Hi Erik, On 01/17/2014 01:33 AM, Erik de Castro Lopo wrote: > Hi all, > > I'm currently working on implementing a missing part of a linux-user > syscall. This syscall includes a function pointer for a callback. > > If one has a 64 bit user space emulation running on a 32 bit host, > how does one handle the fact that the pointer might be 64 bits? > > Does the fact that the 32 bit host can only ever give out 32 bit > addreses to the 64 bit guest just cancel out the possibility of > any problems?
Not that I know anything about QEMU internals yet, but just for fun here's my armchair philosophizing. My interpretation of the scenario you describe is that some function exists in a 64-bit instruction set architecture. QEMU/TCG has translated it to the host's native 32-bit ISA for actual execution. It seems like you should be exclusively communicating the address of the 32-bit translated version to the host kernel. I don't think the host kernel could do anything useful with a pointer to the foreign ISA version, even if it got the address right. Regards, Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation.
