On Tue, Mar 17, 2020 at 11:29 PM Andreas Dilger adilger@dilger.ca wrote:
That said, I'd think it would be preferable for ease of use and compatibility that applications didn't have to be modified (e.g. have QEMU or glibc internally set PER_LINUX32 for this process before the 32-bit syscall is called, given that it knows whether it is emulating a 32-bit runtime or not).
I think the plan is that QEMU set this, either directly when you run qemu-user or through the binfmt handler. https://www.kernel.org/doc/html/latest/admin-guide/binfmt-misc.html
IIUC the binfmt handler is invoked when you try to execute ELF so-and-so-for-arch-so-and-so when you are not that arch yourself. So that can set up this personality.
Not that I know how the binfmt handler works, I am just assuming that thing is some program that can issue syscalls. It JustWorks for me after installing the QEMU packages...
The problem still stands that userspace need to somehow inform kernelspace that 32bit is going on, and this was the best I could think of.
Yours, Linus Walleij