Mind all-zeroes mask in gen_mcmp().

[libpcap] / gencode.c

diff --git a/gencode.c b/gencode.c
index af3e0945b774f93e6b4a095f58052325959432aa..d36abbeb52d6197b48d64e83485b40ae98bd90cd 100644 (file)
--- a/gencode.c
+++ b/gencode.c
@@ -1459,6 +1459,19 @@ static struct block *
 gen_mcmp(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
     u_int size, bpf_u_int32 v, bpf_u_int32 mask)
 {
+       /*
+        * For any A: if mask == 0, it means A & mask == 0, so the result is
+        * true iff v == 0.  In this case ideally the caller should have
+        * skipped this invocation and have fewer statement blocks to juggle.
+        * If the caller could have skipped, but has not, produce a block with
+        * fewer statements.
+        *
+        * This could be done in gen_ncmp() in a more generic way, but this
+        * function is the only code path that can have mask == 0.
+        */
+       if (mask == 0)
+               return v ? gen_false(cstate) : gen_true(cstate);
+
        return gen_ncmp(cstate, offrel, offset, size, mask, BPF_JEQ, 0, v);
 }