[PATCH 09/19] PPC64/TCG: Implement 'rfebb' instruction

[Daniel Henrique Barboza <danielhb413@gmail.com>]

From: Gustavo Romero <gromero@linux.ibm.com>

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 EBB will:

- set the Global Enable (GE) bit of BESCR to 0;
- set bits 0-61 of the Event-Based Branch Return Register (EBBRR) to 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 next patches will use the remaining bits.

Note that we're implementing the extended rfebb mnemonic (BESCR_GE is
being always set to 1). The basic rfebb instruction would accept an
operand that would be used to set GE.

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

CC: Gustavo Romero <gustavo.romero@linaro.org>
Signed-off-by: Gustavo Romero <gromero@linux.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/cpu.h       | 12 ++++++++++++
 target/ppc/translate.c | 21 +++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index afd9cd402b..ae431e65be 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -358,6 +358,18 @@ typedef struct ppc_v3_pate_t {
 #define MMCR1_PMC3SEL PPC_BITMASK(48, 55)
 #define MMCR1_PMC4SEL PPC_BITMASK(56, 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)
+
 /* LPCR bits */
 #define LPCR_VPM0         PPC_BIT(0)
 #define LPCR_VPM1         PPC_BIT(1)
diff --git a/target/ppc/translate.c b/target/ppc/translate.c
index 62356cfadf..afc254a03f 100644
--- a/target/ppc/translate.c
+++ b/target/ppc/translate.c
@@ -2701,6 +2701,26 @@ static void gen_darn(DisasContext *ctx)
         }
     }
 }
+
+/* rfebb */
+static void gen_rfebb(DisasContext *ctx)
+{
+    TCGv target = tcg_temp_new();
+    TCGv bescr = tcg_temp_new();
+
+    gen_load_spr(target, SPR_EBBRR);
+    tcg_gen_mov_tl(cpu_nip, target);
+
+    gen_load_spr(bescr, SPR_BESCR);
+    tcg_gen_ori_tl(bescr, bescr, BESCR_GE);
+    gen_store_spr(SPR_BESCR, bescr);
+
+    ctx->base.is_jmp = DISAS_EXIT;
+
+    tcg_temp_free(target);
+    tcg_temp_free(bescr);
+}
+
 #endif
 
 /***                             Integer rotate                            ***/
@@ -7724,6 +7744,7 @@ 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(rfebb, 0x13, 0x12, 0x04, 0x03FFF001, PPC_NONE, PPC2_ISA207S),
 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
-- 
2.31.1