On Wed, Dec 15, 2021 at 08:18:53AM +0000, Amir Gonnen wrote: > Before sending a patch, I would like to check if it's of interest to the > community. > > My goal is to simulate a mixed architecture system. > Today QEMU strongly assumes that the simulated system is a *single > architecture*. > Changing this assumption and supporting mixed architecture in QEMU proved to > be > non-trivial and may require significant development effort. Common code such > as > TCG and others explicitly include architecture specific header files, for > example.
Hi Amir, Simulating heterogenous machines comes up from periodically. So far no one has upstreamed a solution but there is definitely interest. I suggest going ahead and posting the code even if it's not cleaned up. > A possible solution, discussed on https://stackoverflow.com/q/63229262/619493 > is to > separate the simulation to multiple processes (as done by Xilinx) and to use > some form > of Interprocess Communication channel between them. > Such solution has several disadvantages: > > - Harder to synchronize simulation between processes > - Performance impact of Interprocess Communication > - Harder to debug, profile and maintain > > Instead, I would like to suggest a new approach we use at Neuroblade to > achieve this: > Build QEMU as a shared library that can be loaded and used directly in a > larger simulation. > Today we build qemu-system-nios2 shared library and load it from > qemu-system-x86_64 in order > to simulate an x86_64 system that also consists of multiple nios2 cores. > In our simulation, two independent "main" functions are running on different > threads, and > simulation synchronization is reduced to synchronizing threads. > > To achieve this, I needed to do the following changes in QEMU: > > 1. Avoid Glib global context. Use a different context (g_main_context_new) > for each QEMU instance. > 2. Change meson.build to build QEMU as a shared library (with PIC enabled for > static libraries) > 3. Define a C API for the library and export it (with a -Wl,--version-script) > > These changes seem enough for simulating mixed architecture system on a > single process. > > If this approach sounds useful, I'll be happy to send patches. > I'd appreciate if you could provide your feedback! I'm curious how much synchronization and IPC there is between the QEMU shared libraries? I would have guessed that the pain of making communication work efficiently between processes would be less than the pain of solving global state bugs related to shared libraries within a single process. Were there issues with POSIX signal handlers? Stefan
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