[PATCH 2/2] elf: print userspace address with %lx

[PATCH 2/2] elf: print userspace address with %lx

[Alexey Dobriyan]

Use %lx, save a cast.

"addr" is userspace address so using (and mangling) pointer was never
necessary.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/binfmt_elf.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- 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);
 
 	return(map_addr);
 }

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

[Michal Hocko]

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".

> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
>  fs/binfmt_elf.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- 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);
>  
>  	return(map_addr);
>  }

-- 
Michal Hocko
SUSE Labs

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

[Alexey Dobriyan]

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. But "map_addr" is not a kernel
pointer. And it saves a cast.

> > --- 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);

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

[Michal Hocko]

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