Re: [dpdk-dev] [PATCH v8 2/3] build: use Python pmdinfogen

[David Marchand <david.marchand@redhat.com>]

On Mon, Jan 25, 2021 at 11:01 AM Kinsella, Ray <mdr@ashroe.eu> wrote:
>
>
>
> On 25/01/2021 09:25, Kinsella, Ray wrote:
> >
> >
> > On 23/01/2021 11:38, Thomas Monjalon wrote:
> >> 22/01/2021 23:24, Dmitry Kozlyuk:
> >>> On Fri, 22 Jan 2021 21:57:15 +0100, Thomas Monjalon wrote:
> >>>> 22/01/2021 21:31, Dmitry Kozlyuk:
> >>>>> On Wed, 20 Jan 2021 11:24:21 +0100, Thomas Monjalon wrote:
> >>>>>> 20/01/2021 08:23, Dmitry Kozlyuk:
> >>>>>>> On Wed, 20 Jan 2021 01:05:59 +0100, Thomas Monjalon wrote:
> >>>>>>>> This is now the right timeframe to introduce this change
> >>>>>>>> with the new Python module dependency.
> >>>>>>>> Unfortunately, the ABI check is returning an issue:
> >>>>>>>>
> >>>>>>>> 'const char mlx5_common_pci_pmd_info[62]' was changed
> >>>>>>>> to 'const char mlx5_common_pci_pmd_info[60]' at rte_common_mlx5.pmd.c
> >>>>>>>
> >>>>>>> Will investigate and fix ASAP.
> >>>>>
> >>>>> Now that I think of it: strings like this change every time new PCI IDs are
> >>>>> added to a PMD, but AFAIK adding PCI IDs is not considered an ABI breakage,
> >>>>> is it? One example is 28c9a7d7b48e ("net/mlx5: add ConnectX-6 Lx device ID")
> >>>>> added 2020-07-08, i.e. clearly outside of ABI change window.
> >>>>
> >>>> You're right.
> >>>>
> >>>>> "xxx_pmd_info" changes are due to JSON formatting (new is more canonical),
> >>>>> which can be worked around easily, if the above is wrong.
> >>>>
> >>>> If the new format is better, please keep it.
> >>>> What we need is an exception for the pmdinfo symbols
> >>>> in the file devtools/libabigail.abignore.
> >>>> You can probably use a regex for these symbols.
> >>>
> >>> This would allow real breakages to pass ABI check, abidiff doesn't analyze
> >>> variable content and it's not easy to compare. Maybe later a script can be
> >>> added that checks lines with RTE_DEVICE_IN in patches. There are at most 32 of
> >>> 5494 relevant commits between 19.11 and 20.11, though.
> >>>
> >>> To verify there are no meaningful changes I ensured empty diff between
> >>> results of the following command for "main" and the branch:
> >>>
> >>>     find build/drivers -name '*.so' -exec usertools/dpdk-pmdinfo.py
> >>
> >> For now we cannot do such check as part of the ABI checker.
> >> And we cannot merge this patch if the ABI check fails.
> >> I think the only solution is to allow any change in the pmdinfo variables.
> >>
> >
> > So my 2c on this is that this is an acceptable work-around for the v21 (DPDK v20.11) ABI.
> > However we are going to end up carrying this rule in libabigail.ignore indefinitely.
> >
> > Would it make sense to just fix the size of _pmd_info to some reasonably large value -
> > say 128 bytes, to allow us to drop the rule in the DPDK 21.11 v22 release?
> >
> > Ray K
>
>
> Another point is - shouldn't _pmd_info probably live in "INTERNAL" is anycase?

The symbol itself can be hidden from the ABeyes.
It is only a placeholder for the PMD_INFO_STRING= string used by
usertools/dpdk-pmdinfo.py and maybe some other parsing tool.

I guess a static symbol would be enough:

diff --git a/buildtools/pmdinfogen/pmdinfogen.c
b/buildtools/pmdinfogen/pmdinfogen.c
index a68d1ea999..14bf7d9f42 100644
--- a/buildtools/pmdinfogen/pmdinfogen.c
+++ b/buildtools/pmdinfogen/pmdinfogen.c
@@ -393,7 +393,7 @@ static void output_pmd_info_string(struct elf_info
*info, char *outfile)
        drv = info->drivers;

        while (drv) {
-               fprintf(ofd, "const char %s_pmd_info[] __attribute__((used)) = "
+               fprintf(ofd, "static const char %s_pmd_info[]
__attribute__((used)) = "
                        "\"PMD_INFO_STRING= {",
                        drv->name);
                fprintf(ofd, "\\\"name\\\" : \\\"%s\\\", ", drv->name);


We will need an exception for the v21 ABI though.


-- 
David Marchand