[Qemu-devel] What's the difference between "ld/st" and "qemu_ld/st" in TCG IR?

[Qemu-devel] What's the difference between "ld/st" and "qemu_ld/st" in TCG IR?

[浩倫 魏]

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Hi, all:
I've been trying to understand the process of binary translation inside TCG.If I haven't misunderstood, qemu_ld/st are the operations that will call helper function(ld_mmu) to let softmmu translate the GVA->GPA for the guest load/store instructions. 
So there are some points that I hope you can help me out:
1. Is every guest load/store instruction would be translated to qemu_ld/st IR?
2. What about another TCG IR "ld/st"? What kind of guest instructions would cause TCG generates that IRs and for what purpose?
Any reply would be helpful to me.Thanks in advance.

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Re: [Qemu-devel] What's the difference between "ld/st" and "qemu_ld/st" in TCG IR?

[Richard Henderson]

On 05/23/2015 05:26 AM, 浩倫 魏 wrote:
> So there are some points that I hope you can help me out:
> 1. Is every guest load/store instruction would be translated to qemu_ld/st IR?

Yes.

> 2. What about another TCG IR "ld/st"? What kind of guest instructions would
> cause TCG generates that IRs and for what purpose?

For instance, vector instructions are often implemented without TCG 
temporaries, but instead using ld/st to load the data from the ENV pointer 
directly.  You can see that in the ARM and i386 targets.

Otherwise, there are sometimes less-used system values that do not warrent a 
TCG temporary.  You can see that in the alpha target.


r~

Re: [Qemu-devel] What's the difference between "ld/st" and "qemu_ld/st" in TCG IR?

[浩倫 魏]

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Dear Richard:
Now I get it, thanks for the help! :-)
 


     Richard Henderson <rth@twiddle.net> 於 2015/5/24 (週日) 6:21 AM 寫道﹕
   

 On 05/23/2015 05:26 AM, 浩倫 魏 wrote:
> So there are some points that I hope you can help me out:
> 1. Is every guest load/store instruction would be translated to qemu_ld/st IR?

Yes.

> 2. What about another TCG IR "ld/st"? What kind of guest instructions would
> cause TCG generates that IRs and for what purpose?

For instance, vector instructions are often implemented without TCG 
temporaries, but instead using ld/st to load the data from the ENV pointer 
directly.  You can see that in the ARM and i386 targets.

Otherwise, there are sometimes less-used system values that do not warrent a 
TCG temporary.  You can see that in the alpha target.


r~



  

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