Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpxchg helpers

[Richard Henderson]

On 04/06/2017 03:22 AM, Nikunj A Dadhania wrote:
>      tcg_gen_trunc_tl_i32(cpu_crf[0], cpu_so);
>      l1 = gen_new_label();
>      tcg_gen_brcond_tl(TCG_COND_NE, EA, cpu_reserve, l1);
> -    tcg_gen_ori_i32(cpu_crf[0], cpu_crf[0], CRF_EQ);
> -    tcg_gen_qemu_st_tl(cpu_gpr[reg], EA, ctx->mem_idx, memop);
> +
> +    t0 = tcg_temp_new();
> +    tcg_gen_atomic_cmpxchg_tl(t0, EA, cpu_reserve_val, cpu_gpr[reg],
> +                              ctx->mem_idx, DEF_MEMOP(memop));

Actually, I noticed another, existing, problem.

This code changes CRF[0] before the user memory write, which might fault.  This 
needs to delay any changes to the architecture visible state until after any 
exception may be triggered.


r~