On Sun, Nov 04, 2018 at 11:43:44AM +0900, Masahiro Yamada wrote:
> On Sat, Nov 3, 2018 at 12:55 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> >
> > On 11/2/18, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote:
> > > On Thu, Nov 1, 2018 at 11:32 PM Changbin Du <changbin.du@xxxxxxxxx> 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
>
>
I see. Thanks for your explanation. So I think we should disable
CONFIG_DEBUG_EXPERIENCE for clang. Do you know how to distinguish
different copmilers in Kconfig?
>
> --
> Best Regards
> Masahiro Yamada
--
Thanks,
Changbin Du
