Dhrystone2i.apk does not run ARMv8 benchmark - benchmarking

I installed Dhrystone2i.apk from http://www.roylongbottom.org.uk/android%2064%20bit%20benchmarks.htm . The website claims it will run 64-bit when supported. I installed on a board which has 4x Cortex-A53 running Android 6.0. It only runs ARMv7 32-bit Dhrystone. What needs to happen to make the benchmark run the ARMv8 64-bit Dhrystone?

Linux kernel is 32 bit, the same as my new (now Lenovo) Moto 4G phone with Cortex-A53. I also have a Lenovo Tab 2, with Cortex-A53, that runs 64 bit benchmarks. On system details provided by the benchmark, the only difference is that the latter CPU and architecture are identified as AArch64, compared ARMv7 or 7. The tablet also indicates AArch64 when running 32 bit only benchmarks. The Linux version code does not appear to identify 32 or 64 bits.


How to start a virtual machine guest armv8 on amd64 host with qemu

How to run a virtual machine with qemu on an Ubuntu 18.04 x86_64 host system, when I want the guest system to be ARMv8 (Raspberry Pi 3, more specifically interested in the Cortex A53 processor)?
I want to compile a project for a real machine with ARMv8 on the mentioned host system. Currently, this is done with cross compile directly in the host system. For many different reasons, I want to set up a virtual machine which compiles binaries (virtually) native for the ARMv8. The binaries need to be runable on the real ARMv8 machine later.
Apart from Qemu and the right qemu-system-aarch64 to be installed on the host system, there is an image of the operating system needed. Ideally the same as the one running on the real ARMv8 device. The Ubuntu IoT Core 18.04 64-bit is available at https://ubuntu.com/download/raspberry-pi and I saved it to a local folder with the name ubuntu18045arm64rpi3.img.xz.
After extracting it, I got the extracted image 'ubuntu18045arm64rpi3.img'
To start a virtual machine with the given image and the wanted architecture, I type this:
sudo qemu-system-aarch64 -m 1024 -cpu cortex-a53 -M virt -drive if=none,file=ubuntu18045arm64rpi3.img,id=hd0
which gives me a window like that:
Now my main questions are:
I expected a virtual machine to boot up, where I can install the OS from the given image. What did I do wrong or how to achieve this goal?
Later on, I want to install a compiler (if not already there) on the guest ARMv8 machine and compile my project there. Afterwards I plan to transfer the compiled binaries to the real ARMv8 machine and expect them to run without difficulties. Is this possible with the current approach?
You can't just pass a disk image to the aarch64 QEMU and have it boot. You need to either pass a kernel to boot, or a BIOS (probably UEFI) image (which can then read a kernel off a disk image).
This blog post has an example of running Debian on QEMU; getting Ubuntu booting is probably similar.
Your link is to a raspberry pi specific disk image -- since you are not asking QEMU to model a raspberry pi board I would recommend against using that. You want whatever Ubuntu provides as their most normal/generic aarch64 image. If you're going the "boot via UEFI" route then you want a disk image intended for SBSA/UEFI systems.
On your second question about portability of compiled binaries, this is the same as for any two Linux systems, really. If the two systems have the same OS/distro version (so they have the same library versions etc), and the same sets of runtime libraries installed, and you didn't tell the compiler to compile to use CPU features that the destination CPU doesn't have, then it should work.
Compiling inside this emulated setup is going to be significantly slower than either your current cross-compile setup or compiling the binaries directly on the real AArch64 hardware, incidentally.

