Re: [PATCH v4 0/4] allow pmdinfo to be inserted and parsed using MSVC

[Andre Muezerie <andremue@linux.microsoft.com>]

On Wed, Jun 04, 2025 at 02:03:56PM +0200, David Marchand wrote:
> On Tue, Jun 3, 2025 at 3:01 AM Andre Muezerie
> <andremue@linux.microsoft.com> wrote:
> >
> > On Wed, Apr 16, 2025 at 02:44:54PM -0700, Andre Muezerie wrote:
> > > DPDK uses GCC attribute "used" through macro __rte_used to indicate
> > > that a variable not referenced in the code should be assumed being
> > > used and therefore not be optimized away. This technique is used to embed
> > > information in the binaries, by having crafted information stored in
> > > them.
> > >
> > > MSVC offers similar functionality, but it differs significantly: MSVC
> > > requires a pragma to be used to send a command to the linker telling it
> > > explicitly the name of the symbol that should be included (even if not
> > > referenced). As a side-effect, variables called out to be included cannot
> > > be static, otherwise their symbols are not "seen" by the linker. This
> > > restriction requires some DPDK code to be refactored.
> > >
> > > Macro RTE_INCLUDE is used in this patch to ensure these special variables
> > > make it to the final binaries.
> > >
> > > The elimination of "static" for some of these variables caused name
> > > clashes when __COUNTER__ predefined macro was used. As a workaround,
> > > predefined macro __LINE__ was used instead. However, when __COUNTER__
> > > was used directly from a header file, __LINE__ had to be used from the
> > > .c files, otherwise it would also not result in a unique symbol. This
> > > required a parameter to be added to some macros so that the __LINE__
> > > could be passed from the .c file to the macro defined in the header
> > > (which was originally using __COUNTER__).
> > >
> > > With this patchset commands like the one below provide the same JSON
> > > output as would be obtained on Linux.
> > >
> > > python usertools\dpdk-pmdinfo.py build\app\dpdk-testpmd.exe
> > >
> > > v4:
> > >  - limited the use of __LINE__ to the header files, reducing number of
> > >    changes made in previous versions of this patchset.
> 
> Open question, since the submission of this series, __rte_used is used
> in the new symbol export macros.
> It seems those macros are not affected by the problem you described
> (and fixed with RTE_INCLUDE).
> Is it because the symbols are explicitly listed as exported?
> 

Correct. When using MSVC, "__rte_used" is stripped away by the preprocessor
and therefore has no effect. All required symbols need to be explicitly
listed as exported, otherwise the linker will complain about symbols not
found.

> 
> -- 
> David Marchand