linux-kernel - Re: [PATCH 2/2] elf: print userspace address with %lx

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Date:   Sat, 16 Mar 2019 09:28:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] elf: print userspace address with %lx

On Fri 15-03-19 19:06:56, Alexey Dobriyan wrote:
> On Fri, Mar 15, 2019 at 07:53:27AM +0100, Michal Hocko wrote:
> > On Thu 14-03-19 23:45:48, Alexey Dobriyan wrote:
> > > Use %lx, save a cast.
> > > 
> > > "addr" is userspace address so using (and mangling) pointer was never
> > > necessary.
> > 
> > There shouldn't be any mangling AFAIU. Documentation for pointer()
> > says
> > 
> >  * - 'x' For printing the address. Equivalent to "%lx".
> 
> The implication of using %p/%px is that the address is kernel pointer
> which should or should not be mangled.

And px is not mangled AFAICS.

> But "map_addr" is not a kernel pointer.

Which should be irrelevant. It is a pointer and my understanding is that
%p$FOO should be used preferably for any pointers.

> And it saves a cast.

Is this really such an improvement? Why?

> > > --- a/fs/binfmt_elf.c
> > > +++ b/fs/binfmt_elf.c
> > > @@ -376,8 +376,8 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
> > >  		map_addr = vm_mmap(filep, addr, size, prot, type, off);
> > >  
> > >  	if ((type & MAP_FIXED_NOREPLACE) && map_addr == -EEXIST)
> > > -		pr_info("%d (%s): Uhuuh, elf segment at %px requested but the memory is mapped already\n",
> > > -			task_pid_nr(current), current->comm, (void *)addr);
> > > +		pr_info("%d (%s): Uhuuh, elf segment at %lx requested but the memory is mapped already\n",
> > > +			task_pid_nr(current), current->comm, addr);

-- 
Michal Hocko
SUSE Labs