diff mbox series

[37/46] Compiler attributes, lto: disable __flatten with LTO

Message ID 20221114114344.18650-38-jirislaby@kernel.org
State New
Headers
Series gcc-LTO support for the kernel |

Commit Message

Jiri Slaby Nov. 14, 2022, 11:43 a.m. UTC 
  From: Andi Kleen <andi@firstfloor.org>

Using __flatten causes a simple gcc 12 LTO build not fit into 16GB
anymore. Disable flatten with LTO. With gcc 12, the build still does not
finish linking in 10 minutes, eating 40GB of RAM at that point.

There is an upstream bug about this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107014

Until this is resolved, simply disable __flatten with LTO.

In the future, instead of this patch, we should likely drop __flatten
and its only user (pcpu_build_alloc_info()) and use always_inline to all
functions which shall be inlined there.

Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Martin Liska <mliska@suse.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 include/linux/compiler_attributes.h | 5 +++++
 1 file changed, 5 insertions(+)

Comments

Miguel Ojeda Nov. 14, 2022, 5:01 p.m. UTC | #1 
On Mon, Nov 14, 2022 at 12:45 PM Jiri Slaby (SUSE) <jirislaby@kernel.org> wrote:
>
> +#ifndef CONFIG_LTO_GCC
>  # define __flatten                     __attribute__((flatten))
> +#else
> +/* Causes very large memory use with gcc in LTO mode */
> +# define __flatten
> +#endif

Currently, this header avoids attributes that depend on configuration
options on purpose (see the comment at the top), so it would be best
to move it elsewhere, e.g. `compiler_types.h`.

Though I feel bad about having to move this attribute out since it is
just that config option compared to other more involved bits in
`compiler_types.h`... :(

Cheers,
Miguel
diff mbox series

Patch

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index be6c71fd5ebb..09cf8eebcb0d 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -229,7 +229,12 @@ 
  * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
  * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
  */
+#ifndef CONFIG_LTO_GCC
 # define __flatten			__attribute__((flatten))
+#else
+/* Causes very large memory use with gcc in LTO mode */
+# define __flatten
+#endif
 
 /*
  * Note the missing underscores.