Re: [PATCH v36 04/17] target/avr: Add instruction translation - Registers definition

[Aleksandar Markovic]

On Sun, Nov 24, 2019 at 6:03 AM Michael Rolnik <address@hidden> wrote:
>
> Signed-off-by: Michael Rolnik <address@hidden>
> ---
>  target/avr/translate.c | 132 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 132 insertions(+)
>  create mode 100644 target/avr/translate.c
>
> diff --git a/target/avr/translate.c b/target/avr/translate.c
> new file mode 100644
> index 0000000000..53c9892a60
> --- /dev/null
> +++ b/target/avr/translate.c
> @@ -0,0 +1,132 @@
> +/*
> + * QEMU AVR CPU
> + *
> + * Copyright (c) 2019 Michael Rolnik
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, see
> + * <http://www.gnu.org/licenses/lgpl-2.1.html>
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/qemu-print.h"
> +#include "tcg/tcg.h"
> +#include "cpu.h"
> +#include "exec/exec-all.h"
> +#include "disas/disas.h"
> +#include "tcg-op.h"
> +#include "exec/cpu_ldst.h"
> +#include "exec/helper-proto.h"
> +#include "exec/helper-gen.h"
> +#include "exec/log.h"
> +#include "exec/gdbstub.h"
> +#include "exec/translator.h"
> +#include "exec/gen-icount.h"
> +
> +/*
> + *  Define if you want a BREAK instruction translated to a breakpoint
> + *  Active debugging connection is assumed
> + *  This is for
> + *  https://github.com/seharris/qemu-avr-tests/tree/master/instruction-tests
> + *  tests
> + */
> +#undef BREAKPOINT_ON_BREAK
> +
> +static TCGv cpu_pc;
> +
> +static TCGv cpu_Cf;
> +static TCGv cpu_Zf;
> +static TCGv cpu_Nf;
> +static TCGv cpu_Vf;
> +static TCGv cpu_Sf;
> +static TCGv cpu_Hf;
> +static TCGv cpu_Tf;
> +static TCGv cpu_If;
> +
> +static TCGv cpu_rampD;
> +static TCGv cpu_rampX;
> +static TCGv cpu_rampY;
> +static TCGv cpu_rampZ;
> +
> +static TCGv cpu_r[NO_CPU_REGISTERS];
> +static TCGv cpu_eind;
> +static TCGv cpu_sp;
> +
> +static TCGv cpu_skip;
> +
> +static const char reg_names[NO_CPU_REGISTERS][8] = {
> +    "r0",  "r1",  "r2",  "r3",  "r4",  "r5",  "r6",  "r7",
> +    "r8",  "r9",  "r10", "r11", "r12", "r13", "r14", "r15",
> +    "r16", "r17", "r18", "r19", "r20", "r21", "r22", "r23",
> +    "r24", "r25", "r26", "r27", "r28", "r29", "r30", "r31",
> +};
> +#define REG(x) (cpu_r[x])
> +
> +enum {
> +    DISAS_EXIT   = DISAS_TARGET_0,  /* We want return to the cpu main loop.  
> */
> +    DISAS_LOOKUP = DISAS_TARGET_1,  /* We have a variable condition exit.  */
> +    DISAS_CHAIN  = DISAS_TARGET_2,  /* We have a single condition exit.  */
> +};
> +
> +typedef struct DisasContext DisasContext;
> +
> +/* This is the state at translation time. */
> +struct DisasContext {
> +    TranslationBlock *tb;
> +
> +    CPUAVRState *env;
> +    CPUState *cs;
> +
> +    target_long npc;
> +    uint32_t opcode;
> +
> +    /* Routine used to access memory */
> +    int memidx;
> +    int bstate;
> +    int singlestep;
> +
> +    TCGv skip_var0;
> +    TCGv skip_var1;
> +    TCGCond skip_cond;
> +    bool free_skip_var0;

This set of four lines are by far the hardest to connect to the documentation.

Please add before them a sizable comment with explanations for:

- the reson these variables are introduced
- why are they here (part of DisasContext)
- what they affect
- summary of the way they work

Perhaps add comments to other places where "skip"-related data fields
are introduced.

(I believe the implementation is correct, but it is extremely hard to the reader
to reverse-engineer the intentions)

Yours,
Aleksandar

> +};
> +
> +static int to_A(DisasContext *ctx, int indx) { return 16 + (indx % 16); }
> +static int to_B(DisasContext *ctx, int indx) { return 16 + (indx % 8); }
> +static int to_C(DisasContext *ctx, int indx) { return 24 + (indx % 4) * 2; }
> +static int to_D(DisasContext *ctx, int indx) { return (indx % 16) * 2; }
> +
> +static uint16_t next_word(DisasContext *ctx)
> +{
> +    return cpu_lduw_code(ctx->env, ctx->npc++ * 2);
> +}
> +
> +static int append_16(DisasContext *ctx, int x)
> +{
> +    return x << 16 | next_word(ctx);
> +}
> +
> +
> +static bool avr_have_feature(DisasContext *ctx, int feature)
> +{
> +    if (!avr_feature(ctx->env, feature)) {
> +        gen_helper_unsupported(cpu_env);
> +        ctx->bstate = DISAS_NORETURN;
> +        return false;
> +    }
> +    return true;
> +}
> +
> +static bool decode_insn(DisasContext *ctx, uint16_t insn);
> +#include "decode_insn.inc.c"
> +
> --
> 2.17.2 (Apple Git-113)
>