On Tue, Nov 8, 2016 at 8:16 AM, Linus Torvalds <[email protected]> wrote: > So I definitely approve of the change, but I wonder if we should go > one step further: > > On Mon, Nov 7, 2016 at 1:26 PM, Steven Rostedt <[email protected]> wrote: >> >> extern int task_current_syscall(struct task_struct *target, long *callno, >> - unsigned long args[6], unsigned int maxargs, >> - unsigned long *sp, unsigned long *pc); >> + unsigned long args[6], unsigned long *sp, >> + unsigned long *pc); > > The thing is, in C, having an array in a function declaration is > pretty much exactly the same as just having a pointer, so from a type > checking standpoint it doesn't really help all that much (but from a > "human documentation" side the "args[6]" is much better than "*args"). > > However, what would really help type checking is making it a > structure. And maybe that structure could just contain "callno", "sp" > and "pc" too? That would not only fix the type checking, it would make > the calling convention even cleaner. Just have one single structure > that contains all the relevant data.
I would propose calling this 'struct seccomp_data'. > > For example, kernel/seccomp.c does this instead: > > sd->nr = syscall_get_nr(task, regs); > sd->arch = syscall_get_arch(); > syscall_get_arguments(task, regs, 0, 6, args); > sd->args[0] = args[0]; > sd->args[1] = args[1]; > sd->args[2] = args[2]; > sd->args[3] = args[3]; > sd->args[4] = args[4]; > sd->args[5] = args[5]; > sd->instruction_pointer = KSTK_EIP(task); It's a bit hard to tell from seccomp.c, but x86 carefully arranges for that code to never get run -- instead the entry code supplies a struct seccomp_data. Other arches could follow suit for a nice speedup. --Andy
