Re: [PATCH v32 04/13] target/avr: Add instruction translation - Registers definition

[Aleksandar Markovic]

On Friday, October 18, 2019, Aleksandar Markovic <address@hidden> wrote:

On Friday, October 18, 2019, Michael Rolnik <address@hidden> wrote:

On Fri, Oct 18, 2019 at 4:23 PM Aleksandar Markovic
<address@hidden> wrote:
>
>
>
> On Friday, October 18, 2019, Michael Rolnik <address@hidden> wrote:
>>
>>
>>
>> On Fri, Oct 18, 2019 at 11:52 AM Aleksandar Markovic <address@hidden> wrote:
>>>
>>>
>>>
>>> On Thursday, October 17, 2019, Michael Rolnik <address@hidden> wrote:
>>>>
>>>> On Thu, Oct 17, 2019 at 11:17 PM Aleksandar Markovic
>>>> <address@hidden> wrote:
>>>> >>
>>>> >>
>>>> >> >> +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;
>>>> >> >> +
>>>> >> >
>>>> >> >
>>>> >> > Hello, Michael,
>>>> >> >
>>>> >> > Is there any particular reason or motivation beyond modelling status register flags as TCGv variables?
>>>> >>
>>>> >>
>>>> >>
>>>> >> I think it's easier this way as I don't need to convert flag values to
>>>> >> bits or bits to flag values.
>>>> >
>>>> >
>>>> > Ok. But, how do you map 0/1 flag value to the value of a TCGv variable and vice versa? In other words, what value or values (out of 2^32 vales) of a TCGv variable mean the flag is 1? And the same question for 0.
>>>> >
>>>> > Is 0110000111000010100 one or zero?
>>>> >
>>>> > Besides, in such arrangement, how do you display the 8-bit status register in gdb, if at all?
>>>>
>>>> each flag register is either 0 or 1,....
>>>>
>>>>
>>>>
>>>
>>> Michael,
>>>
>>> If this is true, why is there a special handling of two flags in the following code:
>>>
>>>
>>> static inline uint8_t cpu_get_sreg(CPUAVRState *env)
>>> {
>>> uint8_t sreg;
>>> sreg = (env->sregC & 0x01) << 0
>>> | (env->sregZ == 0 ? 1 : 0) << 1
>>> | (env->sregN) << 2
>>> | (env->sregV) << 3
>>> | (env->sregS) << 4
>>> | (env->sregH) << 5
>>> | (env->sregT) << 6
>>> | (env->sregI) << 7;
>>> return sreg;
>>> }
>>> static inline void cpu_set_sreg(CPUAVRState *env, uint8_t sreg)
>>> {
>>> env->sregC = (sreg >> 0) & 0x01;
>>> env->sregZ = (sreg >> 1) & 0x01 ? 0 : 1;
>>> env->sregN = (sreg >> 2) & 0x01;
>>> env->sregV = (sreg >> 3) & 0x01;
>>> env->sregS = (sreg >> 4) & 0x01;
>>> env->sregH = (sreg >> 5) & 0x01;
>>> env->sregT = (sreg >> 6) & 0x01;
>>> env->sregI = (sreg >> 7) & 0x01;
>>> }
>>>  ?
>>>
>> Aleksandar,
>>
>> If I understand your question correctly cpu_get_sreg assembles SREG value to be presented by GDB, and cpu_set_sreg sets flags values when GDB modifies SREG.
>>
>> Michael
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>
>
> 

Why is handling of sregC and sregZ flags different than handling of other flags? This contradicts your previos statement that 1 (in TCGv) means 1 (flag), and 0 (in TCGv) means 0 (flag)?
>
>
> Whatever is the explanation, ot should be included, in my opinion, in code comments.
>
> Please, Michael, let's first clarify the issue from the question above.
>
> Thanks, Aleksandar
>
>
there is a comment here
https://github.com/michaelrolnik/qemu-avr/blob/master/target/avr/cpu.h#L122-L129
>

...but it does explain WHY of my question.

I meant to say  "does not", not "does".

Michael, don't be discouraged by lenghty review process, just be persistent and available for communication with reviewers.

Sincerely,

Aleksandar

 

The reason I insist on your explanation is that when we model a cpu or a device in QEMU, a goal is that the model is as close to the hardware as possible. One may not, for pletora of reasons, succeed in reaching that goal, or, I can imagine, on purpose depart from that goal for some reason - perhaps that was the case in your implementation, where you modelled a single 8-bit status register with 8 TCGv variables.

But, even that way of modelling was done inconsistently across bits of the status register. In that light, I want to know the justification for that, so repeat my question: Why is handling of sregC and sregZ flags different than handling of other flags in functions cpu_get_sreg() and cpu_get_sreg()? This was not explained in any comment or commit message. And is in contradiction with one of your previous answers.

Yours,

Aleksandar

 

>
>
>>>
>>> Thanks,
>>> A.
>>>>
>>>>
>>>>  they are calculated here
>>>> 1. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/translate.c#L146-L148
>>>> 2. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/translate.c#L166
>>>> 3. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/translate.c#L185-L187
>>>> 4. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/translate.c#L205
>>>> 5. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/translate.c#L214-L215
>>>> 6. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/translate.c#L222-L223
>>>> The COU itself never uses SREG at all, only the flags.
>>>>
>>>> As for the GDB it's get assembled/disassembled here
>>>> 1. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/cpu.h#L219-L243
>>>> 2. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/gdbstub.c#L35-L37
>>>> 3. https://github.com/michaelrolnik/qemu-avr/blob/avr-v32/target/avr/gdbstub.c#L66-L68
>>>>
>>>> >
>>>> > A.
>>>> >
>>>> >>
>>>> >> >
>>>> >> > A.
>>>> >> >
>>>> >> >
>>>> >> >
>>>> >> >>
>>>> >> >> +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;
>>>> >> >> +};
>>>> >> >> +
>>>> >> >> +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)
>>>> >> >>
>>>> >>
>>>> >>
>>>> >> --
>>>> >> Best Regards,
>>>> >> Michael Rolnik
>>>>
>>>>
>>>>
>>>> --
>>>> Best Regards,
>>>> Michael Rolnik
>>
>>
>>
>> --
>> Best Regards,
>> Michael Rolnik



--
Best Regards,
Michael Rolnik