syscall_linkage

syscall_linkage

[Zoltan Menyhart]

Can somebody explain me, please, what the difference is between an
__attribute__((syscall_linkage)) call and a regular one ?

The Itanium Software Conventions & Runtime Architecture Guide does
not say a word about it, does it mean it is a non standard way to
pass parameters ?

What registers need / do not need to be saved with respect to what
is written in the Intel book ?

Thanks,

Zoltán Menyhárt

Re: syscall_linkage

[Stephane Eranian]

Hi,

On Thu, Apr 08, 2004 at 05:54:40PM +0200, Zoltan Menyhart wrote:
> Can somebody explain me, please, what the difference is between an
> __attribute__((syscall_linkage)) call and a regular one ?
> 

It indicates to the compiler that the arguments of the function 
are to be treated read-only. If they need to be modified, then a
copy is made into  other registers. This is necessary for the 
system call entry points because some syscalls can be restarted
and they need to restart we the orginal values. Remember that
all syscall arguments are passed in registers AND the registers
come straight from the user level, i.e., they are never copied.


> The Itanium Software Conventions & Runtime Architecture Guide does
> not say a word about it, does it mean it is a non standard way to
> pass parameters ?
> 
> What registers need / do not need to be saved with respect to what
> is written in the Intel book ?
> 
> Thanks,
> 
> Zoltán Menyhárt
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-- 

-Stephane

Re: syscall_linkage

[David Mosberger]

Zoltan,

The quick summary can be found in asm-ia64/ptrace.h.
Also, my book has a fairly extensive discussion of how machine-state
is handled on ia64 linux.

	--david

>>>>> On Thu, 08 Apr 2004 17:54:40 +0200, Zoltan Menyhart <Zoltan.Menyhart_AT_bull.net@nospam.org> said:

  Zoltan> Can somebody explain me, please, what the difference is between an
  Zoltan> __attribute__((syscall_linkage)) call and a regular one ?

  Zoltan> The Itanium Software Conventions & Runtime Architecture Guide does
  Zoltan> not say a word about it, does it mean it is a non standard way to
  Zoltan> pass parameters ?

  Zoltan> What registers need / do not need to be saved with respect to what
  Zoltan> is written in the Intel book ?

Re: syscall_linkage

[Jim Wilson]

On Thu, 2004-04-08 at 08:54, Zoltan Menyhart wrote:
> Can somebody explain me, please, what the difference is between an
> __attribute__((syscall_linkage)) call and a regular one ?

It also prohibits use of input registers for local values, thus helping
to prevent kernel data from accidentally leaking back to application
code.  The input registers will be visible to the caller after the
syscall returns because of the register windows.

See the gcc code that implements syscall_linkage in
gcc/config/ia64/ia64.c.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com