| |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
In line with similar support for other architectures by Daniel Borkmann.
'MOD Default X' from test_bpf without constant blinding:
84 bytes emitted from JIT compiler (pass:3, flen:7)
d0000000058a4688 + <x>:
0: nop
4: nop
8: std r27,-40(r1)
c: std r28,-32(r1)
10: xor r8,r8,r8
14: xor r28,r28,r28
18: mr r27,r3
1c: li r8,66
20: cmpwi r28,0
24: bne 0x0000000000000030
28: li r8,0
2c: b 0x0000000000000044
30: divwu r9,r8,r28
34: mullw r9,r28,r9
38: subf r8,r9,r8
3c: rotlwi r8,r8,0
40: li r8,66
44: ld r27,-40(r1)
48: ld r28,-32(r1)
4c: mr r3,r8
50: blr
... and with constant blinding:
140 bytes emitted from JIT compiler (pass:3, flen:11)
d00000000bd6ab24 + <x>:
0: nop
4: nop
8: std r27,-40(r1)
c: std r28,-32(r1)
10: xor r8,r8,r8
14: xor r28,r28,r28
18: mr r27,r3
1c: lis r2,-22834
20: ori r2,r2,36083
24: rotlwi r2,r2,0
28: xori r2,r2,36017
2c: xoris r2,r2,42702
30: rotlwi r2,r2,0
34: mr r8,r2
38: rotlwi r8,r8,0
3c: cmpwi r28,0
40: bne 0x000000000000004c
44: li r8,0
48: b 0x000000000000007c
4c: divwu r9,r8,r28
50: mullw r9,r28,r9
54: subf r8,r9,r8
58: rotlwi r8,r8,0
5c: lis r2,-17137
60: ori r2,r2,39065
64: rotlwi r2,r2,0
68: xori r2,r2,39131
6c: xoris r2,r2,48399
70: rotlwi r2,r2,0
74: mr r8,r2
78: rotlwi r8,r8,0
7c: ld r27,-40(r1)
80: ld r28,-32(r1)
84: mr r3,r8
88: blr
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
|
| |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
Tail calls allow JIT'ed eBPF programs to call into other JIT'ed eBPF
programs. This can be achieved either by:
(1) retaining the stack setup by the first eBPF program and having all
subsequent eBPF programs re-using it, or,
(2) by unwinding/tearing down the stack and having each eBPF program
deal with its own stack as it sees fit.
To ensure that this does not create loops, there is a limit to how many
tail calls can be done (currently 32). This requires the JIT'ed code to
maintain a count of the number of tail calls done so far.
Approach (1) is simple, but requires every eBPF program to have (almost)
the same prologue/epilogue, regardless of whether they need it. This is
inefficient for small eBPF programs which may not sometimes need a
prologue at all. As such, to minimize impact of tail call
implementation, we use approach (2) here which needs each eBPF program
in the chain to use its own prologue/epilogue. This is not ideal when
many tail calls are involved and when all the eBPF programs in the chain
have similar prologue/epilogue. However, the impact is restricted to
programs that do tail calls. Individual eBPF programs are not affected.
We maintain the tail call count in a fixed location on the stack and
updated tail call count values are passed in through this. The very
first eBPF program in a chain sets this up to 0 (the first 2
instructions). Subsequent tail calls skip the first two eBPF JIT
instructions to maintain the count. For programs that don't do tail
calls themselves, the first two instructions are NOPs.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
|
