[Buildroot] [PATCH v2] gcc: Build libgcc with BR2_TARGET_OPTIMIZATION flags

[Buildroot] [PATCH v2] gcc: Build libgcc with BR2_TARGET_OPTIMIZATION flags

[Alexey Brodkin]

libgcc gets built very early and what's more it is built not by
"normal" cross gcc later found in "output/host/usr/bin" but by
gcc's own bare-minimal version: output/build/host-gcc-xxx/build/./gcc/xgcc.

Which in the end means BR2_TARGET_OPTIMIZATION is not applied to
cross-compiler via toolchain wrapper.

But given libgcc is an essential target executable we may want it to
be built with the same "optimization" flags as all other libs and binaries.

Technically this is doable with TARGET_ABI which is added to TARGET_CFLAGS
but user cannot [or at least is not supposed to] modify TARGET_ABI as it
is used for tunign for a particular platform.

But still there might be a need to compile everything for tha target with
a special compiler option and this change allows for that.

For eaxmple ARC still doesn't have properly working link-time relaxation
which requires us to compile everything properly from the beginning, otherwise
we may face a situation when huge apps/libs like Qt5WebKit might fail to pass
the final linkage because some symbols might be too far from each other as
by default gcc will try to use shorter relocations. Solution is as simple as
rebuild of everything with "-mlong-calls" so that all the symbols are
compiled with full 32-bit relocations. And now only libgcc causes problems
because it contains quite a few symbols used widely by other binaries like
millicode, some math stuff etc.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---

Changes v1 -> v2:
 * Strip quotes from BR2_TARGET_OPTIMIZATION
   Didn't notice a problem with 1 option in BR2_TARGET_OPTIMIZATION
   but if another one is added libgcc configuration fails because:
   CFLAGS_FOR_TARGET="-xxx "-yyy -zzz"" and thus
   /bin/sh: -zzz: command not found

 package/gcc/gcc.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
index 27fc1e987c..431f534f56 100644
--- a/package/gcc/gcc.mk
+++ b/package/gcc/gcc.mk
@@ -109,7 +109,7 @@ HOST_GCC_COMMON_CONF_OPTS = \
 HOST_GCC_COMMON_CONF_ENV = \
 	MAKEINFO=missing
 
-GCC_COMMON_TARGET_CFLAGS = $(TARGET_CFLAGS)
+GCC_COMMON_TARGET_CFLAGS = $(TARGET_CFLAGS) $(call qstrip,$(BR2_TARGET_OPTIMIZATION))
 GCC_COMMON_TARGET_CXXFLAGS = $(TARGET_CXXFLAGS)
 
 # Propagate options used for target software building to GCC target libs
-- 
2.11.0

[Buildroot] [PATCH v2] gcc: Build libgcc with BR2_TARGET_OPTIMIZATION flags

[Alexey Brodkin]

Hello,

On Thu, 2018-01-18 at 19:56 +0300, Alexey Brodkin wrote:
> libgcc gets built very early and what's more it is built not by
> "normal" cross gcc later found in "output/host/usr/bin" but by
> gcc's own bare-minimal version: output/build/host-gcc-xxx/build/./gcc/xgcc.
> 
> Which in the end means BR2_TARGET_OPTIMIZATION is not applied to
> cross-compiler via toolchain wrapper.
> 
> But given libgcc is an essential target executable we may want it to
> be built with the same "optimization" flags as all other libs and binaries.
> 
> Technically this is doable with TARGET_ABI which is added to TARGET_CFLAGS
> but user cannot [or at least is not supposed to] modify TARGET_ABI as it
> is used for tunign for a particular platform.
> 
> But still there might be a need to compile everything for tha target with
> a special compiler option and this change allows for that.
> 
> For eaxmple ARC still doesn't have properly working link-time relaxation
> which requires us to compile everything properly from the beginning, otherwise
> we may face a situation when huge apps/libs like Qt5WebKit might fail to pass
> the final linkage because some symbols might be too far from each other as
> by default gcc will try to use shorter relocations. Solution is as simple as
> rebuild of everything with "-mlong-calls" so that all the symbols are
> compiled with full 32-bit relocations. And now only libgcc causes problems
> because it contains quite a few symbols used widely by other binaries like
> millicode, some math stuff etc.
> 
> Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> ---
> 
> Changes v1 -> v2:
>  * Strip quotes from BR2_TARGET_OPTIMIZATION
>    Didn't notice a problem with 1 option in BR2_TARGET_OPTIMIZATION
>    but if another one is added libgcc configuration fails because:
>    CFLAGS_FOR_TARGET="-xxx "-yyy -zzz"" and thus
>    /bin/sh: -zzz: command not found

