Re: [PATCH 0/7] use struct pt_regs based syscall calling for x86-64

Ingo Molnar
2018-03-30T10:16:08Z

* Dominik Brodowski <linux@dominikbrodowski.net> wrote:

> A few questions remain, from important stuff to bikeshedding:
>
> 1) Is it acceptable to pass the existing struct pt_regs to the sys_*()
> kernel functions in emulate_vsyscall(), or should it use a hand-crafted
> struct pt_regs instead?

I think so: we already have task_pt_regs() which gives access to the real return
registers on the kernel stack.

I think as long as we constify the pointer, we should pass in the real thing.

> 2) Is it the right approach to generate the __sys32_ia32_*() names to
> include in the syscall table on-the-fly, or should they all be listed
> in arch/x86/entry/syscalls/syscall_32.tbl ?

I think as a general principle all system call tables should point to the
first-hop wrapper symbol name (i.e. __sys32_ia32_*() in this case), not to the
generic symbol name - even though we could generate the former from the latter.

The more indirection in these tables, the harder to read they become I think.

> 3) I have chosen to name the default 64-bit syscall stub sys_*(), same as
> the "normal" syscall, and the IA32_EMULATION compat syscall stub
> compat_sys_*(), same as the "normal" compat syscall. Though this
> might cause some confusion, as the "same" function uses a different
> calling convention and different parameters on x86, it has the
> advantages that
> - the kernel *has* a function sys_*() implementing the syscall,
> so those curious in stack traces etc. will find it in plain
> sight,
> - it is easier to handle in the syscall table generation, and
> - error injection works the same.

I don't think there should be a symbol space overlap, that will only lead to
confusion. The symbols can be _similar_, with a prefix, underscores or so, but
they shouldn't match I think.

> The whole series is available at
>
> https://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux.git syscalls-WIP

BTW., I'd like all these bits to go through the x86 tree.

What is the expected merge route of the generic preparatory bits?

Thanks,

Ingo