Re: [Qemu-devel] [PATCH 3/3] tcg/aarch64: implement new TCG target for aarch64

[Richard Henderson <rth@twiddle.net>]

On 05/14/2013 07:05 AM, Claudio Fontana wrote:
>> Conditional branch range is +-1MB.  You'll never see a TB that large.  You
>> don't need to emit a branch-across-branch.
> 
> Is there maybe a way to do it right even in the corner case where we have
> a huge list of hundreds of thousands of instructions without jumps and then a conditional jump?
> Are we _guaranteed_ to never see that large a TB with some kind of define,
> similarly to MAX_CODE_GEN_BUFFER_SIZE?

There are three mechanisms that all limit TB size:
  (1) OPC_MAX_SIZE, limiting the number of opcodes emitted,
  (2) CF_COUNT_MASK, limiting the number of instructions translated,
  (3) Instruction pointer crossing a page boundary, where we end a TB
      and re-verify the page protection bits of the new page.

Nr 1 is probably the most significant, since it most directly relates to
the number of output instructions, and thus the resulting TB size.


r~