Re: [PATCH 1/2] target/riscv: Add scontext CSR handling

[Daniel Henrique Barboza <dbarboza@ventanamicro.com>]

On 2/26/25 11:39 AM, Florian Lugou wrote:
> scontext size is 16 bits on RV32 and 32 bits on RV64, as recommended by
> version 1.0 2025-02-21 of the debug specification.
> 
> When the Smstateen extension is implemented, accessibility to the
> scontext CSR is controlled by bit 57 of the [mh]stateen0 CSRs.
> 
> Signed-off-by: Florian Lugou <florian.lugou@provenrun.com>
> ---

Can you please rebase these patches on top of the maintainer's tree:

https://github.com/alistair23/qemu/tree/riscv-to-apply.next

This patch will have a conflict on cpu_bits.h in that tree.


Looks good otherwise. Thanks,

Daniel


>   target/riscv/cpu.h      |  1 +
>   target/riscv/cpu_bits.h |  5 +++++
>   target/riscv/csr.c      | 36 ++++++++++++++++++++++++++++++++++++
>   target/riscv/debug.c    |  1 +
>   4 files changed, 43 insertions(+)
> 
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 97713681cb..e47200f409 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -430,6 +430,7 @@ struct CPUArchState {
>       target_ulong tdata2[RV_MAX_TRIGGERS];
>       target_ulong tdata3[RV_MAX_TRIGGERS];
>       target_ulong mcontext;
> +    target_ulong scontext;
>       struct CPUBreakpoint *cpu_breakpoint[RV_MAX_TRIGGERS];
>       struct CPUWatchpoint *cpu_watchpoint[RV_MAX_TRIGGERS];
>       QEMUTimer *itrigger_timer[RV_MAX_TRIGGERS];
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index f97c48a394..add0bb9d0e 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -247,6 +247,9 @@
>   #define CSR_SIEH            0x114
>   #define CSR_SIPH            0x154
>   
> +/* Supervisor-Level Sdtrig CSRs (debug) */
> +#define CSR_SCONTEXT        0x5a8
> +
>   /* Hpervisor CSRs */
>   #define CSR_HSTATUS         0x600
>   #define CSR_HEDELEG         0x602
> @@ -959,4 +962,6 @@ typedef enum RISCVException {
>   #define MCONTEXT64                         0x0000000000001FFFULL
>   #define MCONTEXT32_HCONTEXT                0x0000007F
>   #define MCONTEXT64_HCONTEXT                0x0000000000003FFFULL
> +#define SCONTEXT32                         0x0000FFFF
> +#define SCONTEXT64                         0x00000000FFFFFFFFULL
>   #endif
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index afb7544f07..1c1ac8ed67 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -3221,6 +3221,10 @@ static RISCVException write_mstateen0(CPURISCVState *env, int csrno,
>           wr_mask |= SMSTATEEN0_P1P13;
>       }
>   
> +    if (riscv_cpu_cfg(env)->debug) {
> +        wr_mask |= SMSTATEEN0_HSCONTXT;
> +    }
> +
>       if (riscv_cpu_cfg(env)->ext_smaia || riscv_cpu_cfg(env)->ext_smcsrind) {
>           wr_mask |= SMSTATEEN0_SVSLCT;
>       }
> @@ -5053,6 +5057,35 @@ static RISCVException write_mcontext(CPURISCVState *env, int csrno,
>       return RISCV_EXCP_NONE;
>   }
>   
> +static RISCVException read_scontext(CPURISCVState *env, int csrno,
> +                                    target_ulong *val)
> +{
> +    RISCVException ret = smstateen_acc_ok(env, 0, SMSTATEEN0_HSCONTXT);
> +    if (ret != RISCV_EXCP_NONE) {
> +        return ret;
> +    }
> +
> +    *val = env->scontext;
> +    return RISCV_EXCP_NONE;
> +}
> +
> +static RISCVException write_scontext(CPURISCVState *env, int csrno,
> +                                     target_ulong val)
> +{
> +    bool rv32 = riscv_cpu_mxl(env) == MXL_RV32 ? true : false;
> +
> +    RISCVException ret = smstateen_acc_ok(env, 0, SMSTATEEN0_HSCONTXT);
> +    if (ret != RISCV_EXCP_NONE) {
> +        return ret;
> +    }
> +
> +    /* Spec suggest 16-bit for RV32 and 34-bit for RV64 */
> +    target_ulong mask = rv32 ? SCONTEXT32 : SCONTEXT64;
> +
> +    env->scontext = val & mask;
> +    return RISCV_EXCP_NONE;
> +}
> +
>   static RISCVException read_mnscratch(CPURISCVState *env, int csrno,
>                                        target_ulong *val)
>   {
> @@ -5705,6 +5738,9 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
>       [CSR_SIEH]       = { "sieh",   aia_smode32, NULL, NULL, rmw_sieh },
>       [CSR_SIPH]       = { "siph",   aia_smode32, NULL, NULL, rmw_siph },
>   
> +    /* Supervisor-Level Sdtrig CSRs (debug) */
> +    [CSR_SCONTEXT]   = { "scontext", debug, read_scontext, write_scontext },
> +
>       [CSR_HSTATUS]     = { "hstatus",     hmode,   read_hstatus, write_hstatus,
>                             .min_priv_ver = PRIV_VERSION_1_12_0                },
>       [CSR_HEDELEG]     = { "hedeleg",     hmode,   read_hedeleg, write_hedeleg,
> diff --git a/target/riscv/debug.c b/target/riscv/debug.c
> index f6241a80be..914a9ce0f8 100644
> --- a/target/riscv/debug.c
> +++ b/target/riscv/debug.c
> @@ -1086,4 +1086,5 @@ void riscv_trigger_reset_hold(CPURISCVState *env)
>       }
>   
>       env->mcontext = 0;
> +    env->scontext = 0;
>   }