[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH 2/2] s390x: Add laa and laag instructions

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 2/2] s390x: Add laa and laag instructions
Date: Tue, 12 May 2015 21:22:05 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/12/2015 05:53 AM, Richard Henderson wrote:
On 05/07/2015 06:12 PM, Alexander Graf wrote:
+static ExitStatus op_laa(DisasContext *s, DisasOps *o)
+    TCGv_i64 m2 = tcg_temp_new_i64();
+    /* XXX should be atomic */
+    tcg_gen_qemu_ld32s(m2, o->in2, get_mem_index(s));
+    /* Set r1 to the unmodified contents of m2 */
+    tcg_gen_mov_i64(o->out, m2);
+    /* m2 = r3 + m2 */
+    tcg_gen_add_i64(m2, o->in1, m2);
+    tcg_gen_qemu_st32(m2, o->in2, get_mem_index(s));
+    /* Set in2 to the input operand for cc calculation */
+    tcg_gen_mov_i64(o->in2, o->out);
+    tcg_temp_free_i64(m2);
+    return NO_EXIT;
I don't believe that this computes the right cc.
You need to place m2 into in2, not out.

That said, maybe

   o->in2 = m2;

is the right way to perform that copy.  Since we
know that in2 was in2_a2, allocating a temp for an
address, we also know we can both (1) free it and
(2) put another temp in there that will be freed.

Well, alternatively I could try to make out be the memory value at the end of the op and invent new load/store helpers for atomic instructions. That way the op bit should shrink significantly and we get the correct operand in s->out automatically.

Don't worry about the atomic-ness of the operation
until some of the many patch sets going round on
that very subject are resolved.  This will be good
enough for system mode for now.

I think maybe the whole target ought to be cleaned
up for the new TCGMemOps.  For this, you could share
the code for LAA and LAAG with the TCGMemOp in insn->data.

That's an interesting idea. Let me see what I can pull off.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]