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powerpc/bpf/jit: Fix/enhance 32-bit Load Immediate implementation 

The existing LI32() macro can sometimes result in a sign-extended 32-bit
load that does not clear the top 32-bits properly. As an example,
loading 0x7fffffff results in the register containing
0xffffffff7fffffff. While this does not impact classic BPF JIT
implementation (since that only uses the lower word for all operations),
we would like to share this macro between classic BPF JIT and extended
BPF JIT, wherein the entire 64-bit value in the register matters. Fix
this by first doing a shifted LI followed by ORI.

An additional optimization is with loading values between -32768 to -1,
where we now only need a single LI.

The new implementation now generates the same or less number of
instructions.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Naveen N. Rao 2016-06-22 21:55:02 +05:30 committed by Michael Ellerman
parent 5593e30327
commit aaf2f7e099
1 changed files with 10 additions and 3 deletions
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13
arch/powerpc/net/bpf_jit.h
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@ -232,10 +232,17 @@ DECLARE_LOAD_FUNC(sk_load_byte_msh);
(((cond) & 0x3ff) << 16) | \
(((dest) - (ctx->idx * 4)) & \
0xfffc))
#define PPC_LI32(d, i) do { PPC_LI(d, IMM_L(i)); \
if ((u32)(uintptr_t)(i) >= 32768) { \
PPC_ADDIS(d, d, IMM_HA(i)); \
/* Sign-extended 32-bit immediate load */
#define PPC_LI32(d, i) do { \
if ((int)(uintptr_t)(i) >= -32768 && \
(int)(uintptr_t)(i) < 32768) \
PPC_LI(d, i); \
else { \
PPC_LIS(d, IMM_H(i)); \
if (IMM_L(i)) \
PPC_ORI(d, d, IMM_L(i)); \
} } while(0)
#define PPC_LI64(d, i) do { \
if (!((uintptr_t)(i) & 0xffffffff00000000ULL)) \
PPC_LI32(d, i); \