PPC64/TCG: Implement 'rfebb' instruction

An Event-Based Branch (EBB) allows applications to change the NIA when a
event-based exception occurs. Event-based exceptions are enabled by
setting the Branch Event Status and Control Register (BESCR). If the
event-based exception is enabled when the exception occurs, an EBB
happens.

The following operations happens during an EBB:

- Global Enable (GE) bit of BESCR is set to 0;
- bits 0-61 of the Event-Based Branch Return Register (EBBRR) are set
to the the effective address of the NIA that would have executed if the EBB
didn't happen;
- Instruction fetch and execution will continue in the effective address
contained in the Event-Based Branch Handler Register (EBBHR).

The EBB Handler will process the event and then execute the Return From
Event-Based Branch (rfebb) instruction. rfebb sets BESCR_GE and then
redirects execution to the address pointed in EBBRR. This process is
described in the PowerISA v3.1, Book II, Chapter 6 [1].

This patch implements the rfebb instruction. Descriptions of all
relevant BESCR bits are also added - this patch is only using BESCR_GE,
but the next patches will use the remaining bits.

[1] https://wiki.raptorcs.com/w/images/f/f5/PowerISA_public.v3.1.pdf

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20211201151734.654994-9-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

target/ppc/cpu.h

@@ -392,6 +392,19 @@ typedef enum {
 /* PMU uses CTRL_RUN to sample PM_RUN_INST_CMPL */
 #define CTRL_RUN PPC_BIT(63)
 
+/* EBB/BESCR bits */
+/* Global Enable */
+#define BESCR_GE PPC_BIT(0)
+/* External Event-based Exception Enable */
+#define BESCR_EE PPC_BIT(30)
+/* Performance Monitor Event-based Exception Enable */
+#define BESCR_PME PPC_BIT(31)
+/* External Event-based Exception Occurred */
+#define BESCR_EEO PPC_BIT(62)
+/* Performance Monitor Event-based Exception Occurred */
+#define BESCR_PMEO PPC_BIT(63)
+#define BESCR_INVALID PPC_BITMASK(32, 33)
+
 /* LPCR bits */
 #define LPCR_VPM0         PPC_BIT(0)
 #define LPCR_VPM1         PPC_BIT(1)

target/ppc/excp_helper.c

@@ -1228,6 +1228,37 @@ void helper_hrfid(CPUPPCState *env)
 }
 #endif
 
+#if defined(TARGET_PPC64) && !defined(CONFIG_USER_ONLY)
+void helper_rfebb(CPUPPCState *env, target_ulong s)
+{
+    target_ulong msr = env->msr;
+
+    /*
+     * Handling of BESCR bits 32:33 according to PowerISA v3.1:
+     *
+     * "If BESCR 32:33 != 0b00 the instruction is treated as if
+     *  the instruction form were invalid."
+     */
+    if (env->spr[SPR_BESCR] & BESCR_INVALID) {
+        raise_exception_err(env, POWERPC_EXCP_PROGRAM,
+                            POWERPC_EXCP_INVAL | POWERPC_EXCP_INVAL_INVAL);
+    }
+
+    env->nip = env->spr[SPR_EBBRR];
+
+    /* Switching to 32-bit ? Crop the nip */
+    if (!msr_is_64bit(env, msr)) {
+        env->nip = (uint32_t)env->spr[SPR_EBBRR];
+    }
+
+    if (s) {
+        env->spr[SPR_BESCR] |= BESCR_GE;
+    } else {
+        env->spr[SPR_BESCR] &= ~BESCR_GE;
+    }
+}
+#endif
+
 /*****************************************************************************/
 /* Embedded PowerPC specific helpers */
 void helper_40x_rfci(CPUPPCState *env)

target/ppc/helper.h

@@ -18,6 +18,7 @@ DEF_HELPER_2(pminsn, void, env, i32)
 DEF_HELPER_1(rfid, void, env)
 DEF_HELPER_1(rfscv, void, env)
 DEF_HELPER_1(hrfid, void, env)
+DEF_HELPER_2(rfebb, void, env, tl)
 DEF_HELPER_2(store_lpcr, void, env, tl)
 DEF_HELPER_2(store_pcr, void, env, tl)
 DEF_HELPER_2(store_mmcr0, void, env, tl)

target/ppc/insn32.decode

@@ -470,3 +470,8 @@ XSMINJDP        111100 ..... ..... ..... 10011000 ...   @XX3
 ## VSX Binary Floating-Point Convert Instructions
 
 XSCVQPDP        111111 ..... 10100 ..... 1101000100 .   @X_tb_rc
+
+### rfebb
+&XL_s           s:uint8_t
+@XL_s           ......-------------- s:1 .......... -   &XL_s
+RFEBB           010011-------------- .   0010010010 -   @XL_s

target/ppc/translate.c

@@ -7461,6 +7461,8 @@ static bool resolve_PLS_D(DisasContext *ctx, arg_D *d, arg_PLS_D *a)
 
 #include "translate/spe-impl.c.inc"
 
+#include "translate/branch-impl.c.inc"
+
 /* Handles lfdp, lxsd, lxssp */
 static void gen_dform39(DisasContext *ctx)
 {

target/ppc/translate/branch-impl.c.inc

@@ -0,0 +1,33 @@
+/*
+ * Power ISA decode for branch instructions
+ *
+ *  Copyright IBM Corp. 2021
+ *
+ * Authors:
+ *  Daniel Henrique Barboza      <danielhb413@gmail.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#if defined(TARGET_PPC64) && !defined(CONFIG_USER_ONLY)
+
+static bool trans_RFEBB(DisasContext *ctx, arg_XL_s *arg)
+{
+    REQUIRE_INSNS_FLAGS2(ctx, ISA207S);
+
+    gen_icount_io_start(ctx);
+    gen_update_cfar(ctx, ctx->cia);
+    gen_helper_rfebb(cpu_env, cpu_gpr[arg->s]);
+
+    ctx->base.is_jmp = DISAS_CHAIN;
+
+    return true;
+}
+#else
+static bool trans_RFEBB(DisasContext *ctx, arg_XL_s *arg)
+{
+    gen_invalid(ctx);
+    return true;
+}
+#endif