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

From: Nikunj A Dadhania
Subject: Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpxchg helpers
Date: Fri, 07 Apr 2017 10:44:03 +0530
User-agent: Notmuch/0.23.5 (https://notmuchmail.org) Emacs/25.1.1 (x86_64-redhat-linux-gnu)

Richard Henderson <address@hidden> writes:

> 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.

Sure, here you are mentioning cpu_so being moved to CRF.


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