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

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpxchg helpers
Date: Thu, 6 Apr 2017 08:53:55 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

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.


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