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

From: Joe Perches <[email-masked]>
Date: Sun, 07 Dec 2014 04:30:13 -0800

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 <main>:
>   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
"<address> 12345"

but the object code should be smaller.