Re: [dpdk-dev] [PATCH v2 2/2] build: support building ABI versioned files twice

[Andrzej Ostruszka <amo@semihalf.com>]

Thanks Bruce for the patch.  I like the idea of splitting versioning out
of rte_compat.h, but I have some comments.

On 9/27/19 10:59 PM, Bruce Richardson wrote:
[...]
> --- a/config/common_base
> +++ b/config/common_base
> @@ -111,6 +111,7 @@ CONFIG_RTE_MAX_VFIO_CONTAINERS=64
>  CONFIG_RTE_MALLOC_DEBUG=n
>  CONFIG_RTE_EAL_NUMA_AWARE_HUGEPAGES=n
>  CONFIG_RTE_USE_LIBBSD=n
> +CONFIG_RTE_USE_FUNCTION_VERSIONING=y

I'm not fond of this config option - it is not really an option to be
changed by the user.  I would prefer to just add flag to CFLAGS in
mk/target/generic/rte.vars.mk.

>  #
>  # Recognize/ignore the AVX/AVX512 CPU flags for performance/power testing.
> diff --git a/config/rte_config.h b/config/rte_config.h
> index 0bbbe274f..b63a2fdea 100644
> --- a/config/rte_config.h
> +++ b/config/rte_config.h
> @@ -31,9 +31,6 @@
>  
>  /****** library defines ********/
>  
> -/* compat defines */
> -#define RTE_BUILD_SHARED_LIB
> -

So now everything builds "as static lib" (but with "-fPIC") apart from
those libraries that use symbol versioning.  I'm OK with that however
I'd like to note that code might be using RTE_BUILD_SHARED_LIB and do
different things e.g. app/test-bbdev/test_bbdev_perf.c.  I know that was
already the case - just wanted to say that aloud to make sure we are all
aware of this :).

> diff --git a/doc/guides/contributing/coding_style.rst b/doc/guides/contributing/coding_style.rst
> index 449b33494..e95a1a2be 100644
> --- a/doc/guides/contributing/coding_style.rst
> +++ b/doc/guides/contributing/coding_style.rst
> @@ -948,6 +948,13 @@ reason
>  	built. For missing dependencies this should be of the form
>  	``'missing dependency, "libname"'``.
>  
> +use_function_versioning
> +	**Default Value = false**.
> +	Specifies if the library in question has ABI versioned functions. If it
> +	has, this value should be set to ensure that the C files are compiled
> +	twice with suitable parameters for each of shared or static library
> +	builds.
> +

Maybe a different name for this option?  In general an "ideal
theoretical" solution would be for build system to figure out on its own
that separate build is necessary automatically - but that might incur
some performance penalty (additional grep'ing of sources or so).  So I'm
fine with this option however I'd like to rename it to actually indicate
what it's effect is.  Like 'separate_build' or 'split_build' or
'rebuild_objects' or ...

The intention of using of versioned symbols is already indicated by
inclusion of the relevant header.

> diff --git a/lib/librte_eal/common/include/rte_function_versioning.h b/lib/librte_eal/common/include/rte_function_versioning.h
> index ce963d4b1..55e88ffae 100644
> --- a/lib/librte_eal/common/include/rte_function_versioning.h
> +++ b/lib/librte_eal/common/include/rte_function_versioning.h
> @@ -7,6 +7,10 @@
>  #define _RTE_FUNCTION_VERSIONING_H_
>  #include <rte_common.h>
>  
> +#ifndef RTE_USE_FUNCTION_VERSIONING
> +#error Use of function versioning disabled, is "use_function_versioning=true" in meson.build?
> +#endif

If you accept above suggestion then change this message to something
like: "Function versioning requires 'separate_build=true' in meson.build"

BTW it turned out that this need for separate build for versioned
symbols is a result of long standing gcc bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48200

I'll test this with clang and if this will work then maybe we could
guard this #if with another check for 'gcc'.

Best regards
Andrzej

Tested-by: Andrzej Ostruszka <amo@semihalf.com>