Re: [Qemu-devel] [PATCH v4 2/3] utils: Add helper to read arm MIDR_EL1 register

[Vijay Kilari <vijay.kilari@gmail.com>]

On Fri, Oct 28, 2016 at 2:33 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 28 October 2016 at 08:00, Vijay Kilari <vijay.kilari@gmail.com> wrote:
>> On Thu, Oct 27, 2016 at 9:33 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
>>> On 25 October 2016 at 13:12,  <vijay.kilari@gmail.com> wrote:
>>>> From: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
>>>>
>>>> Add helper API to read MIDR_EL1 registers to fetch
>>>> cpu identification information. This helps in
>>>> adding errata's and architecture specific features.
>>>>
>>>> This is implemented only for arm architecture.
>>>>
>>>> Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
>
>>>> diff --git a/util/Makefile.objs b/util/Makefile.objs
>>>> index 36c7dcc..d14a455 100644
>>>> --- a/util/Makefile.objs
>>>> +++ b/util/Makefile.objs
>>>> @@ -37,3 +37,4 @@ util-obj-y += log.o
>>>>  util-obj-y += qdist.o
>>>>  util-obj-y += qht.o
>>>>  util-obj-y += range.o
>>>> +util-obj-y += aarch64-cpuid.o
>
>>>
>>>> +#include "qemu/cutils.h"
>>>> +#include "qemu/aarch64-cpuid.h"
>>>> +
>>>> +#if defined(__aarch64__)
>>>> +static uint64_t qemu_read_aarch64_midr_el1(void)
>>>> +{
>>>> +#ifdef CONFIG_LINUX
>>>
>>> When will CONFIG_LINUX not be defined but __aarch64__ is?
>>   The contents of this file is compiled only for aarch64
>
> Your makefile change compiles it for everything.
>
>> and hence
>> all the contents are under this __aarch64__.
>> Also the code is only for linux, have added CONFIG_LINUX.
>
> ...and you haven't answered the question: in what
> circumstances could __aarch64__ be defined but
> CONFIG_LINUX is not, ie why is there any point in
> checking both defines?

Ok. You mean __aarch64__ and __linux__ both are defined by gcc.
we can rely on __aarch64__ define  here?.

AFAIK, the caller of this function bufferiszero.c is compiled
for everything, I case of bufferiszero.c is compiled for other than
linux for aarch64, compilation might fail. In such case, the header file
needs to have dummy/empty functions.