d66423fbe1
As Alexei points out, struct bpf_sk_lookup_kern has two 4-byte holes.
This leads to suboptimal instructions being generated (IPv4, x86):
1372 struct bpf_sk_lookup_kern ctx = {
0xffffffff81b87f30 <+624>: xor %eax,%eax
0xffffffff81b87f32 <+626>: mov $0x6,%ecx
0xffffffff81b87f37 <+631>: lea 0x90(%rsp),%rdi
0xffffffff81b87f3f <+639>: movl $0x110002,0x88(%rsp)
0xffffffff81b87f4a <+650>: rep stos %rax,%es:(%rdi)
0xffffffff81b87f4d <+653>: mov 0x8(%rsp),%eax
0xffffffff81b87f51 <+657>: mov %r13d,0x90(%rsp)
0xffffffff81b87f59 <+665>: incl %gs:0x7e4970a0(%rip)
0xffffffff81b87f60 <+672>: mov %eax,0x8c(%rsp)
0xffffffff81b87f67 <+679>: movzwl 0x10(%rsp),%eax
0xffffffff81b87f6c <+684>: mov %ax,0xa8(%rsp)
0xffffffff81b87f74 <+692>: movzwl 0x38(%rsp),%eax
0xffffffff81b87f79 <+697>: mov %ax,0xaa(%rsp)
Fix this by moving around sport and dport. pahole confirms there
are no more holes:
struct bpf_sk_lookup_kern {
u16 family; /* 0 2 */
u16 protocol; /* 2 2 */
__be16 sport; /* 4 2 */
u16 dport; /* 6 2 */
struct {
__be32 saddr; /* 8 4 */
__be32 daddr; /* 12 4 */
} v4; /* 8 8 */
struct {
const struct in6_addr * saddr; /* 16 8 */
const struct in6_addr * daddr; /* 24 8 */
} v6; /* 16 16 */
struct sock * selected_sk; /* 32 8 */
bool no_reuseport; /* 40 1 */
/* size: 48, cachelines: 1, members: 8 */
/* padding: 7 */
/* last cacheline: 48 bytes */
};
The assembly also doesn't contain the pesky rep stos anymore:
1372 struct bpf_sk_lookup_kern ctx = {
0xffffffff81b87f60 <+624>: movzwl 0x10(%rsp),%eax
0xffffffff81b87f65 <+629>: movq $0x0,0xa8(%rsp)
0xffffffff81b87f71 <+641>: movq $0x0,0xb0(%rsp)
0xffffffff81b87f7d <+653>: mov %ax,0x9c(%rsp)
0xffffffff81b87f85 <+661>: movzwl 0x38(%rsp),%eax
0xffffffff81b87f8a <+666>: movq $0x0,0xb8(%rsp)
0xffffffff81b87f96 <+678>: mov %ax,0x9e(%rsp)
0xffffffff81b87f9e <+686>: mov 0x8(%rsp),%eax
0xffffffff81b87fa2 <+690>: movq $0x0,0xc0(%rsp)
0xffffffff81b87fae <+702>: movl $0x110002,0x98(%rsp)
0xffffffff81b87fb9 <+713>: mov %eax,0xa0(%rsp)
0xffffffff81b87fc0 <+720>: mov %r13d,0xa4(%rsp)
1: https://lore.kernel.org/bpf/CAADnVQKE6y9h2fwX6OS837v-Uf+aBXnT_JXiN_bbo2gitZQ3tA@mail.gmail.com/
Fixes: e9ddbb7707ff ("bpf: Introduce SK_LOOKUP program type with a dedicated attach point")
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Link: https://lore.kernel.org/bpf/20200910110248.198326-1-lmb@cloudflare.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.