Hi Florian, Em 02/11/2024 18:58, Florian Weimer escreveu:
* André Almeida:1) x86 apps can have 32bit pointers robust lists. For a x86-64 kernel this is not a problem, because of the compat entry point. But there's no such compat entry point for AArch64, so the kernel would do the pointer arithmetic wrongly. Is also unviable to userspace to keep track every addition/removal to the robust list and keep a 64bit version of it somewhere else to feed the kernel. Thus, the new interface has an option of telling the kernel if the list is filled with 32bit or 64bit pointers.The size is typically different for 32-bit and 64-bit mode (12 vs 24 bytes). Why isn't this enough to disambiguate?
Right, so the idea would be to use `size_t len` from the syscall arguments for that?
2) Apps can set just one robust list (in theory, x86-64 can set two if they also use the compat entry point). That means that when a x86 app asks FEX-Emu to call set_robust_list(), FEX have two options: to overwrite their own robust list pointer and make the app robust, or to ignore the app robust list and keep the emulator robust. The new interface allows for multiple robust lists per application, solving this.Can't you avoid mixing emulated and general userspace code on the same thread? On emulator threads, you have full control over the TCB.
FEX can't avoid that because it doesn't do a full system emulation, it just does instructions translation. FEX doesn't have full control over the TCB, that's still all glibc, or whatever other dynamic linker is used.
