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Re: [Qemu-devel] [PATCH] target-tilegx: Execute _start and reach to __li

From: Chris Metcalf
Subject: Re: [Qemu-devel] [PATCH] target-tilegx: Execute _start and reach to __libc_start_main successfully
Date: Thu, 26 Feb 2015 22:01:48 -0500
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 2/25/2015 8:44 PM, Chen Gang S wrote:
On 02/26/2015 01:19 AM, Richard Henderson wrote:
On 02/24/2015 05:40 PM, Chen Gang S wrote:
+static int gen_shl16insli(struct DisasContext *dc,
+                          unsigned char rdst, unsigned char rsrc, short im16)
Use uint16_t, as the field is not signed.

objdump print it as signed, e.g. "shl16insli r32, r32, -30680"
I think you've just found a bug in objdump.  ;-)

According to the ISA document, I guess, it assumes imm16 is unsigned
number (although ISA document does not mention about it, directly). But
for tcg_gen_ori_i64, it assumes imm16 is signed number:

   void tcg_gen_ori_i64(TCGv_i64 ret, TCGv_i64 arg1, int64_t arg2);

So for me, I am not sure that objdump must be a bug. For safety reason,
I still prefer to treat imm16 as signed number.

You have to consider the immediate value as having the high 48 bits zero
when you "or" it into the result, so it's hard to consider it as signed in
any meaningful way.  Richard is right.

Y1 can issue branches, which can be buffered. And Y1 also can issue call
(which will store pc to sp stack) -- e.g. jalr, jalrp.

Richard already covered this, but yes, jal/jalr etc are not memory ops.
There is only one memory op possible per bundle.

Chris Metcalf, EZChip Semiconductor

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