ARMv8 backward compatibility with ARMv7 (Snapdragon 820 vs Cortex-A15)

I see that ARMv8 is merely an extension of ARMv7 architecture and all code compiled on ARMv7 should run on ARMv8. I am interested in the backward compatibility of ARMv8 to ARMv7. Will code that was compiled on ARMv8 run on ARMv7?
I have a particular exact case of interest: I would like to run the comma.ai's Openpilot visiond binary which was compiled for the OnePlus 3 smartphone (Qualcomm MSM8996 Snapdragon 820 CPU) on the Nvidia Jetson TK1 (NVIDIA Cortex-A15 CPU). Will the visiond run on Jetson?
EDIT: There may be more in question than CPU compatibility since visiond probably heavily uses GPU on that phone. Will probably depend whether they use some standard parallelization ways (OpenCL, NEON etc.) or have some custom code for Snapdragons GPU. Even with OpenCL the chance of compatibility is probably quite low on different HW.
I believe that aarch32 userland is fully or very highly backwards compatible with ARMv7, i.e. userland programs compiled for ARMv7 should just work in AArch32, but I couldn't find a precise quote in the ARM manual.
aarch32 does have new instructions added over ARMv7 however, most of them seem to be functionality that ARMv8 added and the designers decided to expose on aarch32. Therefore, aarch32 is not forward compatible with ARMv7, i.e., programs compiled for aarch32 might not run on ARMv7.
I'm not sure about system land. See also: Does ARMv8 AArch32 mode has backward compatible with armv4 , armv5 or armv6?

AMD64 run on i586 or vice-versa?

I have a small C program that I wish to port from Linux to Windows. I can do this with the MinGW compiler, and I have noticed that it has two different prefixes, amd64 and i586. I am on an i686 computer and I was wondering if I compile my C program using and amd64 architecture, will it run on my i686 machine? And vice-versa?
Is there a compiler that compile C code to run on ANY architecture?
If you compile your code for i586 (actually what is commonly called x86) it should work fine on AMD64 (x86-64) processors, since x86-64 processors can execute "legacy" 32 bit code, as long as the OS supports this - and mainstream OSes usually do; Windows support for 32 bit applications in particular is really good, since most applications installed on the average Windows system are still 32 bit.
The contrary instead does not hold true, since the x86-64 instruction set is (loosely speaking) an expansion of the x86 architecture, so any non-64 bit x86 processor wouldn't know how to interpret the new machine code (and even if it knew it, it wouldn't have the resources to run it).
As for the edit, you can't generate machine code that runs natively everywhere; the usual solution in such cases is to use pseudo-compiled languages that output an intermediate-level machine code that needs an architecture-specific VM installed to be run (the classic example here is Java and .NET). If instead you use a language compiled to "native code", you have to generate an executable for each target platform.

I am developing a 64 bit application. Is it possible to run the 64 bit application on a 32 bit OS?

