On 24/03/2021 20.24, Joe Perches wrote:
On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:
On 24/03/2021 18.20, Joe Perches wrote:
Maybe it's better to output non PTR_ERR %pe uses as decimal so this sort of code would work.
No, because that would leak the pointer value when somebody has accidentally passed a real kernel pointer to %pe.
I think it's not really an issue.
_All_ code that uses %p<foo> extensions need inspection anyway.
There are now a bunch of sanity checks in place that catch e.g. an ERR_PTR passed to an extension that would derefence the pointer; enforcing that only ERR_PTRs are passed to %pe (or falling back to %p) is another of those safeguards.
It's already possible to intentionally 'leak' the ptr value by using %pe, -ptr so I think that's not really an issue.
Huh, what? I assume -ptr is shorthand for (void*)-(unsigned long)ptr. How would that leak the value if ptr is an ordinary kernel pointer? That's not an ERR_PTR unless (unsigned long)ptr is < 4095 or so.
If you want to print the pointer value just do %px. No need for silly games. What I'm talking about is preventing _un_intentionally leaking a valid kernel pointer value. So no, a non-ERR_PTR passed to %pe is not going to be printed as-is, not in decimal or hexadecimal or roman numerals.
If the code wants a cute -EFOO string explaining what's wrong, what about "%pe", ERR_PTR(mux < 0 : mux : -ERANGE)? Or two separate error messages
if (mux < 0) ... else if (mux >= ARRAY_SIZE()) ...
Multiple tests, more unnecessary code, multiple format strings, etc...
Agreed, I'm not really advocating for the latter; the former suggestion is IMO a pretty concise way of providing useful information in dmesg.
Rasmus