[dpdk-dev] [RFC PATCH 0/2] introduce __rte_internal tag

Neil Horman nhorman at tuxdriver.com
Sat May 25 20:43:44 CEST 2019

	Based on our recent conversations regarding the use of symbols only
meant for internal dpdk consumption (between dpdk libraries), this is an idea
that I've come up with that I'd like to get some feedback on

1) We have symbols in the DPDK that are meant to be used between DPDK libraries,
but not by applications linking to them
2) We would like to document those symbols in the code, so as to note them
clearly as for being meant for internal use only
3) Linker symbol visibility is a very coarse grained tool, and so there is no
good way in a single library to mark items as being meant for use only by other
DPDK libraries, at least not without some extensive runtime checking

I'm proposing that we introduce the __rte_internal tag.  From a coding
standpoint it works a great deal like the __rte_experimental tag in that it
expempts the tagged symbol from ABI constraints (as the only users should be
represented in the DPDK build environment).  Additionally, the __rte_internal
macro resolves differently based on the definition of the BUILDING_RTE_SDK flag
(working under the assumption that said flag should only ever be set if we are
actually building DPDK libraries which will make use of internal calls).  If the
BUILDING_RTE_SDK flag is set __rte_internal resolves to __attribute__((section
"text.internal)), placing it in a special text section which is then used to
validate that the the symbol appears in the INTERNAL section of the
corresponding library version map).  If BUILDING_RTE_SDK is not set, then
__rte_internal resolves to __attribute__((error("..."))), which causes any
caller of the tagged function to throw an error at compile time, indicating that
the symbol is not available for external use.

This isn't a perfect solution, as applications can still hack around it of
course, but I think it hits some of the high points, restricting symbol access
for any library that prototypes its public and private symbols in the same
header file, excluding the internal symbols from ABI constraints, and clearly
documenting those symbols which we wish to limit to internal usage.

I've included a patch to the dpaa library to demonstrate its usage.  If there is
consensus on this approach, I'll expand and repost the patch, pulling in the
other libraries which have internal-only symbol usage.

Signed-off-by: Neil Horman <nhorman at tuxdriver.com>
CC: Jerin Jacob Kollanukkaran <jerinj at marvell.com>
CC: Bruce Richardson <bruce.richardson at intel.com>
CC: Thomas Monjalon <thomas at monjalon.net>

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