[PATCH] build: fix linker warnings about undefined symbols

[PATCH] build: fix linker warnings about undefined symbols

[Bruce Richardson]

The default behaviour of "ld.lld" has changed, so it now prints out
warnings about entries in the version.map file which don't exist in
the current build. Since we use our version.map file simply to filter
out the functions we don't want made public, we include in it all
functions across all OS's and builds that we want public if present.
This causes these ld warnings to be emitted, e.g. on BSD, which is
missing functionality found on Linux. For example:

* hpet functions in EAL
* regexdev enqueue and dequeue burst
* eventdev event_timer functions

Easiest solution, without major rework of how we use our version.map
files, and without dynamically generating them per-build, is to pass
the --undefined-version flag to the linker, to restore the old
behaviour.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---
 config/meson.build | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/config/meson.build b/config/meson.build
index 73737921c3..cfc29ba757 100644
--- a/config/meson.build
+++ b/config/meson.build
@@ -187,6 +187,9 @@ dpdk_conf.set('RTE_ARCH_32', cc.sizeof('void *') == 4)
 
 if not is_windows
     add_project_link_arguments('-Wl,--no-as-needed', language: 'c')
+    if cc.has_link_argument('-Wl,--undefined-version')
+        add_project_link_arguments('-Wl,--undefined-version', language: 'c')
+    endif
 endif
 
 # use pthreads if available for the platform
-- 
2.40.1

Re: [PATCH] build: fix linker warnings about undefined symbols

[Tyler Retzlaff]

On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> The default behaviour of "ld.lld" has changed, so it now prints out
> warnings about entries in the version.map file which don't exist in
> the current build. Since we use our version.map file simply to filter
> out the functions we don't want made public, we include in it all
> functions across all OS's and builds that we want public if present.
> This causes these ld warnings to be emitted, e.g. on BSD, which is
> missing functionality found on Linux. For example:
> 
> * hpet functions in EAL
> * regexdev enqueue and dequeue burst
> * eventdev event_timer functions
> 
> Easiest solution, without major rework of how we use our version.map
> files, and without dynamically generating them per-build, is to pass
> the --undefined-version flag to the linker, to restore the old
> behaviour.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---

Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>

i don't know if has ever been discussed but a way to achieve a similar
outcome would be to introduce a visibility macro allowing the data and
function symbols to be explicitly made visible while making the build
default hidden.

https://gcc.gnu.org/wiki/Visibility

on windows symbols are hidden by default (opposite of gnu toolchain) and
allowing the symbols that are intended to be public be annotated in code
with a macro instead of a separate map/def file would arguably appear
more consistent.  additionally, the current process of converting a map
file to a def file for windows has limitations with respect to things
like marking the type of symbol being exported.

ty

RE: [PATCH] build: fix linker warnings about undefined symbols

[Morten Brørup]

> From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> Sent: Wednesday, 10 January 2024 17.58
> 
> On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> > The default behaviour of "ld.lld" has changed, so it now prints out
> > warnings about entries in the version.map file which don't exist in
> > the current build. Since we use our version.map file simply to filter
> > out the functions we don't want made public, we include in it all
> > functions across all OS's and builds that we want public if present.
> > This causes these ld warnings to be emitted, e.g. on BSD, which is
> > missing functionality found on Linux. For example:
> >
> > * hpet functions in EAL
> > * regexdev enqueue and dequeue burst
> > * eventdev event_timer functions
> >
> > Easiest solution, without major rework of how we use our version.map
> > files, and without dynamically generating them per-build, is to pass
> > the --undefined-version flag to the linker, to restore the old
> > behaviour.
> >
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> 
> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> 
> i don't know if has ever been discussed but a way to achieve a similar
> outcome would be to introduce a visibility macro allowing the data and
> function symbols to be explicitly made visible while making the build
> default hidden.
> 
> https://gcc.gnu.org/wiki/Visibility

This looks interesting!
Declaring a function "public" directly in its header seems much simpler to manage than having to add it to the version.map file too.

