ARM: RES0/RES1 SCTLR fields not read-only

[Yifan]

There are fields in SCTLR that are RAO/SBOP or WI or in the case of the RR field, accessible only in secure mode. Currently it seems that qemu just propagates any write to SCTLR to the register and this screwed up in a bootloader that I am debugging.

[Peter Maydell (pmaydell)]

On 3 April 2017 at 23:17, Yifan <email address hidden> wrote:
> There are fields in SCTLR that are RAO/SBOP or WI or in the case of the
> RR field, accessible only in secure mode. Currently it seems that qemu
> just propagates any write to SCTLR to the register and this screwed up
> in a bootloader that I am debugging.

Yes, we're a bit loose in QEMU on the handling of reserved bits.

Note that most of the SCTLR bits like this are RAO/SBOP or RAZ/SBZP,
so the guest should not be writing wrong values to them.

thanks
-- PMM

[Yifan (yifanlu)]

So there won't be a fix in the future? I'm working with debugging a proprietary bootloader that I do not have the source code for. I wonder if this becomes an issue for any other platform targets.

[Peter Maydell (pmaydell)]

Well, I wouldn't object to a patch to fix it (it would have to correctly handle the various different versions of the CPU architecture we implement, etc), but I'm not planning on writing one today myself.

[Thomas Huth (th-huth)]

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