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

Joe Perches
2014-12-07T12:30:20Z

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.