I wonder if function versioning is still supported if using this instead of version.map files?
Of if there are other relevant reasons for continuing to use the version.map files instead of this?

> 
> on windows symbols are hidden by default (opposite of gnu toolchain)
> and
> allowing the symbols that are intended to be public be annotated in
> code
> with a macro instead of a separate map/def file would arguably appear
> more consistent.  additionally, the current process of converting a map
> file to a def file for windows has limitations with respect to things
> like marking the type of symbol being exported.
> 
> ty

Re: [PATCH] build: fix linker warnings about undefined symbols

[Bruce Richardson]

On Thu, Jan 11, 2024 at 10:38:05AM +0100, Morten Brørup wrote:
> > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> > Sent: Wednesday, 10 January 2024 17.58
> > 
> > On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> > > The default behaviour of "ld.lld" has changed, so it now prints out
> > > warnings about entries in the version.map file which don't exist in
> > > the current build. Since we use our version.map file simply to filter
> > > out the functions we don't want made public, we include in it all
> > > functions across all OS's and builds that we want public if present.
> > > This causes these ld warnings to be emitted, e.g. on BSD, which is
> > > missing functionality found on Linux. For example:
> > >
> > > * hpet functions in EAL
> > > * regexdev enqueue and dequeue burst
> > > * eventdev event_timer functions
> > >
> > > Easiest solution, without major rework of how we use our version.map
> > > files, and without dynamically generating them per-build, is to pass
> > > the --undefined-version flag to the linker, to restore the old
> > > behaviour.
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > 
> > Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > 
> > i don't know if has ever been discussed but a way to achieve a similar
> > outcome would be to introduce a visibility macro allowing the data and
> > function symbols to be explicitly made visible while making the build
> > default hidden.
> > 
> > https://gcc.gnu.org/wiki/Visibility
> 
> This looks interesting!
> Declaring a function "public" directly in its header seems much simpler to manage than having to add it to the version.map file too.
> 
> I wonder if function versioning is still supported if using this instead of version.map files?
> Of if there are other relevant reasons for continuing to use the version.map files instead of this?
> 

I don't see in that wiki page and details of how to mark symbols with
different ABI versions. For example, as well as listing what functions are
public, our version.map files also identify the ABI version (e.g. DPDK_24)
they belong to, or whether they are experimental or internal. Having them
all in the version file also makes it easy to see how many experimental
functions we have in each component.

/Bruce

Re: [PATCH] build: fix linker warnings about undefined symbols

[Tyler Retzlaff]

On Thu, Jan 11, 2024 at 09:48:33AM +0000, Bruce Richardson wrote:
> On Thu, Jan 11, 2024 at 10:38:05AM +0100, Morten Brørup wrote:
> > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> > > Sent: Wednesday, 10 January 2024 17.58
> > > 
> > > On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> > > > The default behaviour of "ld.lld" has changed, so it now prints out
> > > > warnings about entries in the version.map file which don't exist in
> > > > the current build. Since we use our version.map file simply to filter
> > > > out the functions we don't want made public, we include in it all
> > > > functions across all OS's and builds that we want public if present.
> > > > This causes these ld warnings to be emitted, e.g. on BSD, which is
> > > > missing functionality found on Linux. For example:
> > > >
> > > > * hpet functions in EAL
> > > > * regexdev enqueue and dequeue burst
> > > > * eventdev event_timer functions
> > > >
> > > > Easiest solution, without major rework of how we use our version.map
> > > > files, and without dynamically generating them per-build, is to pass
> > > > the --undefined-version flag to the linker, to restore the old
> > > > behaviour.
> > > >
> > > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > > ---
> > > 
> > > Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > 
> > > i don't know if has ever been discussed but a way to achieve a similar
> > > outcome would be to introduce a visibility macro allowing the data and
> > > function symbols to be explicitly made visible while making the build
> > > default hidden.
> > > 
> > > https://gcc.gnu.org/wiki/Visibility
> > 
> > This looks interesting!
> > Declaring a function "public" directly in its header seems much simpler to manage than having to add it to the version.map file too.
> > 
> > I wonder if function versioning is still supported if using this instead of version.map files?
> > Of if there are other relevant reasons for continuing to use the version.map files instead of this?
> > 
> 
> I don't see in that wiki page and details of how to mark symbols with
> different ABI versions. For example, as well as listing what functions are
> public, our version.map files also identify the ABI version (e.g. DPDK_24)
> they belong to, or whether they are experimental or internal. Having them
> all in the version file also makes it easy to see how many experimental
> functions we have in each component.

