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| author | Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> | 2016-09-24 02:05:01 +0530 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2016-10-04 20:33:19 +1100 |
| commit | ce0761419faefbe9e450749ccc879ff88843af12 (patch) | |
| tree | e11d3ae238cd82b7d59274f0491c9ca5f47e8e63 /arch/powerpc/include/asm | |
| parent | 7b847f523fe07b4ad73a01cec49a4da86a9be412 (diff) | |
| download | linux-ce0761419faefbe9e450749ccc879ff88843af12.tar.gz linux-ce0761419faefbe9e450749ccc879ff88843af12.tar.bz2 linux-ce0761419faefbe9e450749ccc879ff88843af12.zip | |
powerpc/bpf: Implement support for tail calls
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>
Diffstat (limited to 'arch/powerpc/include/asm')
| -rw-r--r-- | arch/powerpc/include/asm/ppc-opcode.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h index 127ebf5862b4..54ff8ce7fa96 100644 --- a/arch/powerpc/include/asm/ppc-opcode.h +++ b/arch/powerpc/include/asm/ppc-opcode.h @@ -236,6 +236,7 @@ #define PPC_INST_STWU 0x94000000 #define PPC_INST_MFLR 0x7c0802a6 #define PPC_INST_MTLR 0x7c0803a6 +#define PPC_INST_MTCTR 0x7c0903a6 #define PPC_INST_CMPWI 0x2c000000 #define PPC_INST_CMPDI 0x2c200000 #define PPC_INST_CMPW 0x7c000000 @@ -250,6 +251,7 @@ #define PPC_INST_SUB 0x7c000050 #define PPC_INST_BLR 0x4e800020 #define PPC_INST_BLRL 0x4e800021 +#define PPC_INST_BCTR 0x4e800420 #define PPC_INST_MULLD 0x7c0001d2 #define PPC_INST_MULLW 0x7c0001d6 #define PPC_INST_MULHWU 0x7c000016 |