Any comments on this one? If not please consider applying.

-Alexey

[Buildroot] [PATCH v2] gcc: Build libgcc with BR2_TARGET_OPTIMIZATION flags

[Arnout Vandecappelle]

?Hi Alexey,

?Sorry for the extremely late feedback...


On 18/01/2018 16:56, Alexey Brodkin wrote:
> libgcc gets built very early and what's more it is built not by
> "normal" cross gcc later found in "output/host/usr/bin" but by
> gcc's own bare-minimal version: output/build/host-gcc-xxx/build/./gcc/xgcc.
>
> Which in the end means BR2_TARGET_OPTIMIZATION is not applied to
> cross-compiler via toolchain wrapper.

?TBH I don't like this BR2_TARGET_OPTIMIZATION option too much, it's too
unpredictable, but indeed it is sometimes the only way to fix something.

>
> But given libgcc is an essential target executable we may want it to
> be built with the same "optimization" flags as all other libs and binaries.
>
> Technically this is doable with TARGET_ABI which is added to TARGET_CFLAGS
> but user cannot [or at least is not supposed to] modify TARGET_ABI as it
> is used for tunign for a particular platform.
>
> But still there might be a need to compile everything for tha target with
> a special compiler option and this change allows for that.
>
> For eaxmple ARC still doesn't have properly working link-time relaxation
> which requires us to compile everything properly from the beginning, otherwise
> we may face a situation when huge apps/libs like Qt5WebKit might fail to pass
> the final linkage because some symbols might be too far from each other as
> by default gcc will try to use shorter relocations. Solution is as simple as
> rebuild of everything with "-mlong-calls" so that all the symbols are
> compiled with full 32-bit relocations. And now only libgcc causes problems
> because it contains quite a few symbols used widely by other binaries like
> millicode, some math stuff etc.
>
> Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> ---
>
> Changes v1 -> v2:
>  * Strip quotes from BR2_TARGET_OPTIMIZATION
>    Didn't notice a problem with 1 option in BR2_TARGET_OPTIMIZATION
>    but if another one is added libgcc configuration fails because:
>    CFLAGS_FOR_TARGET="-xxx "-yyy -zzz"" and thus
>    /bin/sh: -zzz: command not found
>
>  package/gcc/gcc.mk | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
> index 27fc1e987c..431f534f56 100644
> --- a/package/gcc/gcc.mk
> +++ b/package/gcc/gcc.mk
> @@ -109,7 +109,7 @@ HOST_GCC_COMMON_CONF_OPTS = \
>  HOST_GCC_COMMON_CONF_ENV = \
>  	MAKEINFO=missing
>  
> -GCC_COMMON_TARGET_CFLAGS = $(TARGET_CFLAGS)
> +GCC_COMMON_TARGET_CFLAGS = $(TARGET_CFLAGS) $(call qstrip,$(BR2_TARGET_OPTIMIZATION))
?This looks good to me, but...
>  GCC_COMMON_TARGET_CXXFLAGS = $(TARGET_CXXFLAGS)

... shouldn't it be added here as well, for libstdc++?


?Regards,
?Arnout


>  
>  # Propagate options used for target software building to GCC target libs