[Buildroot] [PATCH v2 2/2] toolchain/toolchain-wrapper: handle __FILE__ macro for reproducibility

[Romain Naour]

Hi Atharva,

Le 31/08/2019 à 20:01, Atharva Lele a écrit :
> Many tools use __FILE__ for debugging and __FILE__ captures the build path.
> This results in non-reproducible images when building in different directories.

Based on the commit log in gcc adding this option [1], -ffile-prefix-map also
remap file names in __BASE_FILE__ and __builtin_FILE().

Specifying -ffile-prefix-map option is equivalent to specifying all the
individual options -f*-prefix-map (-fmacro-prefix-map and -fdebug-prefix-map).

[1]
https://github.com/gcc-mirror/gcc/commit/859b51f83662d01e4f158ea9327db9ca37fe70b3

> 
> If the config uses GCC 8 or above, we use -ffile-prefix-map=old=new and let gcc
> take care of the path remapping in __FILE__. Since GCC versions before v8 did
> not have this feature, we use a dummy string in that case.
> 
> Signed-off-by: Atharva Lele <itsatharva at gmail.com>
> ---
> Changes v2:
>   - New patch
> ---
>  toolchain/toolchain-wrapper.mk | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/toolchain/toolchain-wrapper.mk b/toolchain/toolchain-wrapper.mk
> index 88695a5b2d..6d0ae2c85b 100644
> --- a/toolchain/toolchain-wrapper.mk
> +++ b/toolchain/toolchain-wrapper.mk
> @@ -23,6 +23,11 @@ TOOLCHAIN_WRAPPER_OPTS = \
>  
>  ifeq ($(BR2_REPRODUCIBLE),y)
>  TOOLCHAIN_WRAPPER_OPTS += -Wl,--build-id=none
> +ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_8),y)
> +TOOLCHAIN_WRAPPER_OPTS += -ffile-prefix-map=$(BASE_DIR)=buildroot
> +else
> +TOOLCHAIN_WRAPPER_OPTS += -D__FILE__=\"file-path-replaced-by-buildroot-for-reproducibility\"

Maybe __BASE_FILE__ should be handle here too in order to have the save
behaviour as -ffile-prefix-map.
I'm not sure about __builtin_FILE().

Best regards,
Romain

> +endif
>  endif
>  
>  # We create a list like '"-mfoo", "-mbar", "-mbarfoo"' so that each flag is a
>