Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand

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Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand

From:	Richard Henderson
Subject:	Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand
Date:	Sun, 17 Oct 2021 23:05:16 -0700
User-agent:	Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0

On 10/17/21 10:38 PM, Alistair Francis wrote:

Do we get much of an advantage from this though? To me it seems
confusing that the mstatus register doesn't actually contain the
latest value (for example when debugging QEMU and adding my own
printf's).

(1) We have at least 3 places that need to check the cpu state in order to set SDcorrectly; we would add another couple with the VS bit that's coming in from RVV-1.0. Bysetting this bit during read, we reduce that to one accessor for read.

(2) We would need to move this bit when changing MXL, once that's possible with thevarious XLEN changing patch sets.

(3) The position of this bit, between MSTATUS and SSTATUS, differs if MXL != SXL, whichmeans that there is not really one correct setting for (2).

r~

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[PATCH v3 08/14] target/riscv: Replace is_32bit with get_xl/get_xlen, (continued)
- [PATCH v3 08/14] target/riscv: Replace is_32bit with get_xl/get_xlen, Richard Henderson, 2021/10/16
- [PATCH v3 11/14] target/riscv: Adjust trans_rev8_32 for riscv64, Richard Henderson, 2021/10/16
- [PATCH v3 10/14] target/riscv: Use gen_arith_per_ol for RVM, Richard Henderson, 2021/10/16
  - Re: [PATCH v3 10/14] target/riscv: Use gen_arith_per_ol for RVM, Alistair Francis, 2021/10/18
- [PATCH v3 09/14] target/riscv: Replace DisasContext.w with DisasContext.ol, Richard Henderson, 2021/10/16
- [PATCH v3 06/14] target/riscv: Use REQUIRE_64BIT in amo_check64, Richard Henderson, 2021/10/16
- [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand, Richard Henderson, 2021/10/16
  - Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand, Alistair Francis, 2021/10/18
    - Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand, Richard Henderson, 2021/10/18
    - Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand, Alistair Francis, 2021/10/18
    - Re: [PATCH v3 14/14] target/riscv: Compute mstatus.sd on demand, Richard Henderson <=
- [PATCH v3 12/14] target/riscv: Use gen_unary_per_ol for RVB, Richard Henderson, 2021/10/16
  - Re: [PATCH v3 12/14] target/riscv: Use gen_unary_per_ol for RVB, Alistair Francis, 2021/10/18
- [PATCH v3 13/14] target/riscv: Use gen_shift*_per_ol for RVB, RVI, Richard Henderson, 2021/10/16
  - Re: [PATCH v3 13/14] target/riscv: Use gen_shift*_per_ol for RVB, RVI, Alistair Francis, 2021/10/18

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