path: root/scripts/asn1_compiler.c
diff options
authorDavid Howells <>2015-08-05 12:54:46 +0100
committerDavid Howells <>2015-08-05 12:54:46 +0100
commit3f3af97d8225a58ecdcde7217c030b17e5198226 (patch)
tree2d229cf5aa9309eb3ab74018c438da93d3942ab0 /scripts/asn1_compiler.c
parent8d9b21dcfe6814c92c9f445a7c742b7bab4f86b8 (diff)
ASN.1: Fix actions on CHOICE elements with IMPLICIT tags
In an ASN.1 description where there is a CHOICE construct that contains elements with IMPLICIT tags that refer to constructed types, actions to be taken on those elements should be conditional on the corresponding element actually being matched. Currently, however, such actions are performed unconditionally in the middle of processing the CHOICE. For example, look at elements 'b' and 'e' here: A ::= SEQUENCE { CHOICE { b [0] IMPLICIT B ({ do_XXXXXXXXXXXX_b }), c [1] EXPLICIT C ({ do_XXXXXXXXXXXX_c }), d [2] EXPLICIT B ({ do_XXXXXXXXXXXX_d }), e [3] IMPLICIT C ({ do_XXXXXXXXXXXX_e }), f [4] IMPLICIT INTEGER ({ do_XXXXXXXXXXXX_f }) } } ({ do_XXXXXXXXXXXX_A }) B ::= SET OF OBJECT IDENTIFIER ({ do_XXXXXXXXXXXX_oid }) C ::= SET OF INTEGER ({ do_XXXXXXXXXXXX_int }) They each have an action (do_XXXXXXXXXXXX_b and do_XXXXXXXXXXXX_e) that should only be processed if that element is matched. The problem is that there's no easy place to hang the action off in the subclause (type B for element 'b' and type C for element 'e') because subclause opcode sequences can be shared. To fix this, introduce a conditional action opcode(ASN1_OP_MAYBE_ACT) that the decoder only processes if the preceding match was successful. This can be seen in an excerpt from the output of the fixed ASN.1 compiler for the above ASN.1 description: [ 13] = ASN1_OP_COND_MATCH_JUMP_OR_SKIP, // e [ 14] = _tagn(CONT, CONS, 3), [ 15] = _jump_target(45), // --> C [ 16] = ASN1_OP_MAYBE_ACT, [ 17] = _action(ACT_do_XXXXXXXXXXXX_e), In this, if the op at [13] is matched (ie. element 'e' above) then the action at [16] will be performed. However, if the op at [13] doesn't match or is skipped because it is conditional and some previous op matched, then the action at [16] will be ignored. Note that to make this work in the decoder, the ASN1_OP_RETURN op must set the flag to indicate that a match happened. This is necessary because the _jump_target() seen above introduces a subclause (in this case an object of type 'C') which is likely to alter the flag. Setting the flag here is okay because to process a subclause, a match must have happened and caused a jump. This cannot be tested with the code as it stands, but rather affects future code. Signed-off-by: David Howells <> Reviewed-by: David Woodhouse <>
Diffstat (limited to 'scripts/asn1_compiler.c')
1 files changed, 2 insertions, 1 deletions
diff --git a/scripts/asn1_compiler.c b/scripts/asn1_compiler.c
index e87359cd23c0..0515bced929a 100644
--- a/scripts/asn1_compiler.c
+++ b/scripts/asn1_compiler.c
@@ -1468,7 +1468,8 @@ dont_render_tag:
case TYPE_REF:
render_element(out, e->type->type->element, tag);
if (e->action)
- render_opcode(out, "ASN1_OP_ACT,\n");
+ render_opcode(out, "ASN1_OP_%sACT,\n",
+ skippable ? "MAYBE_" : "");