Re: [PATCH] kbuild: Use -nostdinc in compile tests

Michal Marek
2014-11-25T21:53:09Z

Dne 6.11.2014 v 01:58 Ben Hutchings napsal(a):
> gcc 4.8 and later include <stdc-predef.h> by default. In some
> versions of eglibc that includes <bits/predefs.h>, but that may be
> missing when building with a biarch compiler. Also <stdc-predef.h>
> itself could be missing as we are only trying to build a kernel, not
> userland.
>
> The -nostdinc option disables this, though it isn't explicitly
> documented. This option is already used when actually building
> the kernel, but not by cc-option and other tests. This can result
> in silently miscompiling the kernel.
>
> References: https://bugs.debian.org/717557
> References: https://bugs.debian.org/726861
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---
> This specific issue appeared and then was fixed in Debian about a year
> ago, but it seems like it can also affect cross-builds.
>
> It may also be worth adding some sort of sanity test, so we stop
> immediately if $(cc-option $(empty),broken) yields 'broken'.
>
> Ben.
>
> Makefile | 4 +++-
> scripts/Kbuild.include | 15 ++++++++-------
> 2 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index ffc1ce2..c0fbf67 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -619,6 +619,8 @@ endif
> # Tell gcc to never replace conditional load with a non-conditional one
> KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
>
> +NOSTDINC_FLAGS += -nostdinc
> +
> ifdef CONFIG_READABLE_ASM
> # Disable optimizations that make assembler listings hard to read.
> # reorder blocks reorders the control in the function
> @@ -742,7 +744,7 @@ KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
> endif
>
> # arch Makefile may override CC so keep this after arch Makefile is included
> -NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
> +NOSTDINC_FLAGS += -isystem $(shell $(CC) -print-file-name=include)

Why not simply move the whole assignment up? Also, there are two
cc-option tests and one cc-disable-warning test before the first part
assignment. Looks like a result of a mismerge.

Michal