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Re: LTP testing

To: Carsten Langgaard <carstenl@mips.com>
Subject: Re: LTP testing
From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Date: Tue, 25 Jun 2002 16:56:12 +0200 (MET DST)
Cc: Ralf Baechle <ralf@oss.sgi.com>, "linux-mips@oss.sgi.com" <linux-mips@oss.sgi.com>
In-reply-to: <3D187BC8.17765700@mips.com>
Organization: Technical University of Gdansk
Sender: owner-linux-mips@oss.sgi.com
On Tue, 25 Jun 2002, Carsten Langgaard wrote:

> > Linux platforms do it this way, e.g. Alpha and IA-64.  A SIGSEGV is a
> > valid response for an invalid address.  Remember you test pipe(3) and not
> > pipe(2).
> 
> I'm not sure that you mean by pipe(2) and pipe(3), but according to my man
> page, pipe should return with EFAULT in this case.

 pipe(2) is a syscall, while pipe(3) is a library call (see `man 2 intro'
and `man 3 intro', respectively).  You rarely access syscalls directly --
the system library usually does this for you.  Depending on a system
certain library functions may be trivial syscall wrappers, invoke a number
of syscalls (see e.g. the stat() family) or be implemented entirely in the
userland. 

> ERRORS
>        EMFILE Too  many  file  descriptors are in use by the pro­
>               cess.
>        ENFILE The system file table is full.
>        EFAULT filedes is not valid.

 Yep, this denotes such an error is possible and under what conditions.  I
don't think it actually mandates it, at least it's not expressed
explicitly.  Anyway, it's valid for i386 and possibly nothing else.  Look
at the system version it refers to -- my version is: "Linux 0.99.11 23
July 1993".

 A brief search of the web for "EFAULT pipe" reveals confirms others agree
with me -- the error is not mandatory (the EFAULT vs SIGSEGV issue was
discussed a few times at least in various contexts -- go search the web). 

 I believe a SIGSEGV is saner, too -- this way it's harder for an error
resulting from passing an invalid pointer to remain unnoticed (consider
some code that passes a pointer to read-only memory and fails to check a
result of pipe()).

 If still in doubt, you may try to discuss the LTP result at
<linux-kernel@vger.kernel.org>.  I don't think anybody wants to rewrite
pipe(2) for all the platforms that handle it our way. 

  Maciej

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +



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