This package currently fails to build (at least on the amd64
architecture) with link time optimizations enabled.  For a background
for LTO please see

https://wiki.debian.org/ToolChain/LTO

The goal is to enable this optimization by default in an upcoming
Debian release in dpkg-buildflags for 64bit architectures.  The goal
is to get this package to build with link time optimizations, or to
explicitly disable link time optimizations for this package build.

To reproduce the build failure, enable the lto optimization in
testing/unstable by adding "optimize=+lto" to DEB_BUILD_MAINT_OPTIONS
in the debian/rules file, or if this macro is unset, just set it:

export DEB_BUILD_MAINT_OPTIONS = optimize=+lto

Please try to fix the build with lto enabled, fixing the packaging or
forwarding the issue upstream. If the issue cannot be fixed,
explicitly disallow building the package with lto by adding to your
rules file:

export DEB_BUILD_MAINT_OPTIONS = optimize=-lto

or adding that string to your existing setting of DEB_BUILD_MAINT_OPTIONS.

The full build log can be found at:
http://qa-logs.debian.net/2022/06/09/dpkglto/liblinear_2.3.0+dfsg-5_unstable_dpkglto.log
The last lines of the build log are at the end of this report.

[...]
   dh_auto_test
   create-stamp debian/debhelper-build-stamp
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
   dh_prep
   debian/rules override_dh_auto_install
make[1]: Entering directory '/<<PKGBUILDDIR>>'
dh_auto_install -- libdir=/usr/lib/x86_64-linux-gnu/
	make -j8 install DESTDIR=/<<BUILDDIR>>/liblinear-2.3.0\+dfsg/debian/tmp AM_UPDATE_INFO_DIR=no "INSTALL=install --strip-program=true" libdir=/usr/lib/x86_64-linux-gnu/
make[2]: Entering directory '/<<PKGBUILDDIR>>'
install -d /<<PKGBUILDDIR>>/debian/tmp/usr/bin/ /<<PKGBUILDDIR>>/debian/tmp/usr/lib/x86_64-linux-gnu/
install liblinear-train liblinear-predict -m 755 /<<PKGBUILDDIR>>/debian/tmp/usr/bin/
install liblinear.a -m 644 /<<PKGBUILDDIR>>/debian/tmp/usr/lib/x86_64-linux-gnu/
install liblinear.so.4.2. -m 644 /<<PKGBUILDDIR>>/debian/tmp/usr/lib/x86_64-linux-gnu/
cd /<<PKGBUILDDIR>>/debian/tmp/usr/lib/x86_64-linux-gnu/ && ln -s liblinear.so.4.2. liblinear.so.4
cd /<<PKGBUILDDIR>>/debian/tmp/usr/lib/x86_64-linux-gnu/ && ln -s liblinear.so.4 liblinear.so
make[2]: Leaving directory '/<<PKGBUILDDIR>>'
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
   dh_install
   dh_installdocs
   dh_installchangelogs
   dh_installexamples
   dh_installman
   dh_python3
   dh_lintian
   dh_perl
   dh_link
   dh_strip_nondeterminism
   dh_compress
   dh_fixperms
   debian/rules override_dh_missing
make[1]: Entering directory '/<<PKGBUILDDIR>>'
dh_missing --fail-missing
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
   dh_dwz
   dh_strip
   dh_makeshlibs
dpkg-gensymbols: error: some symbols or patterns disappeared in the symbols file: see diff output below
dpkg-gensymbols: warning: debian/liblinear4/DEBIAN/symbols doesn't match completely debian/liblinear4.symbols
--- debian/liblinear4.symbols (liblinear4_2.3.0+dfsg-5_amd64)
+++ dpkg-gensymbols5ewaCY	2022-06-10 09:07:23.290464712 +0000
@@ -21,7 +21,7 @@
  find_parameters@Base 2.3.0+dfsg
  free_and_destroy_model@Base 2.01+dfsg
  free_model_content@Base 2.01+dfsg
- (c++|optional)"function::~function()@Base" 2.01+dfsg
+#MISSING: 2.3.0+dfsg-5# (c++|optional)"function::~function()@Base" 2.01+dfsg
  get_decfun_bias@Base 2.01+dfsg
  get_decfun_coef@Base 2.01+dfsg
  get_labels@Base 2.01+dfsg
@@ -39,7 +39,7 @@
  (c++)"l2r_l2_svr_fun::fun(double*)@Base" 2.01+dfsg
  (c++)"l2r_l2_svr_fun::grad(double*, double*)@Base" 2.01+dfsg
  (c++)"l2r_l2_svr_fun::l2r_l2_svr_fun(problem const*, double*, double)@Base" 2.01+dfsg
- (c++)"l2r_l2_svr_fun::~l2r_l2_svr_fun()@Base" 2.01+dfsg
+#MISSING: 2.3.0+dfsg-5# (c++)"l2r_l2_svr_fun::~l2r_l2_svr_fun()@Base" 2.01+dfsg
  (c++)"l2r_lr_fun::Hv(double*, double*)@Base" 2.01+dfsg
  (c++)"l2r_lr_fun::XTv(double*, double*)@Base" 2.01+dfsg
  (c++)"l2r_lr_fun::Xv(double*, double*)@Base" 2.01+dfsg
@@ -66,7 +66,7 @@
  (c++)"typeinfo name for l2r_l2_svc_fun@Base" 2.01+dfsg
  (c++)"typeinfo name for l2r_l2_svr_fun@Base" 2.01+dfsg
  (c++)"typeinfo name for l2r_lr_fun@Base" 2.01+dfsg
- (c++|optional)"vtable for function@Base" 2.01+dfsg
+#MISSING: 2.3.0+dfsg-5# (c++|optional)"vtable for function@Base" 2.01+dfsg
  (c++)"vtable for l2r_l2_svc_fun@Base" 2.01+dfsg
  (c++)"vtable for l2r_l2_svr_fun@Base" 2.01+dfsg
  (c++)"vtable for l2r_lr_fun@Base" 2.01+dfsg
dh_makeshlibs: error: failing due to earlier errors
make: *** [debian/rules:36: binary] Error 25
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2