Messages in this thread | | | Date | Wed, 11 Feb 2009 16:01:44 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it |
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* Brian Gerst <brgerst@gmail.com> wrote:
> On Wed, Feb 11, 2009 at 2:41 AM, Tejun Heo <tj@kernel.org> wrote: > > Hello, Brian. > > > > Brian Gerst wrote: > >> Some syscalls need to access the pt_regs structure, either to copy > >> user register state or to modifiy it. This patch adds stubs to load > >> the address of the pt_regs struct into the %eax register, and changes > >> the syscalls to regparm(1) to receive the pt_regs pointer as the > >> first argument. > > > > Heh... neat. Just one question. > > > >> -asmlinkage long sys_iopl(unsigned long regsp) > >> +ptregscall long sys_iopl(struct pt_regs *regs, unsigned int level) > >> { > >> - struct pt_regs *regs = (struct pt_regs *)®sp; > >> - unsigned int level = regs->bx; > > > > Here and at other places where the function takes more than one > > arguments, wouldn't it be better to just take *regs and use other > > parameters from regs? That way we won't have to worry about gcc > > corrupting register frame at all and I think it's cleaner that way. > > Expanding the parameters is good documentation. [...]
Well, that way we shuffle the parameter expansion into assembly code, instead of creating it as a local variable in the C function.
The latter sure looks better documented, and less error-prone as well, right? The compiler might also be able to optimize it some. (and we save one instruction in any case)
Ingo
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