Re: [PATCH v2 1/6] net-PPP: Replacement of a printk() call by pr_warn() in mppe_rekey()

Julia Lawall
2014-12-07T12:36:14Z

On Sun, 7 Dec 2014, Joe Perches wrote:

> On Sun, 2014-12-07 at 11:44 +0100, Julia Lawall wrote:
> > > A negative to that approach is inlined functions would
> > > take the function name of the parent not keep the
> > > inlined function name.
> >
> > I tried the following:
> >
> > #include <stdio.h>
> >
> > inline int foo() {
> > printf("%s %x\n",__func__,0x12345);
> > }
> >
> > int main () {
> > foo();
> > }
> >
> > The assembly code generated for main is:
> >
> > 0000000000400470 :
> > 400470: b9 45 23 01 00 mov $0x12345,%ecx
> > 400475: ba 4b 06 40 00 mov $0x40064b,%edx
> > 40047a: be 44 06 40 00 mov $0x400644,%esi
> > 40047f: bf 01 00 00 00 mov $0x1,%edi
> > 400484: 31 c0 xor %eax,%eax
> > 400486: e9 d5 ff ff ff jmpq 400460 <__printf_chk@plt>
> >
> > That is, the call to foo seems tom be inlined.
> >
> > But the output is:
> >
> > foo 12345
> >
> > So it seems that __func__ is determined before inlining.
>
> True, and that's what I intended to describe.
>
> If you did that with a kernel module and replaced
> "%s, __func__" with "%pf, __builtin_return_address(0)"
> when built with kallsyms you should get:
>
> "modname 12345" when most would expect "foo 12345"
>
> when built without kallsyms, that output should be
> " 12345"
>
> but the object code should be smaller.

OK. But the semantic patch is only using __func__ and only in cases where
the string wanted is similar to the name of the current function, so I
think it should be OK?

julia