Re: access guest address from within instruction

[BitFriends <commandspider12@gmail.com>]

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my bad, then I was mislead by "Which is, in general, what you want for
implementing a custom instruction". Also the code around me is full of gen
instructions, so I thought that's what I should use.

So, when reading the doc I found out about the cpu_{ld,st}*_mmu functions.
That sounds more what I want for a direct action, No?

Regards

BitFriends

Richard Henderson <richard.henderson@linaro.org> schrieb am So., 2. Okt.
2022, 16:40:

> On 10/2/22 02:20, BitFriends wrote:
> > I now came up with this code:
> >
> > TCGv_i64 res = 0;
> > TCGv_i64 addr = (TCGv_i64)(env->regs[R_EDI]);
> >
> > tcg_gen_qemu_ld_i64(res, addr, 0, MO_LEUQ);
> >
> > env->regs[R_EAX] = (target_ulong)res;
> >
> > However this crashes afterwards in test_bit. Maybe this is caused by an
> invalid access?
> > Anything wrong about the code? This still gives some warnings, like
> TCGv_i32 expected (and
> > when you use TCGv_i32, it says TCGv_i64 expected) plus some casting
> warnings.
>
> It is as if you did not read the second paragraph of my response at all.
> tcg_gen_qemu_ld_i64 is for generating code, not performing a direct action.
> Can you see how your code differs from *all* of the code around it?
>
> r~
>
> >
> > Am Sa., 1. Okt. 2022 um 22:23 Uhr schrieb Richard Henderson <
> richard.henderson@linaro.org
> > <mailto:richard.henderson@linaro.org>>:
> >
> >     On 10/1/22 13:10, BitFriends wrote:
> >      > Hello,
> >      >
> >      > I am trying to create a custom instruction that accesses guest
> memory specified by an
> >      > address in a register. I specifically want to read from that
> address. So I tried to do
> >      > that using "tcg_gen_qemu_ld_i64(&res, env->regs[R_EDI], 0,
> MO_LEUQ);", but that
> >     doesn't
> >      > save any result in res.
> >
> >     This statement should have given you compilation errors, so I don't
> know what you mean by
> >     "doesn't save any result".  There's clearly a disconnect between
> what you describe and
> >     what you actually attempted.
> >
> >     Anyway, by the name you can see that function "gen"erates a "tcg"
> operation, which is
> >     then
> >     later compiled by the jit, the output of which is later executed to
> produce a result.
> >     Which is, in general, what you want for implementing a custom
> instruction.
> >
> >
> >     r~
> >
>
>

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