Re: [PATCH V11 4/5] vsprintf: add printk specifier %px

Linus Torvalds
2017-12-06T01:59:24Z

On Tue, Dec 5, 2017 at 5:36 PM, Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
> I see some %p-s being used in _supposedly_ important output,
> like arch/x86/mm/fault.c
>
> show_fault_oops(struct pt_regs *regs, unsigned long error_code,
> unsigned long address)
> ...
> printk(KERN_CONT " at %p\n", (void *) address);
> printk(KERN_ALERT "IP: %pS\n", (void *)regs->ip);

So %pS isn't %p, and shows the symbolic name.

But yes, that "at %p" should definitely be %px.

In fact, it used to be a "%08lx" - and the value we print out is
"unsigned long - but then when we unified the 32- and 64-bit
architectures, using "%p" and a cast was a convenient way to unify the
32-bit %08lx and the 16-bit %016lx formats.

Will fix.

> a quick %p grep gives me the following list:
...
> or is it OK to show hashes instead of pgd or pmd pointers?

So my gut feel is that those printouts should probably just be
removed. They have some very old historical reasons: we've printed out
the page directory pointers (and followed the page tables) since at
least back in the 1.1.x days. This is from the 1.1.7 patch, back when
mm/memory.c was all about x86:

+ printk(KERN_ALERT "current->tss.cr3 = %08lx, %%cr3 = %08lx\n",
+ current->tss.cr3, user_esp);
+ user_esp = ((unsigned long *) user_esp)[address >> 22];
+ printk(KERN_ALERT "*pde = %08lx\n", user_esp);

so it's more historical than sensible, I think.

Linus