Messages in this thread | | | Date | Tue, 19 Jan 2010 14:35:20 -0500 | From | William Allen Simpson <> | Subject | Re: [PATCH v2] tcp: input header length, prediction, and timestamp bugs |
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William Allen Simpson wrote: > Therefore, I'll resubmit this patch, removing the existing len parameter. > And maybe *th, too.... > Just to quickly note that gcc 4.4 doesn't properly remember that it has already loaded *th with this rampant use of an inline function (unlike the older macro method):
c04ea739: 89 d3 mov %edx,%ebx
static inline struct tcphdr *tcp_hdr(const struct sk_buff *skb) { return (struct tcphdr *)skb_transport_header(skb); c04ea743: 8b 92 94 00 00 00 mov 0x94(%edx),%edx * * Our current scheme is not silly either but we take the * extra cost of the net_bh soft interrupt processing... * We do checksum and copy also but from device to kernel. */ if ((tcp_flag_word(tcp_hdr(skb)) & TCP_HP_BITS) == tp->pred_flags && ...
Note that the index is in both %edx and %ebx, but it uses replaced %edx. Although by inspection that result stays in %edx, it reloaded twice more:
res = tcp_validate_incoming(sk, skb, tcp_hdr(skb), 1); c04ea78c: 8b 8b 94 00 00 00 mov 0x94(%ebx),%ecx c04ea792: 89 da mov %ebx,%edx c04ea794: 89 f0 mov %esi,%eax c04ea796: c7 04 24 01 00 00 00 movl $0x1,(%esp) c04ea79d: e8 0e c3 ff ff call c04e6ab0 <tcp_validate_incoming> if (res <= 0) c04ea7a2: 85 c0 test %eax,%eax c04ea7a4: 0f 8e 8e 03 00 00 jle c04eab38 <tcp_rcv_established+0x408>
#else /* NET_SKBUFF_DATA_USES_OFFSET */
static inline unsigned char *skb_transport_header(const struct sk_buff *skb) { return skb->transport_header; c04ea7aa: 8b 83 94 00 00 00 mov 0x94(%ebx),%eax c04ea7b0: f6 40 0d 10 testb $0x10,0xd(%eax) c04ea7b4: 0f 85 5e 03 00 00 jne c04eab18 <tcp_rcv_established+0x3e8>
This doesn't happen with the parameter *th (undisturbed in %edi):
c04ea78a: 89 f9 mov %edi,%ecx c04ea78c: 89 f2 mov %esi,%edx c04ea78e: 89 d8 mov %ebx,%eax c04ea790: c7 04 24 01 00 00 00 movl $0x1,(%esp) c04ea797: e8 14 c3 ff ff call c04e6ab0 <tcp_validate_incoming> if (res <= 0) c04ea79c: 85 c0 test %eax,%eax c04ea79e: 0f 8e 8c 03 00 00 jle c04eab30 <tcp_rcv_established+0x400> return -res;
step5: if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0) c04ea7a4: f6 47 0d 10 testb $0x10,0xd(%edi) c04ea7a8: 0f 85 62 03 00 00 jne c04eab10 <tcp_rcv_established+0x3e0>
Therefore, keeping the parameter *th.
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