I am developing a 64 bit application. Is it possible to run the 64 bit application on a 32 bit OS?
Please note that the question is generic and not specific to Windows OS. Infact the application in itself is portable across OS.
(We'll assuming your talking about AMD64 (== EM64T == x86_64) and x86 for 64-bit and 32-bit respectively)
You can run AMD64 code on x86 processors only by emulation (e.g. qemu), or some kinds of virtualisation (I believe VMWare might support 64bit guest OS on 32bit host OS on 64
bit capable CPU). However this means running a 64-bit OS as a guest on emulation or virtualisation I believe.
As you're developing the application, it shouldn't be too hard to develop both 32-bit and 64-bit builds of your code.
For Mac you can ship a single binary that has both types of code in it, or Mac OSX can run your 64-bit binary on a 32-bit kernel (only on a x86_64 capable processor though). For Windows and Linux, you'll either have to ship separate installers, or ship some smart installer, that selects the correct binaries at install time. For Linux there is a project for add the ability to run AMD64 code on x86 kernel on AMD64 processor - http://linuxpae64.sourceforge.net/ - but it doesn't look like it's got very far into the mainline kernel.
Is there a particular reason you only want to produce 64-bit binaries?
If it's to access extra memory, then the 32-bit OS wouldn't be able to give you extra memory anyway.
If it's to avoid have to test 2 different versions, then just produce the 32-bit version, it'll work on Windows AMD64, and most Linux AMD64 distributions without problems.
On windows, only using a virtual machine.
On OS X, 64Bit apps run natively (thanks Stephen)
The other way around is fine, bit I dont think you can run a 64bit app on a 32bit OS, you may be able to using a virtual machine or some kind of virtualisation.
There's an easier solution than trying to run a 64-bit program on a 32-bit OS (including executing through an emulated or virtual 64-bit platform on top of the 32-bit OS): recompile it for the 32-bit OS.
When you said it's portable across different OSes, did you also mean non-64-bit OSes? I could not call something portable without qualifying "only 64-bit" if that was the case, and I think many (maybe even most?) programmers also expect that qualification, at least currently.
it is possible using qemu in soft emulation mode
See Microsoft FAQ:
The terms 32-bit and 64-bit refer to
the way a computer's processor (also
called a CPU), handles information.
The 64-bit version of Windows handles
large amounts of random access memory
(RAM) more effectively than a 32-bit
system. For more details, go to A
description of the differences between
32-bit versions of Windows Vista and
64-bit versions of Windows Vista
Understand the difference between 32-bit and 64-bit and you will see why it's not possible.
See this (assuming you're running Windows):
If the program is specifically designed for the 64-bit version of Windows, it won't work on the 32-bit version of Windows. (However, most programs designed for the 32-bit version of Windows will work on the 64-bit version of Windows.)
Device drivers designed for the 64-bit version of Windows won't work on computers running a 32-bit version of Windows. To learn how to check for drivers, see Update a driver for hardware that isn't working properly or go to the device manufacturer's website.
On Windows, no. On OS X, yes. I don't know what the state of affairs is on Linux.
In fact, Snow Leopard boots into a 32-bit kernel, but compiles applications 64-bit by default, so this is quite common on OS X.
A 64 bit application does not run on a 32 bit processor period
A 64 bit application uses a 64 bit wide register. It just plain won't fit.

Flash ocx "Class not registered" on Windows 7 x64

I have a WPF app that uses Flash10c.ocx developed on a 32 bit machine. I didn't have to register the ocx on my dev machine, I just installed the latest flash, added a reference and started coding. When testing on a 64 bit system I get ye old "Class not registered" which I think mean I need to regsvr the ocx. Is it Ok to just copy the 32 bit ocx (I'm pretty sure its 32 bit as its located in C:\Windows\System32\Macromed on the dev system) to a 64 bit system and register it?
Update: regsvr32 /i flash10c.ocx errors out with "The module flash10c.ocx las loaded but the call to DllRegisterServer failed with error code 0x80004005"
Update 2: I've given up on this and decided to run Flash on 32 bit systems only. If anyone has a better answer I'd like to hear it but I'm marking the current suggestion as answered to give due credit for the effort.
The reason it's not working for you is that your WPF application is running as 64-bit.
A .NET application is able to run as 32-bit or 64-bit; and the CLR is JITing your app to whatever architecture the application is running on - in this case 64-bit.
Except you now want your 64-bit application to load a 32-bit dll. This is not possible. A 64-bit process can only load 64-bit dlls. A 32-bit process can only load 32-bit dlls. No amount of fiddling with COM object registration will change this; it's not a question of missing registry entries.
Adobe Flash only comes as a 32-bit dll. Adobe does not now (and hopefully will never) have a 64-bit version.
In order for your WPF .NET application to load the 32-bit flash dll, it needs to be running as 32-bit process. There is a way, in Visual Studio's build configuration, to force your .NET application to only target x86, rather than Any CPU.
The choices of CPU targets are:
Flash, for what it's worth, doesn't have an Itanium version, either.
See StackOverflow: Visual Studio “Any CPU” target for more discussion about target cpus.
May be the flash installer is meant to be only for 32 bit OS. Hence it did not install properly on a 64 bit machine. The error means that you will need to manually register the ocx but will it register successfully that's a totally different question.
Edit 1: here is Adobe's statement of support for 64-bit systems (there is none) (I assume you are using 64 bit browser on a 64 bit machine)
Edit 2: Another forum message about Flash on 64-bit Windows.