Well certainly, I know they are different executables. I'm just trying to understand how the different targets work.
By subsumes, I mean that just looking at the meson.build for i386, you can see that there are files added to the i386_ss, but not visibly added to the softmmu target. But the softmmu target has those files built whenever you configure and build it. And right that's what I thought. What I'm thinking is that the i386_ss is compiled with a different implementation for those call backs based on the target and the user emulation. On Thu, Jul 15, 2021 at 11:17 AM Peter Maydell <peter.mayd...@linaro.org> wrote: > On Thu, 15 Jul 2021 at 16:59, Kenneth Adam Miller > <kennethadammil...@gmail.com> wrote: > > > > If I am right, the softmmu/system build target for each architecture > subsumes the source of the user target. > > I'm not sure what you mean by "subsumes" here. Some code in > QEMU is compiled into both the system and usermode emulators > (eg most of the CPU emulation code). Some is system mode only > (eg the device models). Some is usermode only (eg the emulation > of various system calls). > > > What I was wondering is, if the user layer of qemu is used by the > > user target, and by user layer I mean the using contents of linux-user, > > then how does the system target receive the user programs instead > > of the qemu user emulation layer even within a guest that is an > > entire OS? > > qemu-i386 and qemu-system-i386 are different executables. > They're built differently, and what happens when a usermode > program running inside a Linux guest inside qemu-system-i386 > executes a syscall instruction is completely different from > what happens when a program running on qemu-i386 executes that > instruction. Specifically, there are different versions of the > x86_cpu_do_interrupt() function: the one for system emulation does > "update the guest CPU state in the way that the real CPU does when > an int 0x80 is executed", and the one for usermode emulation does > "raise a fake exception that will cause execution to return from > the call to cpu_exec() in linux-user/i386/cpu_loop.c:cpu_loop() > so it can emulate a syscall". > > thanks > -- PMM >
