![]() a 32-bit ARM machine performing the same arithmetic, we can write C programs that will give different results on different CPUs) Math behaves the same (consider a 64-bit x86 machine performing 64-bit arithmetic vs.Memory alignment will match reality (x86 supports unaligned memory access, ARMv5 does not and we can write C code that will not work on ARMv5).There’s arguably value in running unit tests on their target CPU (even if that CPU is emulated), for example: Furthermore, the unit test executables themselves never need to leave my build system (that is, they don’t need to wind up on the target root file system or even an emulated device) and I do not need a special build just for running those tests. ![]() In addition, $? will report the cross-compiled program’s return code correctly so with the help of the target ELF interpreter and libraries I can now run unit tests after building my BSP, those unit tests can run in their native architecture, and I can capture output from them and utilize their return codes (for example via make check in autotools) like I would expect with native unit tests. Target/bin/busybox: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 4.7.0, not strippedĪnd target/ has lib/ld-linux.so.3 present so passing -L target gets me a running executable. I can take advantage of the fact that target/ has everything that is needed to run an executable (that is, there’s a /lib directory there with libraries in the target architecture) so now I can use qemu to run an executable. I have built a BSP using buildroot and now have a target/ directory that contains nearly everything that will wind up on my root file system image (but note a few caveats) for this target. Additional environment variables can be set with -E. The -L option lets us specify the path for the ELF interpreter prefix and we can utilize this to point the emulator to a reasonable set of libraries (for example a target file system sitting on my x86 laptop). ![]() qemu user mode takes a number of arguments that can be used to supply these. There is also a user mode which lets us run a cross-compiled executable right on our host machine and that can be used for various isolated testing tasks (for instance, running unit tests in the target system architecture).Ī useful program does need some libraries however and it may need an environment. We can use qemu-system-arm to start a simulated ARM-based machine, boot Linux, and then run whatever software is appropriate. This can make QEMU difficult to use at first, but this provides flexibility in creating exactly the virtual machine that you want.The qemu CPU emulator is typically used to emulate an entire system, for example QEMU uses command line options to define everything. ![]() Unlike PC emulator systems like VMware or VirtualBox, you need to "build" your virtual system by instructing QEMU to add each component of the virtual machine. $ qemu-img create image.img 200M Run QEMU To create an image file that's about 200MB, type this: To initialize a file that you can use as a virtual C: drive, use the qemu-img command. Under QEMU, virtual drives are image files. Other media, including other hard drives or CD-ROM drives, are assigned D:, E:, and so on. A: and B: are the first and second floppy disk drives, and C: is the first hard drive. In DOS, just as in Windows, drives are represented as letters. You'll need a place to install the legacy system inside QEMU, and for that you'll need a virtual C: drive.
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