ipp-usb ftbfs with lto

[Matthias Klose]

ipp-usb ftbfs with lto, apparently not seen on Fedora builds.

github.com/OpenPrinting/ipp-usb
# github.com/OpenPrinting/ipp-usb
../../../../tmp/go-build3834344537/b001/cgo-generated-wrappers:1:13: error: function ‘avahiClientCallback’ redeclared as variable
../../../../tmp/go-build3834344537/b001/_cgo_export.c:24:6: note: previously declared here
   24 | void avahiClientCallback(AvahiClient* client, AvahiClientState state, void* _)
      | ^
../../../../tmp/go-build3834344537/b001/cgo-generated-wrappers:4:13: error: function ‘avahiEntryGroupCallback’ redeclared as variable
../../../../tmp/go-build3834344537/b001/_cgo_export.c:46:6: note: previously declared here
   46 | void avahiEntryGroupCallback(AvahiEntryGroup* egroup, AvahiEntryGroupState state, void* _)
      | ^
../../../../tmp/go-build3834344537/b001/cgo-generated-wrappers:7:13: error: function ‘libusbHotplugCallback’ redeclared as variable
../../../../tmp/go-build3834344537/b001/_cgo_export.c:68:5: note: previously declared here
   68 | int libusbHotplugCallback(libusb_context* ctx, libusb_device* dev, libusb_hotplug_event event, void* p)
      | ^
../../../../tmp/go-build3834344537/b001/_cgo_export.c:21:13: error: variable ‘_cgoexp_73d50ba221cf_avahiClientCallback’ redeclared as function
   21 | extern void _cgoexp_73d50ba221cf_avahiClientCallback(void *);
      | ^
../../../../tmp/go-build3834344537/b001/cgo-generated-wrappers:10:5: note: previously declared here
../../../../tmp/go-build3834344537/b001/_cgo_export.c:43:13: error: variable ‘_cgoexp_73d50ba221cf_avahiEntryGroupCallback’ redeclared as function
   43 | extern void _cgoexp_73d50ba221cf_avahiEntryGroupCallback(void *);
      | ^
../../../../tmp/go-build3834344537/b001/cgo-generated-wrappers:11:5: note: previously declared here
../../../../tmp/go-build3834344537/b001/_cgo_export.c:65:13: error: variable ‘_cgoexp_73d50ba221cf_libusbHotplugCallback’ redeclared as function
   65 | extern void _cgoexp_73d50ba221cf_libusbHotplugCallback(void *);
      | ^
../../../../tmp/go-build3834344537/b001/cgo-generated-wrappers:12:5: note: previously declared here
lto1: fatal error: errors during merging of translation units
compilation terminated.
lto-wrapper: fatal error: /usr/bin/gcc returned 1 exit status
compilation terminated.
/usr/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status

[Matthias Klose (doko)]

https://go-review.googlesource.com/c/go/+/322614/

[Till Kamppeter (till-kamppeter)]

@Alexander, could you have a look what is happening here?

[Alexander Pevzner (pzz)]

It looks like Go compiler bug (or, more strictly, cgo bug; cgo is a tool that comes with Go compiler and allows direct calling of C functions from Go)

https://github.com/golang/go/issues/43830

The solution could be to build without LTO. In general, LTO should not make a lot of sense for Go programs.

[Sebastien Bacher (seb128)]

@Till, could you maybe try to get the delta Matthias added to our package in Debian?

http://launchpadlibrarian.net/530753441/ipp-usb_0.9.17-3_0.9.17-3ubuntu1.diff.gz

Debian isn't trying to build with LTO atm but it shouldn't make a difference to them and seems like turning off lto here is wanted

[Matthias Klose (doko)]

that delta should be dropped once golang-1.16 has the backport.

[Alexander Pevzner (pzz)]

It happens with golang-1.15 too (with LTO build), so I suggest to make this change permanent, and build without LTO.

I don't think LTO can do a lot of optimization for Go program.