[RFC v1 0/1] allow header only libraries

[RFC v1 0/1] allow header only libraries

[Paul Szczepanek]

The current devtools has a check that errors on any
library (except drivers library which is exempted)
that does not export any symbols. I want to create
a header only library. I want to have the check
ignore libraries which have no `global:` section.

Paul Szczepanek (1):
  devtools: allow libraries with no global section

 devtools/check-symbol-maps.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--
2.25.1

[RFC v1 1/1] devtools: allow libraries with no global section

[Paul Szczepanek]

If a library has no global section in the version.map
allow it not to have symbols and not report it as an error.
This happens if a library doesn't export any functions
if they're all inline.

Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
---
 devtools/check-symbol-maps.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/devtools/check-symbol-maps.sh b/devtools/check-symbol-maps.sh
index ba2f892f56..380a251aea 100755
--- a/devtools/check-symbol-maps.sh
+++ b/devtools/check-symbol-maps.sh
@@ -63,7 +63,9 @@ fi
 find_empty_maps ()
 {
     for map in $@ ; do
-        [ $(buildtools/map-list-symbol.sh $map | wc -l) != '0' ] || echo $map
+        # ignore maps that do not have a 'global:' section since they are empty by design
+        [ $(buildtools/map-list-symbol.sh $map | wc -l) != '0' ] ||
+            ! grep -q 'global:' $map || echo $map
     done
 }

--
2.25.1

Re: [RFC v1 1/1] devtools: allow libraries with no global section

[David Marchand]

On Wed, Mar 6, 2024 at 3:36 PM Paul Szczepanek <paul.szczepanek@arm.com> wrote:
>
> If a library has no global section in the version.map
> allow it not to have symbols and not report it as an error.
> This happens if a library doesn't export any functions
> if they're all inline.
>
> Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>

Added Bruce.

Having a library without any actual code compiled is (I think) new in DPDK.

On the other hand, for headers only, there should be no need for a
version.map file at all.

The current meson code expects that every library provides some files
to compile via the sources variable and it expects a version.map file
too.
I wonder if we could skip the whole library generation at the
lib/meson.build level.
Something like:

diff --git a/lib/meson.build b/lib/meson.build
index 179a272932..f0bbab6658 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -222,6 +222,10 @@ foreach l:libraries
     includes += include_directories(l)
     dpdk_includes += include_directories(l)

+    if sources.length() == 0
+        continue
+    endif
+
     if developer_mode and is_windows and use_function_versioning
         message('@0@: Function versioning is not supported by
Windows.'.format(name))
     endif

No version.map, no check to update :-)


-- 
David Marchand

Re: [RFC v1 1/1] devtools: allow libraries with no global section

[Bruce Richardson]

On Wed, Mar 06, 2024 at 05:14:15PM +0100, David Marchand wrote:
> On Wed, Mar 6, 2024 at 3:36 PM Paul Szczepanek <paul.szczepanek@arm.com> wrote:
> >
> > If a library has no global section in the version.map
> > allow it not to have symbols and not report it as an error.
> > This happens if a library doesn't export any functions
> > if they're all inline.
> >
> > Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
> 
> Added Bruce.
> 
> Having a library without any actual code compiled is (I think) new in DPDK.
> 
> On the other hand, for headers only, there should be no need for a
> version.map file at all.
> 
> The current meson code expects that every library provides some files
> to compile via the sources variable and it expects a version.map file
> too.
> I wonder if we could skip the whole library generation at the
> lib/meson.build level.
> Something like:
> 
> diff --git a/lib/meson.build b/lib/meson.build
> index 179a272932..f0bbab6658 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -222,6 +222,10 @@ foreach l:libraries
>      includes += include_directories(l)
>      dpdk_includes += include_directories(l)
> 
> +    if sources.length() == 0
> +        continue
> +    endif
> +
>      if developer_mode and is_windows and use_function_versioning
>          message('@0@: Function versioning is not supported by
> Windows.'.format(name))
>      endif
> 
> No version.map, no check to update :-)
> 
Two thoughts/suggestions here:

* in original meson port we did have support for header only libraries - I
  think for rte_compat.h, but that was done away with when the header was
  just merged into EAL. See [1]
* for a header only lib - if we are prepared to forego being able to
  disable it - the easiest enablement path may be to not add the directory
  to the list of libraries, and just add the header file path to the global
  include path, or perhaps some other library include path. How to make it
  work best may depend on what the library does and what other DPDK libs, if
  any, it depends upon.

