[PATCH v3 2/5] powerpc/lib/sstep: Add popcnt instruction emulation

[Matt Brown]

This adds emulations for the popcntb, popcntw, and popcntd instructions.
Tested for correctness against the popcnt{b,w,d} instructions on ppc64le.

Signed-off-by: Matt Brown <matthew.brown....@gmail.com>
---
v3:
        - optimised using the Giles-Miller method of side-ways addition
v2:
        - fixed opcodes
        - fixed typecasting
        - fixed bitshifting error for both 32 and 64bit arch
---
 arch/powerpc/lib/sstep.c | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 87d277f..c1f9cdb 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -612,6 +612,32 @@ static nokprobe_inline void do_cmpb(struct pt_regs *regs, 
unsigned long v1,
        regs->gpr[rd] = out_val;
 }
 
+/*
+ * The size parameter is used to adjust the equivalent popcnt instruction.
+ * popcntb = 8, popcntw = 32, popcntd = 64
+ */
+static nokprobe_inline void do_popcnt(struct pt_regs *regs, unsigned long v1,
+                               int size, int ra)
+{
+       unsigned long long out = v1;
+
+       out = (0x5555555555555555 & out) + (0x5555555555555555 & (out >> 1));
+       out = (0x3333333333333333 & out) + (0x3333333333333333 & (out >> 2));
+       out = (0x0f0f0f0f0f0f0f0f & out) + (0x0f0f0f0f0f0f0f0f & (out >> 4));
+       if (size == 8) {        /* popcntb */
+               regs->gpr[ra] = out;
+               return;
+       }
+       out = (0x001f001f001f001f & out) + (0x001f001f001f001f & (out >> 8));
+       out = (0x0000003f0000003f & out) + (0x0000003f0000003f & (out >> 16));
+       if (size == 32) {       /* popcntw */
+               regs->gpr[ra] = out;
+               return;
+       }
+       out = (0x000000000000007f & out) + (0x000000000000007f & (out >> 32));
+       regs->gpr[ra] = out;    /* popcntd */
+}
+
 static nokprobe_inline int trap_compare(long v1, long v2)
 {
        int ret = 0;
@@ -1194,6 +1220,10 @@ int analyse_instr(struct instruction_op *op, struct 
pt_regs *regs,
                        regs->gpr[ra] = regs->gpr[rd] & ~regs->gpr[rb];
                        goto logical_done;
 
+               case 122:       /* popcntb */
+                       do_popcnt(regs, regs->gpr[rd], 8, ra);
+                       goto logical_done;
+
                case 124:       /* nor */
                        regs->gpr[ra] = ~(regs->gpr[rd] | regs->gpr[rb]);
                        goto logical_done;
@@ -1206,6 +1236,10 @@ int analyse_instr(struct instruction_op *op, struct 
pt_regs *regs,
                        regs->gpr[ra] = regs->gpr[rd] ^ regs->gpr[rb];
                        goto logical_done;
 
+               case 378:       /* popcntw */
+                       do_popcnt(regs, regs->gpr[rd], 32, ra);
+                       goto logical_done;
+
                case 412:       /* orc */
                        regs->gpr[ra] = regs->gpr[rd] | ~regs->gpr[rb];
                        goto logical_done;
@@ -1217,7 +1251,11 @@ int analyse_instr(struct instruction_op *op, struct 
pt_regs *regs,
                case 476:       /* nand */
                        regs->gpr[ra] = ~(regs->gpr[rd] & regs->gpr[rb]);
                        goto logical_done;
-
+#ifdef __powerpc64__
+               case 506:       /* popcntd */
+                       do_popcnt(regs, regs->gpr[rd], 64, ra);
+                       goto logical_done;
+#endif
                case 922:       /* extsh */
                        regs->gpr[ra] = (signed short) regs->gpr[rd];
                        goto logical_done;
-- 
2.9.3