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 <dhowells@redhat.com>
Reviewed-by: David Woodhouse <David.Woodhouse@intel.com>
Fix the handling of CHOICE types in the ASN.1 compiler to make SEQUENCE and
SET elements in a CHOICE be correctly rendered as skippable and conditional
as appropriate.
For example, in the following ASN.1:
Foo ::= SEQUENCE { w1 INTEGER, w2 Bar, w3 OBJECT IDENTIFIER }
Bar ::= CHOICE {
x1 Seq1,
x2 [0] IMPLICIT OCTET STRING,
x3 Seq2,
x4 SET OF INTEGER
}
Seq1 ::= SEQUENCE { y1 INTEGER, y2 INTEGER, y3 INTEGER }
Seq2 ::= SEQUENCE { z1 BOOLEAN, z2 BOOLEAN, z3 BOOLEAN }
the output in foo.c generated by:
./scripts/asn1_compiler foo.asn1 foo.c foo.h
included:
// Bar
// Seq1
[ 4] = ASN1_OP_MATCH,
[ 5] = _tag(UNIV, CONS, SEQ),
...
[ 13] = ASN1_OP_COND_MATCH_OR_SKIP, // x2
[ 14] = _tagn(CONT, PRIM, 0),
// Seq2
[ 15] = ASN1_OP_MATCH,
[ 16] = _tag(UNIV, CONS, SEQ),
...
[ 24] = ASN1_OP_COND_MATCH_JUMP_OR_SKIP, // x4
[ 25] = _tag(UNIV, CONS, SET),
...
[ 27] = ASN1_OP_COND_FAIL,
as a result of the CHOICE - but this is wrong on lines 4 and 15 because
both of these should be skippable (one and only one of the four can be
picked) and the one on line 15 should also be conditional so that it is
ignored if anything before it matches.
After the patch, it looks like:
// Bar
// Seq1
[ 4] = ASN1_OP_MATCH_JUMP_OR_SKIP, // x1
[ 5] = _tag(UNIV, CONS, SEQ),
...
[ 7] = ASN1_OP_COND_MATCH_OR_SKIP, // x2
[ 8] = _tagn(CONT, PRIM, 0),
// Seq2
[ 9] = ASN1_OP_COND_MATCH_JUMP_OR_SKIP, // x3
[ 10] = _tag(UNIV, CONS, SEQ),
...
[ 12] = ASN1_OP_COND_MATCH_JUMP_OR_SKIP, // x4
[ 13] = _tag(UNIV, CONS, SET),
...
[ 15] = ASN1_OP_COND_FAIL,
where all four options are skippable and the second, third and fourth are
all conditional, as is the backstop at the end.
This hasn't been a problem so far because in the ASN.1 specs we have are
either using primitives or are using SET OF and SEQUENCE OF which are
handled correctly.
Whilst we're at it, also make sure that element labels get included in
comments in the output for elements that have complex types.
This cannot be tested with the code as it stands, but rather affects future
code.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-By: David Woodhouse <David.Woodhouse@intel.com>
The asn1_compiler process is particularly chatty and produces
about the only stdout output for an allmodconfig kernel.
In order to follow the general concept of 'no news is good
news' for building kernels, this hides all the existing output
unless the KBUILD_VERBOSE environment variable is set.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David Howells <dhowells@redhat.com>
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>