you can use symver in combination with visibility default

https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

anyway just food for thought, it would get me out of having to hack &
enhance the .def from .map generation and unfortunately even with that
there are going to be cases where i still have to annotate the actual
symbol export in code (for windows).

just thought a more unified approach for all might appeal.

ty

> 
> /Bruce

RE: [PATCH] build: fix linker warnings about undefined symbols

[Morten Brørup]

> From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> Sent: Friday, 12 January 2024 21.11
> 
> On Thu, Jan 11, 2024 at 09:48:33AM +0000, Bruce Richardson wrote:
> > On Thu, Jan 11, 2024 at 10:38:05AM +0100, Morten Brørup wrote:
> > > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> > > > Sent: Wednesday, 10 January 2024 17.58
> > > >
> > > > On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> > > > > The default behaviour of "ld.lld" has changed, so it now prints
> out
> > > > > warnings about entries in the version.map file which don't
> exist in
> > > > > the current build. Since we use our version.map file simply to
> filter
> > > > > out the functions we don't want made public, we include in it
> all
> > > > > functions across all OS's and builds that we want public if
> present.
> > > > > This causes these ld warnings to be emitted, e.g. on BSD, which
> is
> > > > > missing functionality found on Linux. For example:
> > > > >
> > > > > * hpet functions in EAL
> > > > > * regexdev enqueue and dequeue burst
> > > > > * eventdev event_timer functions
> > > > >
> > > > > Easiest solution, without major rework of how we use our
> version.map
> > > > > files, and without dynamically generating them per-build, is to
> pass
> > > > > the --undefined-version flag to the linker, to restore the old
> > > > > behaviour.
> > > > >
> > > > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > > > ---
> > > >
> > > > Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > >
> > > > i don't know if has ever been discussed but a way to achieve a
> similar
> > > > outcome would be to introduce a visibility macro allowing the
> data and
> > > > function symbols to be explicitly made visible while making the
> build
> > > > default hidden.
> > > >
> > > > https://gcc.gnu.org/wiki/Visibility
> > >
> > > This looks interesting!
> > > Declaring a function "public" directly in its header seems much
> simpler to manage than having to add it to the version.map file too.
> > >
> > > I wonder if function versioning is still supported if using this
> instead of version.map files?
> > > Of if there are other relevant reasons for continuing to use the
> version.map files instead of this?
> > >
> >
> > I don't see in that wiki page and details of how to mark symbols with
> > different ABI versions. For example, as well as listing what
> functions are
> > public, our version.map files also identify the ABI version (e.g.
> DPDK_24)
> > they belong to, or whether they are experimental or internal. Having
> them
> > all in the version file also makes it easy to see how many
> experimental
> > functions we have in each component.
> 
> you can use symver in combination with visibility default
> 
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
> 
> anyway just food for thought, it would get me out of having to hack &
> enhance the .def from .map generation and unfortunately even with that
> there are going to be cases where i still have to annotate the actual
> symbol export in code (for windows).
> 
> just thought a more unified approach for all might appeal.

Assuming that we truly want DPDK to support Windows, a more unified approach is a reasonable ask.

If we can eliminate the technical obstacles, we should pursue it.

We may have to sacrifice some "nice to have" advantages of the version.map files along the way, such as having easy access to the list of experimental functions in the version.map file.

