bpf: do not use reciprocal divide
At first Jakub Zawadzki noticed that some divisions by reciprocal_divide
were not correct. (off by one in some cases)
http://www.wireshark.org/~darkjames/reciprocal-buggy.c
He could also show this with BPF:
http://www.wireshark.org/~darkjames/set-and-dump-filter-k-bug.c
The reciprocal divide in linux kernel is not generic enough,
lets remove its use in BPF, as it is not worth the pain with
current cpus.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Cc: Mircea Gherzan <mgherzan@gmail.com>
Cc: Daniel Borkmann <dxchgb@gmail.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Matt Evans <matt@ozlabs.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
index 218b6b2..01fe994 100644
--- a/arch/sparc/net/bpf_jit_comp.c
+++ b/arch/sparc/net/bpf_jit_comp.c
@@ -497,9 +497,20 @@
case BPF_S_ALU_MUL_K: /* A *= K */
emit_alu_K(MUL, K);
break;
- case BPF_S_ALU_DIV_K: /* A /= K */
- emit_alu_K(MUL, K);
- emit_read_y(r_A);
+ case BPF_S_ALU_DIV_K: /* A /= K with K != 0*/
+ if (K == 1)
+ break;
+ emit_write_y(G0);
+#ifdef CONFIG_SPARC32
+ /* The Sparc v8 architecture requires
+ * three instructions between a %y
+ * register write and the first use.
+ */
+ emit_nop();
+ emit_nop();
+ emit_nop();
+#endif
+ emit_alu_K(DIV, K);
break;
case BPF_S_ALU_DIV_X: /* A /= X; */
emit_cmpi(r_X, 0);