[ Ingo, Thomas - see the whole series on linux-kernel ]
On Thu, 15 Nov 2007, Ulrich Drepper wrote:
>
> This part adds support for sys_indirect on x86 and x86-64.
The thing is, not all system calls can do this.
Some system calls are magic, and don't just take the arguments in
registers: they also care about the actual stack pointer and the whole
pt_regs struct when returning to user mode.
So this does need more infrastructure: some way of marking which system
calls cannot be executed indirectly.
The magic system calls are things like:
- sys_iopl() - this one changes the eflags value restored on iret
- execve/clone/vfork() - need direct access to pt_regs
- vm86() - does magic with the stack, cares about pt_regs
- sigreturn - magic pt_regs accesses again
and there may be others I have forgotten about.
Calling these system calls from C code will just corrupt the kernel stack,
and is a big big no-no.
Linus
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