Re: [PATCH] build: fix linker warnings about undefined symbols

[Stephen Hemminger]

On Fri, 12 Jan 2024 21:49:13 +0100
Morten Brørup <mb@smartsharesystems.com> wrote:

> > you can use symver in combination with visibility default
> > 
> > https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
> > 
> > anyway just food for thought, it would get me out of having to hack &
> > enhance the .def from .map generation and unfortunately even with that
> > there are going to be cases where i still have to annotate the actual
> > symbol export in code (for windows).
> > 
> > just thought a more unified approach for all might appeal.  
> 
> Assuming that we truly want DPDK to support Windows, a more unified approach is a reasonable ask.
> 
> If we can eliminate the technical obstacles, we should pursue it.
> 
> We may have to sacrifice some "nice to have" advantages of the version.map files along the way, such as having easy access to the list of experimental functions in the version.map file.

Ideally __rte_experimental macro would do the right thing to make it publicly visible in the right section.

Re: [PATCH] build: fix linker warnings about undefined symbols

[David Marchand]

On Fri, Jan 12, 2024 at 9:49 PM Morten Brørup <mb@smartsharesystems.com> wrote:
> > you can use symver in combination with visibility default
> >
> > https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
> >
> > anyway just food for thought, it would get me out of having to hack &
> > enhance the .def from .map generation and unfortunately even with that
> > there are going to be cases where i still have to annotate the actual
> > symbol export in code (for windows).

Versioning a symbol means you are exporting it, is it not that simple?
So I don't see the need for annotating about symbol visibility.


> >
> > just thought a more unified approach for all might appeal.
>
> Assuming that we truly want DPDK to support Windows, a more unified approach is a reasonable ask.
>
> If we can eliminate the technical obstacles, we should pursue it.

IIUC, we still need a "default" version script, as the linker needs
one to declare version nodes, and so we have a catch all for
unversioned symbols.

$ cat symver.c
__attribute__ ((__symver__ ("api1@DPDK_23")))
int old_api1(void) { return 0; }

__attribute__ ((__symver__ ("api1@@DPDK_24")))
int api1(void) { return 0; }

__attribute__ ((__symver__ ("api2@@DPDK_24")))
int api2(void) { return 0; }

int api3(void) { return 0; }

$ cat symver.map
DPDK_23 { };
DPDK_24 { };
EXPERIMENTAL { };
INTERNAL {
    local: *;
};

$ gcc -o symver.o -fPIC -Wall -Werror -c symver.c && gcc -o
libsymver.so -shared -fPIC -Wl,--version-script symver.map symver.o &&
readelf -s libsymver.so | grep api
     5: 0000000000001104    11 FUNC    GLOBAL DEFAULT   13 api1@@DPDK_24
     7: 00000000000010f9    11 FUNC    GLOBAL DEFAULT   13 api1@DPDK_23
     9: 000000000000110f    11 FUNC    GLOBAL DEFAULT   13 api2@@DPDK_24
    13: 00000000000010f9    11 FUNC    LOCAL  DEFAULT   13 old_api1
    15: 0000000000001104    11 FUNC    LOCAL  DEFAULT   13 api1
    16: 000000000000111a    11 FUNC    LOCAL  DEFAULT   13 api3
    19: 000000000000110f    11 FUNC    LOCAL  DEFAULT   13 api2
    24: 0000000000001104    11 FUNC    GLOBAL DEFAULT   13 api1@@DPDK_24
    29: 00000000000010f9    11 FUNC    GLOBAL DEFAULT   13 api1@DPDK_23
    31: 000000000000110f    11 FUNC    GLOBAL DEFAULT   13 api2@@DPDK_24


>
> We may have to sacrifice some "nice to have" advantages of the version.map files along the way, such as having easy access to the list of experimental functions in the version.map file.

Developers lose the single location for versioning information, but we
already have some scripts to help list symbols from a given version.
We may have to enhance them.
But I don't think we would lose features.

The devil is probably in the details, though :-).


