target-ppc: implement darn instruction

darn: Deliver A Random Number

Currently return invalid random number for all the case. This needs
proper algorithm to provide cryptographically suitable random data.
Reading from /dev/random can block and that is not an expected behaviour
while the cpu instruction is getting executed. Moreover, /dev/random
would only work for linux-user

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
[dwg: Added minor clang warning fix for ppc32 target]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target-ppc/helper.h

@@ -50,6 +50,8 @@ DEF_HELPER_FLAGS_1(cnttzd, TCG_CALL_NO_RWG_SE, tl, tl)
 DEF_HELPER_FLAGS_1(popcntd, TCG_CALL_NO_RWG_SE, tl, tl)
 DEF_HELPER_FLAGS_2(bpermd, TCG_CALL_NO_RWG_SE, i64, i64, i64)
 DEF_HELPER_3(srad, tl, env, tl, tl)
+DEF_HELPER_0(darn32, tl)
+DEF_HELPER_0(darn64, tl)
 #endif
 
 DEF_HELPER_FLAGS_1(cntlsw32, TCG_CALL_NO_RWG_SE, i32, i32)

target-ppc/int_helper.c

@@ -182,6 +182,22 @@ target_ulong helper_cnttzd(target_ulong t)
 {
     return ctz64(t);
 }
+
+/* Return invalid random number.
+ *
+ * FIXME: Add rng backend or other mechanism to get cryptographically suitable
+ * random number
+ */
+target_ulong helper_darn32(void)
+{
+    return -1;
+}
+
+target_ulong helper_darn64(void)
+{
+    return -1;
+}
+
 #endif
 
 #if defined(TARGET_PPC64)

target-ppc/translate.c

@@ -528,6 +528,10 @@ EXTRACT_HELPER(FPW, 16, 1);
 
 /* addpcis */
 EXTRACT_HELPER_DXFORM(DX, 10, 6, 6, 5, 16, 1, 1, 0, 0)
+#if defined(TARGET_PPC64)
+/* darn */
+EXTRACT_HELPER(L, 16, 2);
+#endif
 
 /***                            Jump target decoding                       ***/
 /* Immediate address */
@@ -1895,6 +1899,21 @@ static void gen_cnttzd(DisasContext *ctx)
         gen_set_Rc0(ctx, cpu_gpr[rA(ctx->opcode)]);
     }
 }
+
+/* darn */
+static void gen_darn(DisasContext *ctx)
+{
+    int l = L(ctx->opcode);
+
+    if (l == 0) {
+        gen_helper_darn32(cpu_gpr[rD(ctx->opcode)]);
+    } else if (l <= 2) {
+        /* Return 64-bit random for both CRN and RRN */
+        gen_helper_darn64(cpu_gpr[rD(ctx->opcode)]);
+    } else {
+        tcg_gen_movi_i64(cpu_gpr[rD(ctx->opcode)], -1);
+    }
+}
 #endif
 
 /***                             Integer rotate                            ***/
@@ -6216,6 +6235,7 @@ GEN_HANDLER_E(prtyw, 0x1F, 0x1A, 0x04, 0x0000F801, PPC_NONE, PPC2_ISA205),
 GEN_HANDLER(popcntd, 0x1F, 0x1A, 0x0F, 0x0000F801, PPC_POPCNTWD),
 GEN_HANDLER(cntlzd, 0x1F, 0x1A, 0x01, 0x00000000, PPC_64B),
 GEN_HANDLER_E(cnttzd, 0x1F, 0x1A, 0x11, 0x00000000, PPC_NONE, PPC2_ISA300),
+GEN_HANDLER_E(darn, 0x1F, 0x13, 0x17, 0x001CF801, PPC_NONE, PPC2_ISA300),
 GEN_HANDLER_E(prtyd, 0x1F, 0x1A, 0x05, 0x0000F801, PPC_NONE, PPC2_ISA205),
 GEN_HANDLER_E(bpermd, 0x1F, 0x1C, 0x07, 0x00000001, PPC_NONE, PPC2_PERM_ISA206),
 #endif