Re: [Qemu-devel] [PATCH] target-arm: add dump-guest-memory support

[Peter Maydell]

On 24 December 2014 at 16:54, Rabin Vincent <address@hidden> wrote:
> On Tue, Dec 23, 2014 at 11:45:00PM +0000, Peter Maydell wrote:
>> Assuming the answer is "still 64 bit core dump" you need
>> to do something here to sync the 32 bit TCG state into the
>> 64 bit xregs array. (KVM can take care of itself.)
>
> I have now tested this by triggering a dump while a 32-bit process is
> incrementing a register in a tight loop, and the following, which I
> lifted off the exception handling code, appears to work:
>
>     if (!is_a64(&cpu->env)) {
>         int i;
>
>         for (i = 0; i < 15; i++) {
>             prstatus.regs[i] = cpu->env.regs[i];
>         }
>     }

Yes, that looks OK, but can you factor it out to a function
in target-arm/, please? When we add support for 32-bit EL1
in 64-bit EL2/EL3 it'll need to get more complicated.

Also you need to use the read_cpsr() value for pstate.

>> Note that in fact ARM is never going to be TARGET_WORDS_BIGENDIAN,
>> even if the guest is big-endian, because the #define represents
>> the bus endianness, not whether the CPU happens to currently be
>> doing byte-swizzling. Do you need to key d_endian off the CPU's
>> current endianness setting? The current endianness of EL1?
>> Something else?
>
> IIUC we don't currently support anything other than little endian in
> system emulation?  Attempting to boot a BE ARMv7 vexpress kernel hits
> the unimplementation of setend pretty quickly, and I don't see any
> machine initializing the bswap_code to big endian.

We don't currently in emulation; there are patches on-list to
support it for KVM, though, which I expect we'll be merging
shortly.

(I really should resurrect that patchseries Paolo sent out to
add BE support, it was pretty close but I think needed a few
more tweaks.)

> According the the ELF specification for ARM, the choice between
> ELFDATA2LSB and ELFDATA2MSB "will be governed by the default data order
> in the execution environment".  Since we dump the full system memory I
> would interpret this to be the "lowest" execution environment.  So I
> guess for ARM this would mean setting big endian if (SCTLR.EE ||
> SCTLR.B) and for AArch64 if SCTLR_EL1.E0E is set?

I think AArch64 should be SCTLR_EL1.EE, shouldn't it?

What are the semantics of the dump if we support EL2/EL3?
Do we still just dump from the perspective of EL1? That's
probably the best approximation to useful for a user I guess.

-- PMM