[1] http://git.dpdk.org/dpdk/tree/lib/meson.build?h=v18.11&id=0da7f445df445630c794897347ee360d6fe6348b#n72

Re: [RFC v1 1/1] devtools: allow libraries with no global section

[David Marchand]

On Wed, Mar 6, 2024 at 5:40 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
>
> On Wed, Mar 06, 2024 at 05:14:15PM +0100, David Marchand wrote:
> > On Wed, Mar 6, 2024 at 3:36 PM Paul Szczepanek <paul.szczepanek@arm.com> wrote:
> > >
> > > If a library has no global section in the version.map
> > > allow it not to have symbols and not report it as an error.
> > > This happens if a library doesn't export any functions
> > > if they're all inline.
> > >
> > > Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
> >
> > Added Bruce.
> >
> > Having a library without any actual code compiled is (I think) new in DPDK.
> >
> > On the other hand, for headers only, there should be no need for a
> > version.map file at all.
> >
> > The current meson code expects that every library provides some files
> > to compile via the sources variable and it expects a version.map file
> > too.
> > I wonder if we could skip the whole library generation at the
> > lib/meson.build level.
> > Something like:
> >
> > diff --git a/lib/meson.build b/lib/meson.build
> > index 179a272932..f0bbab6658 100644
> > --- a/lib/meson.build
> > +++ b/lib/meson.build
> > @@ -222,6 +222,10 @@ foreach l:libraries
> >      includes += include_directories(l)
> >      dpdk_includes += include_directories(l)
> >
> > +    if sources.length() == 0
> > +        continue
> > +    endif
> > +
> >      if developer_mode and is_windows and use_function_versioning
> >          message('@0@: Function versioning is not supported by
> > Windows.'.format(name))
> >      endif
> >
> > No version.map, no check to update :-)
> >
> Two thoughts/suggestions here:
>
> * in original meson port we did have support for header only libraries - I
>   think for rte_compat.h, but that was done away with when the header was
>   just merged into EAL. See [1]
> * for a header only lib - if we are prepared to forego being able to
>   disable it - the easiest enablement path may be to not add the directory
>   to the list of libraries, and just add the header file path to the global
>   include path, or perhaps some other library include path. How to make it
>   work best may depend on what the library does and what other DPDK libs, if
>   any, it depends upon.

If the goal is to provide those headers as public API, you still need
to call install_headers() somewhere.
And I don't like losing control over disabling about what is shipped.

I prefer [1].


-- 
David Marchand

Re: [RFC v1 1/1] devtools: allow libraries with no global section

[Paul Szczepanek]

On 06/03/2024 16:51, David Marchand wrote:
> On Wed, Mar 6, 2024 at 5:40 PM Bruce Richardson
> <bruce.richardson@intel.com> wrote:
>>
>> On Wed, Mar 06, 2024 at 05:14:15PM +0100, David Marchand wrote:
>>> On Wed, Mar 6, 2024 at 3:36 PM Paul Szczepanek <paul.szczepanek@arm.com> wrote:
>>>>
>>>> If a library has no global section in the version.map
>>>> allow it not to have symbols and not report it as an error.
>>>> This happens if a library doesn't export any functions
>>>> if they're all inline.
>>>>
>>>> Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
>>>
>>> Added Bruce.
>>>
>>> Having a library without any actual code compiled is (I think) new in DPDK.
>>>
>>> On the other hand, for headers only, there should be no need for a
>>> version.map file at all.
>>>
>>> The current meson code expects that every library provides some files
>>> to compile via the sources variable and it expects a version.map file
>>> too.
>>> I wonder if we could skip the whole library generation at the
>>> lib/meson.build level.
>>> Something like:
>>>
>>> diff --git a/lib/meson.build b/lib/meson.build
>>> index 179a272932..f0bbab6658 100644
>>> --- a/lib/meson.build
>>> +++ b/lib/meson.build
>>> @@ -222,6 +222,10 @@ foreach l:libraries
>>>       includes += include_directories(l)
>>>       dpdk_includes += include_directories(l)
>>>
>>> +    if sources.length() == 0
>>> +        continue
>>> +    endif
>>> +
>>>       if developer_mode and is_windows and use_function_versioning
>>>           message('@0@: Function versioning is not supported by
>>> Windows.'.format(name))
>>>       endif
>>>
>>> No version.map, no check to update :-)
>>>
>> Two thoughts/suggestions here:
>>
>> * in original meson port we did have support for header only libraries - I
>>    think for rte_compat.h, but that was done away with when the header was
>>    just merged into EAL. See [1]
>> * for a header only lib - if we are prepared to forego being able to
>>    disable it - the easiest enablement path may be to not add the directory
>>    to the list of libraries, and just add the header file path to the global
>>    include path, or perhaps some other library include path. How to make it
>>    work best may depend on what the library does and what other DPDK libs, if
>>    any, it depends upon.
> 
> If the goal is to provide those headers as public API, you still need
> to call install_headers() somewhere.
> And I don't like losing control over disabling about what is shipped.
> 
> I prefer [1].
> 
> 

I have uploaded a PATCH that follows [1]:
https://patches.dpdk.org/project/dpdk/patch/20240306221709.166722-2-paul.szczepanek@arm.com/
It might be easier to review by applying first as most of the diff is 
just tab indentation change caused by the if.
I have tested it with my header only library and it works.