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

[David Gibson]

On Mon, Aug 09, 2021 at 10:10:47AM -0300, Daniel Henrique Barboza wrote:
> 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)

Oof.. not necessarily a nack, but it would be nice to implement any
new instructions using the disastree path rather than the old ppc
specific decode logic.

> +{
> +    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

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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