linux-kernel - Re: linux-next: Tree for Oct 31 (vboxguest)

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Date:   Sun, 4 Nov 2018 11:43:44 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Changbin Du <changbin.du@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: linux-next: Tree for Oct 31 (vboxguest)

On Sat, Nov 3, 2018 at 12:55 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On 11/2/18, Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
> > On Thu, Nov 1, 2018 at 11:32 PM Changbin Du <changbin.du@...il.com> wrote:
> >> On Thu, Nov 01, 2018 at 12:32:48PM +0900, Masahiro Yamada wrote:
> >
> > How about clang?
> >
> > For clang, -Og might be equivalent to -O1 at this moment, but I am not
> > sure.
> >
> > In my understanding, Clang does not inline functions marked with 'static
> > inline'
> > for -Og (or -O1) optimization level.
> >
> > Theoretically, 'inline' keyword is a just hint for the compiler, after all.
>
> I think this means that we cannot build the kernel in that configuration,
> at least with CONFIG_OPTIMIZE_INLINING=y. Without that option,
> every 'inline' becomes 'always_inline'.
>

Sorry, I missed that fact.


At this moment of time, it is OK given the following:

 - CONFIG_OPTIMIZE_INLINING is defined only for x86
 - Clang cannot build x86 due to missing asm-goto


However, Clang with -Og
does not inline even such simple code like this:


-----test code------
static inline int foo(int x)
{
        return x;
}

int bar(int x)
{
        return foo(x);
}
-------------------



$ clang -Og -c -o bar.o  bar.c
$ objdump -d  bar.o
bar.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <bar>:
   0: eb 0e                jmp    10 <foo>
   2: 66 2e 0f 1f 84 00 00 nopw   %cs:0x0(%rax,%rax,1)
   9: 00 00 00
   c: 0f 1f 40 00          nopl   0x0(%rax)

0000000000000010 <foo>:
  10: 89 f8                mov    %edi,%eax
  12: c3                    retq



-- 
Best Regards
Masahiro Yamada