Re: [PATCH] mm: Mark create_huge_pmd() inline to prevent build failure

From: Arnd Bergmann
Date: Wed Jul 12 2017 - 03:23:02 EST

On Wed, Jul 12, 2017 at 8:57 AM, Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
> With gcc 4.1.2:
> mm/memory.o: In function `create_huge_pmd':
> memory.c:(.text+0x93e): undefined reference to `do_huge_pmd_anonymous_page'
> Converting transparent_hugepage_enabled() from a macro to a static
> inline function reduced the ability of the compiler to remove unused
> code.
> Fix this by marking create_huge_pmd() inline.
> Fixes: 16981d763501c0e0 ("mm: improve readability of transparent_hugepage_enabled()")
> Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

> ---
> Interestingly, create_huge_pmd() is emitted in the assembler output, but
> never called.

I've never seen this before either. I know that early gcc-4 compilers
would do this
when a function is referenced from an unused function pointer, but not with
a compile-time constant evaluation. I guess that transparent_hugepage_enabled
is just slightly more complex than it gcc-4.1 can handle here.