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Date: Wed, 9 Oct 2019 15:59:03 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: dev@dpdk.org, Andrzej Ostruszka <amo@semihalf.com>, Thomas Monjalon
<thomas@monjalon.net>, Ray Kinsella <mdr@ashroe.eu>, Neil Horman
<nhorman@tuxdriver.com>
Message-ID: <20191009155903.62c55d42@hermes.lan>
In-Reply-To: <20190927194932.22197-1-bruce.richardson@intel.com>
References: <20190927194932.22197-1-bruce.richardson@intel.com>
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Subject: Re: [dpdk-dev] [PATCH 0/2] Improve function versioning meson support
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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>