Re: [PATCHv2, 2/7] ppc: bpf/jit: Fix/enhance 32-bit Load Immediate implementation

[Michael Ellerman]

On Wed, 2016-22-06 at 16:25:02 UTC, "Naveen N. Rao" wrote:
> 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 0x7fff results in the register containing
> 0x7fff. 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 
> Signed-off-by: Naveen N. Rao 

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/aaf2f7e09932a08c1287d8e4c6

cheers

[PATCHv2 2/7] ppc: bpf/jit: Fix/enhance 32-bit Load Immediate implementation

[Naveen N. Rao]

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 0x7fff results in the register containing
0x7fff. 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.

Cc: Matt Evans 
Cc: Denis Kirjanov 
Cc: Michael Ellerman 
Cc: Paul Mackerras 
Cc: Alexei Starovoitov 
Cc: Daniel Borkmann 
Cc: "David S. Miller" 
Cc: Ananth N Mavinakayanahalli 
Cc: Thadeu Lima de Souza Cascardo 
Acked-by: Alexei Starovoitov 
Signed-off-by: Naveen N. Rao 
---
 arch/powerpc/net/bpf_jit.h | 13 ++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 889fd19..a9882db 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -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) & 0xULL))\
PPC_LI32(d, i);   \
-- 
2.8.2