linux-kernel - Re: [PATCH v2 17/31] arm64: System calls handling

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Message-ID: <20120821175122.GI12708@arm.com>
Date:	Tue, 21 Aug 2012 18:51:22 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH v2 17/31] arm64: System calls handling

On Wed, Aug 15, 2012 at 03:22:16PM +0100, Arnd Bergmann wrote:
> On Tuesday 14 August 2012, Catalin Marinas wrote:
> 
> > +
> > +/* This matches struct stat64 in glibc2.1, hence the absolutely
> > + * insane amounts of padding around dev_t's.
> > + * Note: The kernel zero's the padded region because glibc might read them
> > + * in the hope that the kernel has stretched to using larger sizes.
> > + */
> > +struct stat64 {
> > +	compat_u64	st_dev;
> > +	unsigned char   __pad0[4];
> 
> The comment above struct stat64 is completely irrelevant here. I would instead
> explain why you need your own stat64 in the first place.

OK, I added a comment. It's only needed for compat.

> > +int kernel_execve(const char *filename,
> > +		  const char *const argv[],
> > +		  const char *const envp[])
> 
> Al Viro was recently talking about a generic implementation of execve.
> I can't find that now, but I think you should use that.

I've seen these but I'm waiting for the generic sys_execve and
kernel_execve to get into mainline before switch arch/arm64 to them.

> > +asmlinkage long sys_mmap(unsigned long addr, unsigned long len,
> > +			 unsigned long prot, unsigned long flags,
> > +			 unsigned long fd, off_t off)
> > +{
> > +	if (offset_in_page(off) != 0)
> > +		return -EINVAL;
> > +
> > +	return sys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT);
> > +}
> 
> I think
> 
> #define sys_mmap sys_mmap_pgoff 

There are slightly different semantics with the last argument of
sys_mmap() which takes a byte offset. The sys_mmap_pgoff() function
takes the offset shifted by PAGE_SHIFT (which is the same as sys_mmap2).

Looking at the other architectures, it makes sense to use a generic
sys_mmap() implementation similar to the one above (or the ia-64, seems
to be the most complete).

-- 
Catalin
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