-- 
David Marchand

Re: [PATCH] build: fix linker warnings about undefined symbols

[Tyler Retzlaff]

On Mon, Jan 15, 2024 at 09:56:45AM +0100, David Marchand wrote:
> On Fri, Jan 12, 2024 at 9:49 PM Morten Brørup <mb@smartsharesystems.com> wrote:
> > > you can use symver in combination with visibility default
> > >
> > > https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
> > >
> > > anyway just food for thought, it would get me out of having to hack &
> > > enhance the .def from .map generation and unfortunately even with that
> > > there are going to be cases where i still have to annotate the actual
> > > symbol export in code (for windows).
> 
> Versioning a symbol means you are exporting it, is it not that simple?
> So I don't see the need for annotating about symbol visibility.
> 
> 
> > >
> > > just thought a more unified approach for all might appeal.
> >
> > Assuming that we truly want DPDK to support Windows, a more unified approach is a reasonable ask.
> >
> > If we can eliminate the technical obstacles, we should pursue it.
> 
> IIUC, we still need a "default" version script, as the linker needs
> one to declare version nodes, and so we have a catch all for
> unversioned symbols.
> 
> $ cat symver.c
> __attribute__ ((__symver__ ("api1@DPDK_23")))
> int old_api1(void) { return 0; }
> 
> __attribute__ ((__symver__ ("api1@@DPDK_24")))
> int api1(void) { return 0; }
> 
> __attribute__ ((__symver__ ("api2@@DPDK_24")))
> int api2(void) { return 0; }
> 
> int api3(void) { return 0; }
> 
> $ cat symver.map
> DPDK_23 { };
> DPDK_24 { };
> EXPERIMENTAL { };
> INTERNAL {
>     local: *;
> };
> 
> $ gcc -o symver.o -fPIC -Wall -Werror -c symver.c && gcc -o
> libsymver.so -shared -fPIC -Wl,--version-script symver.map symver.o &&
> readelf -s libsymver.so | grep api
>      5: 0000000000001104    11 FUNC    GLOBAL DEFAULT   13 api1@@DPDK_24
>      7: 00000000000010f9    11 FUNC    GLOBAL DEFAULT   13 api1@DPDK_23
>      9: 000000000000110f    11 FUNC    GLOBAL DEFAULT   13 api2@@DPDK_24
>     13: 00000000000010f9    11 FUNC    LOCAL  DEFAULT   13 old_api1
>     15: 0000000000001104    11 FUNC    LOCAL  DEFAULT   13 api1
>     16: 000000000000111a    11 FUNC    LOCAL  DEFAULT   13 api3
>     19: 000000000000110f    11 FUNC    LOCAL  DEFAULT   13 api2
>     24: 0000000000001104    11 FUNC    GLOBAL DEFAULT   13 api1@@DPDK_24
>     29: 00000000000010f9    11 FUNC    GLOBAL DEFAULT   13 api1@DPDK_23
>     31: 000000000000110f    11 FUNC    GLOBAL DEFAULT   13 api2@@DPDK_24
> 
> 
> >
> > We may have to sacrifice some "nice to have" advantages of the version.map files along the way, such as having easy access to the list of experimental functions in the version.map file.
> 
> Developers lose the single location for versioning information, but we
> already have some scripts to help list symbols from a given version.
> We may have to enhance them.
> But I don't think we would lose features.
> 
> The devil is probably in the details, though :-).

so my mention of using visibility was more about changes that need to be
made to handle windows dso/dll and wondering if a macro based approach
would result in something unified for both windows and unix targets.

today as you know we use a .map as an authoritative source for the
exported symbols and translate the contents of the .map to a .def for
the windows linker.

going forward to fix dso/dll on windows i'll need to do 2 things.

* exclusive export of a subset of symbols for windows only
* annotation of certain data symbols with type information

since the .map is authoritative i can't just plant either of the above
into the .map in order to pass it through to the generated .def file.

* we could maintain a mostly duplicated copy of .def and stop generating
  it allowing the above additions for windows only.

* we could go hybrid approach where some of the windows symbols are
  listed in the .map and some of them are macros in the code.

