[PATCH v2 1/6] Add some gcc/ld optimizations and magic

[Peter Hutterer]

On Sun, Sep 01, 2013 at 05:45:04PM +0200, David Herrmann wrote:
> There are several gcc/ld flags that optimize size and performance without
> requiring explicit code changes. In no particular order, this adds:
>  - gcc -pipe to avoid temporary files and use pipes during compilation
>  - gcc -fno-common avoids putting uninitialized global variables not
>    marked as "extern" into a common section. This catches compilation
>    errors if we didn't mark global variables explicitly as "extern".
>  - gcc -fno-strict-aliasing allows us to use unions for some binary magic.
>    Otherwise, -O2 might assume that two different types never point at the
>    same memory. We currently don't rely on this but it's common practice
>    so avoid any non-obvious runtime errors later.
>  - gcc -ffunction-sections and -fdata-sections put each function and
>    variable into a separate section. This enables ld's --gc-sections to
>    drop any unused sections (sections which aren't referenced from an
>    exported section). This is very useful to avoid putting dead code into
>    DSOs. We can now link any helper function into libevdev and the linker
>    removes all of them if they're unused.
>  - gcc -fstack-protector adds small stack-corruption protectors in
>    functions which have big buffers on the stack (>8bytes). If the
>    stack-protectors are corrupted, the process is aborted. This is highly
>    useful to debug stack-corruption issues which often are nearly
>    impossible to catch without this.
>  - ld --as-needed drops all linked libraries that are not actually
>    required by libevdev. So we can link to whatever we want and the linker
>    will drop everything which is not actually used.
>  - ld -z now, resolve symbols during linking, not during runtime.
>  - ld -z relro, add relocation-read-only section. This allows to put
>    read-only global variables and alike into a read-only section. This is
>    useful for variables that need a relocation and thus cannot be
>    explicitly put into a read-only section. This option tells the linker
>    to mark them read-only after relocations are done. (that's why -z now
>    makes sense in combination with this)
> 
> All of these options are common in other open-source projects, including
> systemd and weston. Don't ask me why they are not marked as default..
> 
> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
> ---

oh, whoops. I thought I had merged that from the previous patchset. sorry.

merged 1/6 and 2/6. I'll skip the others, because I think I dislike the
single makefile approach as much as you like it :)

thanks.

oh, and please run 
  git config --add format.subjectprefix "PATCH `basename $PWD`" 
in your libevdev tree :)

Cheers,
   Peter

>  configure.ac         | 2 +-
>  libevdev/Makefile.am | 9 ++++++++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index 78ab380..a88f7c0 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -42,7 +42,7 @@ AM_CONDITIONAL(BUILD_TESTS, [test "x$HAVE_CHECK" = "xyes"])
>  
>  
>  if test "x$GCC" = "xyes"; then
> -	GCC_CFLAGS="-Wall -Wextra -Wno-unused-parameter -g -Wstrict-prototypes -Wmissing-prototypes -fvisibility=hidden"
> +	GCC_CFLAGS="-Wall -Wextra -Wno-unused-parameter -g -Wstrict-prototypes -Wmissing-prototypes -fvisibility=hidden -pipe -fno-common -fno-strict-aliasing -ffunction-sections -fdata-sections -fstack-protector -fno-strict-aliasing -fdiagnostics-show-option -fno-common"
>  fi
>  AC_SUBST(GCC_CFLAGS)
>  
> diff --git a/libevdev/Makefile.am b/libevdev/Makefile.am
> index 5ebbd42..64adf58 100644
> --- a/libevdev/Makefile.am
> +++ b/libevdev/Makefile.am
> @@ -11,7 +11,14 @@ libevdev_la_SOURCES = \
>                     libevdev-uinput-int.h \
>                     libevdev.c
>  
> -libevdev_la_LDFLAGS = -version-info $(LIBEVDEV_LT_VERSION) -export-symbols-regex '^libevdev_' $(GCOV_LDFLAGS)
> +libevdev_la_LDFLAGS = \
> +	-version-info $(LIBEVDEV_LT_VERSION) \
> +	-export-symbols-regex '^libevdev_' \
> +	$(GCOV_LDFLAGS) \
> +	-Wl,--as-needed \
> +	-Wl,--gc-sections \
> +	-Wl,-z,relro \
> +	-Wl,-z,now
>  
>  libevdevincludedir = $(includedir)/libevdev-1.0/libevdev
>  libevdevinclude_HEADERS = libevdev.h libevdev-uinput.h
> -- 
> 1.8.4
>