Re: [dpdk-dev] [PATCH v2 0/10] dpdk: introduce __rte_internal tag

[Thomas Monjalon <thomas@monjalon.net>]

I think it would be good to rebase and send at the beginning of the 19.11 cycle.
Thank you

13/06/2019 16:23, Neil Horman:
> Hey-
>         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
> 
> Summary:
> 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
> 
> 
> Proposal:
> 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.