* we could move to some single authoritative source that isn't just
  defacto default of a toolchain and generate both .map and .def

* we could move to visibility and symbol marking with macros in the code
  for all symbols, of course the expansion is still conditional but
  you could reasonably grep the tree to generate a full set of exported
  names.

if the suggestion to use visibility and macros for both isn't popular
i'm most likely to look at the hybrid approach since i don't have a lot
of interest in trying to mangle things into comments of the .map for
.def generation and don't think inventing a new common/authoritative
format and maintaining a .map and .def generator is interesting.

i'm open to input, so just fishing for others who have stronger
opinions.

ty

> 
> -- 
> David Marchand

Re: [PATCH] build: fix linker warnings about undefined symbols

[Thomas Monjalon]

10/01/2024 17:58, Tyler Retzlaff:
> On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> > The default behaviour of "ld.lld" has changed, so it now prints out
> > warnings about entries in the version.map file which don't exist in
> > the current build. Since we use our version.map file simply to filter
> > out the functions we don't want made public, we include in it all
> > functions across all OS's and builds that we want public if present.
> > This causes these ld warnings to be emitted, e.g. on BSD, which is
> > missing functionality found on Linux. For example:
> > 
> > * hpet functions in EAL
> > * regexdev enqueue and dequeue burst
> > * eventdev event_timer functions
> > 
> > Easiest solution, without major rework of how we use our version.map
> > files, and without dynamically generating them per-build, is to pass
> > the --undefined-version flag to the linker, to restore the old
> > behaviour.
> > 
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>

+Cc stable

Applied as easy solution for this linker.

The discussion about Windows linker and use of macros
deserve to continue, maybe in a new dedicated thread?

> i don't know if has ever been discussed but a way to achieve a similar
> outcome would be to introduce a visibility macro allowing the data and
> function symbols to be explicitly made visible while making the build
> default hidden.
> 
> https://gcc.gnu.org/wiki/Visibility
> 
> on windows symbols are hidden by default (opposite of gnu toolchain) and
> allowing the symbols that are intended to be public be annotated in code
> with a macro instead of a separate map/def file would arguably appear
> more consistent.  additionally, the current process of converting a map
> file to a def file for windows has limitations with respect to things
> like marking the type of symbol being exported.

Re: [PATCH] build: fix linker warnings about undefined symbols

[Tyler Retzlaff]

On Sun, Feb 18, 2024 at 06:38:22PM +0100, Thomas Monjalon wrote:
> 10/01/2024 17:58, Tyler Retzlaff:
> > On Wed, Jan 10, 2024 at 03:01:03PM +0000, Bruce Richardson wrote:
> > > The default behaviour of "ld.lld" has changed, so it now prints out
> > > warnings about entries in the version.map file which don't exist in
> > > the current build. Since we use our version.map file simply to filter
> > > out the functions we don't want made public, we include in it all
> > > functions across all OS's and builds that we want public if present.
> > > This causes these ld warnings to be emitted, e.g. on BSD, which is
> > > missing functionality found on Linux. For example:
> > > 
> > > * hpet functions in EAL
> > > * regexdev enqueue and dequeue burst
> > > * eventdev event_timer functions
> > > 
> > > Easiest solution, without major rework of how we use our version.map
> > > files, and without dynamically generating them per-build, is to pass
> > > the --undefined-version flag to the linker, to restore the old
> > > behaviour.
> > > 
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > 
> > Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> 
> +Cc stable
> 
> Applied as easy solution for this linker.
> 
> The discussion about Windows linker and use of macros
> deserve to continue, maybe in a new dedicated thread?

yes, i will start a new discussion on the topic after clearing other
windows / msvc changes as soon as i have time.

thanks!

> 
> > i don't know if has ever been discussed but a way to achieve a similar
> > outcome would be to introduce a visibility macro allowing the data and
> > function symbols to be explicitly made visible while making the build
> > default hidden.
> > 
> > https://gcc.gnu.org/wiki/Visibility
> > 
> > on windows symbols are hidden by default (opposite of gnu toolchain) and
> > allowing the symbols that are intended to be public be annotated in code
> > with a macro instead of a separate map/def file would arguably appear
> > more consistent.  additionally, the current process of converting a map
> > file to a def file for windows has limitations with respect to things
> > like marking the type of symbol being exported.
> 
>