add build note to assembler sources

When distros use the annobin compiler plugin [1], they have complete overview
what compiler flags were used for compilation and they are able to perform
security checks on the produced binaries. Compiling assembler source can't
provide this kind of information by default, so we need the explicit
-Wa,--generate-missing-build-notes=yes option during build. When the option is
missing, then the annocheck tool reports "GAPS" in the resulting binary.

binutils >= 2.31 or older with backport is needed

[1] https://fedoraproject.org/wiki/Changes/Annobin

Signed-off-by: Dan Horák <dan@danny.cz>

Author: sharkcz

configure.ac

@@ -80,12 +80,16 @@ if test "x$enable_coverage" = xno && test "x$enable_debug" = xno && test "x$enab
 	FLAGS="$FLAGS -O3 -D_FORTIFY_SOURCE=2"
 fi
 
+# check if assembler can generate missing build notes, binutils >= 2.31 or older with backport is needed
+AX_CHECK_COMPILE_FLAG([-Wa,--generate-missing-build-notes=yes], [ICA_ASFLAGS="-Wa,--generate-missing-build-notes=yes"])
+
 # restore cmdline flags (ignore PROG_AS/PROG_CC defaults)
 CFLAGS="$cmdline_CFLAGS"
 CCASFLAGS="$cmdline_CFLAGS"
 
 AC_SUBST([FLAGS], $FLAGS)
 AC_SUBST([LIBS], $LIBS)
+AC_SUBST([ICA_ASFLAGS], $ICA_ASFLAGS)
 AC_CONFIG_FILES([Makefile doc/Makefile include/Makefile src/Makefile test/Makefile])
 AC_OUTPUT
 

src/Makefile.am

@@ -8,7 +8,7 @@ lib_LTLIBRARIES = libica.la
 
 libica_la_CFLAGS = ${AM_CFLAGS} -I${srcdir}/include -I${srcdir}/../include \
 		   -fvisibility=hidden
-libica_la_CCASFLAGS = ${AM_CFLAGS}
+libica_la_CCASFLAGS = ${AM_CFLAGS} @ICA_ASFLAGS@
 libica_la_LIBADD = @LIBS@ -lrt -lcrypto
 libica_la_LDFLAGS = -Wl,--version-script=${srcdir}/../libica.map \
 		    -version-number ${VERSION}