Re: 64-bit syscall ABI issue

Re: 64-bit syscall ABI issue

[David Miller]

From: "Joseph S. Myers" <joseph@codesourcery.com>
Date: Mon, 4 Jun 2007 20:56:57 +0000 (UTC)

[ added linux-arch which is a great place to discuss these
  kinds of issues. ]

> What should the kernel syscall ABI be in such cases (any case where the 
> syscall implementations expect arguments narrower than registers, so 
> mainly 32-bit arguments on 64-bit platforms)?  There are two obvious 
> possibilities:

In general we've taken the stance that the syscall dispatch
should create the proper calling environment for C code
implementing the system calls, and this thus means properly
sign and zero extending the arguments as expected by the C
calling convention.

Re: 64-bit syscall ABI issue

[H. Peter Anvin]

David Miller wrote:
> From: "Joseph S. Myers" <joseph@codesourcery.com>
> Date: Mon, 4 Jun 2007 20:56:57 +0000 (UTC)
> 
> [ added linux-arch which is a great place to discuss these
>   kinds of issues. ]
> 
>> What should the kernel syscall ABI be in such cases (any case where the 
>> syscall implementations expect arguments narrower than registers, so 
>> mainly 32-bit arguments on 64-bit platforms)?  There are two obvious 
>> possibilities:
> 
> In general we've taken the stance that the syscall dispatch
> should create the proper calling environment for C code
> implementing the system calls, and this thus means properly
> sign and zero extending the arguments as expected by the C
> calling convention.

This is, in fact, rather fundamental (some ABIs don't require sign or
zero extension, e.g. x86-64); otherwise libc's job becomes a whole lot
harder.

	-hpa