Re: [Qemu-devel] arm1136 CPU emulation won't run current kernels?

[Peter Maydell]

On 8 June 2011 01:32, Rob Landley <address@hidden> wrote:
> QEMU's -cpu arm1136 emulation stopped working in the 2.6.35 and later
> kernels, now QEMU dies early in the kernel boot with:
>
>  qemu: fatal: Unimplemented cp15 register write (c13, c0, {0, 3})

> The CPUID for arm1136 QEMU emulates a process that should have hardware
> TLS (target-arm/cpu.h):
>
> #define ARM_CPUID_ARM1136     0x4117b363
>
> Meaning the above "switch it off" test doesn't trigger, the kernel tries
> to access a hardware feature QEMU doesn't emulate, and QEMU aborts.
>
> Note: I can work around this with -cpu arm1136-r2 (0x4107b363),

The QEMU bug here is that we provide the TLS cp15 registers only
if ARM_FEATURE_V6K, which is almost right except that they are also
available on the ARM1136 r1p0 and above. (I note in passing that the
QEMU CPU name "arm1136-r2" is rather misleading because in fact it's
providing an r0p2. The only difference to "arm1136" in the QEMU model
currently is the CPUID register value.)

1136r1p0 and above are a kind of halfway-house between v6 and v6K:
they have TLS regs, CLREX, load-store-exclusive for non-word sizes
and the NOP instruction, but are missing the v6K VA-PA translation,
SEV, WFE, WFI and YIELD.

I guess we need some more finegrained feature switches here
(also I think some actual code which implements "V7 implies
V6K, V6, V5, V4T" and so on rather than having each CPU set
them all by hand).

> (Is there a data sheet somewhere...?)

CPU-specific manuals (TRMs) are available from http://infocenter.arm.com/
The architecture reference manual is also available if you register as
a user on the website, which I'm told is a fairly hassle-free process.

-- PMM