsing the
contents if it is a constructed type.

The grammar compiler does not currently support the SET type (though it does
support SET OF) as I can't see a good way of tracking which members have been
encountered yet without using up extra stack space.

Currently, the grammar compiler will fail if more than 256 bytes of bytecode
would be produced or more than 256 actions have been specified as it uses
8-bit jump values and action indices to keep space usage down.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

scripts/.gitignore

@@ -10,3 +10,4 @@ ihex2fw
 recordmcount
 docproc
 sortextable
+asn1_compiler

scripts/Makefile

@@ -16,8 +16,10 @@ hostprogs-$(CONFIG_VT)           += conmakehash
 hostprogs-$(CONFIG_IKCONFIG)     += bin2c
 hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
 hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
+hostprogs-$(CONFIG_ASN1)	 += asn1_compiler
 
 HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
+HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
 
 always		:= $(hostprogs-y) $(hostprogs-m)
 

scripts/Makefile.build

@@ -354,6 +354,17 @@ quiet_cmd_cpp_lds_S = LDS     $@
 $(obj)/%.lds: $(src)/%.lds.S FORCE
 	$(call if_changed_dep,cpp_lds_S)
 
+# ASN.1 grammar
+# ---------------------------------------------------------------------------
+quiet_cmd_asn1_compiler = ASN.1   $@
+      cmd_asn1_compiler = $(objtree)/scripts/asn1_compiler $< \
+				$(subst .h,.c,$@) $(subst .c,.h,$@)
+
+.PRECIOUS: $(objtree)/$(obj)/%-asn1.c $(objtree)/$(obj)/%-asn1.h
+
+$(obj)/%-asn1.c $(obj)/%-asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler
+	$(call cmd,asn1_compiler)
+
 # Build the compiled-in targets
 # ---------------------------------------------------------------------------