diff options
| -rw-r--r-- | optimize.c | 32 |
1 files changed, 30 insertions, 2 deletions
@@ -745,11 +745,39 @@ fold_op(compiler_state_t *cstate, opt_state_t *opt_state, break; case BPF_LSH: - a <<= b; + /* + * A left shift of more than the width of the type + * is undefined in C; we'll just treat it as shifting + * all the bits out. + * + * XXX - the BPF interpreter doesn't check for this, + * so its behavior is dependent on the behavior of + * the processor on which it's running. There are + * processors on which it shifts all the bits out + * and processors on which it does no shift. + */ + if (b < 32) + a <<= b; + else + a = 0; break; case BPF_RSH: - a >>= b; + /* + * A right shift of more than the width of the type + * is undefined in C; we'll just treat it as shifting + * all the bits out. + * + * XXX - the BPF interpreter doesn't check for this, + * so its behavior is dependent on the behavior of + * the processor on which it's running. There are + * processors on which it shifts all the bits out + * and processors on which it does no shift. + */ + if (b < 32) + a >>= b; + else + a = 0; break; default: |