Messages in this thread | | | Date | Wed, 12 Aug 2009 17:27:27 +0800 | Subject | Is compat_sys_ioctl called when both kernel and userland are 64bit ? | From | april <> |
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Hi all:
I am doing something to support 32bit userland and 64bit kernel. I know compat_sys_ioctl will be called if 32bit userland send ioctl to 64bit kernel.
The compat ioctl do some conversion(suppose I provide those ioctls). For example: if a struct has a field type is long or a pointer,which the size is different between userland and kernel
I notice in the x86_64_defconfig file: CONFIG_X86_64=y CONFIG_IA32_EMULATION=y and in "trap_init" function, #ifdef CONFIG_IA32_EMULATION set_system_intr_gate(IA32_SYSCALL_VECTOR, ia32_syscall); set_bit(IA32_SYSCALL_VECTOR, used_vectors); #endif
it seems when a kernel is built to x86_64, whenever a ioctl called ,the call flow will be ia32_syscall -->compat_sys_ioctl->compat ioctl(if provided) but I have some doubt:
My question is: 1. Is compat_sys_ioctl called when both kernel and userland are 64bit (suppose I provide those compat ioctl functions)? if so, it may have problem, for the compat ioctl suppose userland is 32bit, and do the conversion, if a field is unsinged long or a pointer, it will do the wrong things .
If not, how kernel knows the driver is 32bit or 64bit?
2. when using mmap, the 64bit kernel will return a 64bit address, and a userland(32bit) application can only get the lower 32bit, it can work when the memory is not large.
Is kernel do some conversion? or fortunately the higher 32bit is 00000000 ?
Thanks
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