Re: [dpdk-dev] [PATCH 0/2] Improve function versioning meson support

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 27 Sep 2019 20:49:30 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> Adding support for LTO has exposed some issues with how the functions
> versioning was supported by meson, which was always set to build both
> shared and static libraries.
> 
> For plain C code, so long as the -fPIC compiler flag was passed, the
> output is identical whether or not the code is to be included in a
> static library or a dynamic one. Unfortunately, when using function
> versioning that no longer held as different macros were used for the
> versioned functions depending on which type of build it was. This means
> that any files that use versioning need to be built twice, with
> different defines in each case.
> 
> While the trivial solution here is just to rebuild everything twice,
> that involves a lot of unnecessary work when building DPDK. A better
> option is to identify those files or components which need multiple
> builds and rebuild only those. To do this, we add a new meson.build
> setting for libraries "use_function_versioning" and when that is set, we
> rebuild all source files twice, initially for static library and then
> with -DRTE_BUILD_SHARED_LIB for the shared library.
> 
> If the flag is not set, then the static versioning setting only is used,
> which could lead to the build succeeding but later causing problems. To
> avoid that, we add a new define which must be set when the versioning
> header is included. This addition while solving 1 problem raises 2
> other, more minor problems:
> * what to do with make builds? since make only builds one library type,
>   we can just always define the new value.
> * what about files that include rte_compat.h for the macro for
>   "experimental"? To solve this, we can split compat.h in two, since the
>   versioning macro should be internal only to DPDK (as no public header
>   should expose anything but the latest APIs), while the experimental
>   macros are primarily for public use.
> 
> Bruce Richardson (2):
>   eal: split compat header file
>   build: support building ABI versioned files twice
> 
>  config/common_base                            |  1 +
>  config/rte_config.h                           |  3 ---
>  doc/api/doxy-api-index.md                     |  3 ++-
>  doc/guides/contributing/coding_style.rst      |  7 ++++++
>  doc/guides/contributing/versioning.rst        |  4 ++--
>  lib/librte_distributor/meson.build            |  1 +
>  lib/librte_distributor/rte_distributor.c      |  2 +-
>  lib/librte_distributor/rte_distributor_v20.c  |  2 +-
>  lib/librte_eal/common/Makefile                |  1 +
>  ...rte_compat.h => rte_function_versioning.h} | 23 ++++++-------------
>  lib/librte_lpm/meson.build                    |  1 +
>  lib/librte_lpm/rte_lpm.c                      |  1 +
>  lib/librte_lpm/rte_lpm.h                      |  1 -
>  lib/librte_lpm/rte_lpm6.c                     |  1 +
>  lib/librte_timer/meson.build                  |  1 +
>  lib/librte_timer/rte_timer.c                  |  2 +-
>  lib/meson.build                               | 16 ++++++++++---
>  17 files changed, 41 insertions(+), 29 deletions(-)
>  rename lib/librte_eal/common/include/{rte_compat.h => rte_function_versioning.h} (89%)
> 

Looks fine.
Acked-by: Stephen Hemminger <stephen@networkplumber.org>