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Re: [PATCH 06/10] target/arm: Implement v8.1M branch-future insns (as NO
Re: [PATCH 06/10] target/arm: Implement v8.1M branch-future insns (as NOPs)
Tue, 13 Oct 2020 09:58:29 -0700
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On 10/12/20 8:37 AM, Peter Maydell wrote:
> v8.1M implements a new 'branch future' feature, which is a
> set of instructions that request the CPU to perform a branch
> "in the future", when it reaches a particular execution address.
> In hardware, the expected implementation is that the information
> about the branch location and destination is cached and then
> acted upon when execution reaches the specified address.
> However the architecture permits an implementation to discard
> this cached information at any point, and so guest code must
> always include a normal branch insn at the branch point as
> a fallback. In particular, an implementation is specifically
> permitted to treat all BF insns as NOPs (which is equivalent
> to discarding the cached information immediately).
> For QEMU, implementing this caching of branch information
> would be complicated and would not improve the speed of
> execution at all, so we make the IMPDEF choice to implement
> all BF insns as NOPs.
> Signed-off-by: Peter Maydell <firstname.lastname@example.org>
Reviewed-by: Richard Henderson <email@example.com>
[PATCH 05/10] target/arm: Don't allow BLX imm for M-profile, Peter Maydell, 2020/10/12
[PATCH 08/10] target/arm: Fix has_vfp/has_neon ID reg squashing for M-profile, Peter Maydell, 2020/10/12
[PATCH 04/10] target/arm: Make the t32 insn[25:23]=111 group non-overlapping, Peter Maydell, 2020/10/12
[PATCH 06/10] target/arm: Implement v8.1M branch-future insns (as NOPs), Peter Maydell, 2020/10/12
- Re: [PATCH 09/10] target/arm: Implement FPSCR.LTPSIZE for M-profile LOB extension, (continued)
[PATCH 10/10] target/arm: Fix writing to FPSCR.FZ16 on M-profile, Peter Maydell, 2020/10/12
- Re: [PATCH 06/10] target/arm: Implement v8.1M branch-future insns (as NOPs),
Richard Henderson <=