Re: [dpdk-dev] [PATCH v2 01/10] Add __rte_internal tag for functions and version target

[Neil Horman <nhorman@tuxdriver.com>]

On Fri, Apr 17, 2020 at 02:04:30AM +0000, Wang, Haiyue wrote:
> Hi Neil,
> 
> > -----Original Message-----
> > From: dev <dev-bounces@dpdk.org> On Behalf Of Neil Horman
> > Sent: Thursday, June 13, 2019 22:24
> > To: dev@dpdk.org
> > Cc: Neil Horman <nhorman@tuxdriver.com>; Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Richardson,
> > Bruce <bruce.richardson@intel.com>; Thomas Monjalon <thomas@monjalon.net>
> > Subject: [dpdk-dev] [PATCH v2 01/10] Add __rte_internal tag for functions and version target
> > 
> > This tag is meant to be used on function prototypes to identify
> > functions that are only meant to be used by internal DPDK libraries
> > (i.e. libraries that are built while building the SDK itself, as
> > identified by the defining of the BUILDING_RTE_SDK macro).  When that
> > flag is not set, it will resolve to an error function attribute, causing
> > build breakage for any compilation unit attempting to build it
> > 
> > Validate the use of this tag in much the same way we validate
> > __rte_experimental.  By adding an INTERNAL version to library map files,
> > we can exempt internal-only functions from ABI checking, and handle them
> > to ensure that symbols we wish to only be for internal use between dpdk
> > libraries are properly tagged with __rte_experimental
> > 
> > Note this patch updates the check-experimental-syms.sh script, which
> > normally only check the EXPERIMENTAL section to also check the INTERNAL
> > section now.  As such its been renamed to the now more appropriate
> > check-special-syms.sh
> > 
> > Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> > CC: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
> > CC: Bruce Richardson <bruce.richardson@intel.com>
> > CC: Thomas Monjalon <thomas@monjalon.net>
> > ---
> >  ...rimental-syms.sh => check-special-syms.sh} | 24 ++++++++++++++++++-
> >  lib/librte_eal/common/include/rte_compat.h    | 12 ++++++++++
> >  mk/internal/rte.compile-pre.mk                |  6 ++---
> >  mk/target/generic/rte.vars.mk                 |  2 +-
> >  4 files changed, 39 insertions(+), 5 deletions(-)
> >  rename buildtools/{check-experimental-syms.sh => check-special-syms.sh} (53%)
> > 
> ....
> 
> > diff --git a/lib/librte_eal/common/include/rte_compat.h b/lib/librte_eal/common/include/rte_compat.h
> > index 92ff28faf..739e8485c 100644
> > --- a/lib/librte_eal/common/include/rte_compat.h
> > +++ b/lib/librte_eal/common/include/rte_compat.h
> > @@ -89,4 +89,16 @@ __attribute__((section(".text.experimental")))
> > 
> >  #endif
> > 
> > +/*
> > + * __rte_internal tags mark functions as internal only, If specified in public
> > + * header files, this tag will resolve to an error directive, preventing
> > + * external applications from attempting to make calls to functions not meant
> > + * for consumption outside the dpdk library
> > + */
> > +#ifdef BUILDING_RTE_SDK
> > +#define __rte_internal __attribute__((section(".text.internal")))
> > +#else
> > +#define __rte_internal __attribute__((error("This function cannot be used outside of the core DPDK
> > library"), \
> > +	section(".text.internal")))
> > +#endif
> >  #endif /* _RTE_COMPAT_H_ */
> 
> Since struct definition is also a kind of ABI (am I right ? ;-) ), like:
> 
Yes, thats correct, which is why I've advocated for making structs
opaque as part of the abi, but I suppose thats not where we are. :)

> drivers/bus/pci/rte_bus_pci.h
> struct rte_pci_device {
> 	...
> 	struct rte_intr_handle vfio_req_intr_handle;
> 				/**< Handler of VFIO request interrupt */
> } __rte_internal;
> 
> Then will capture the errors anyway by using one of __rte_internal definition.
> 	error: 'section' attribute does not apply to types [-Werror=attributes]
> 	error: 'error' attribute does not apply to types
> 
As it is currently written, the __rte_internal macro is only written to
work on functions.  If you don't want a struct to be part of the ABI, we
would need to either:

a) make a simmilar macro (say __rte_internal_data) which uses a simmilar
gcc attibute to catch external usage.

or

b) just move the strucute definition to a location that isn't exposed as
part of the external ABI

Neil

> > 2.20.1
> 
>