libctf: fix ELF-in-BFD checks in the presence of ASAN

The address sanitizer contains a redirector that captures dlopen calls,
so checks for dlopen with AC_SEARCH_LIBS will always conclude that
dlopen is present when the sanitizer is on.  This means it won't add
-ldl to LIBS even if needed, and the immediately-following attempt to
actually link with -lbfd will fail because libbfd also needs dlsym,
which ASAN does *not* contain a redirector for.

If we check for dlsym instead of dlopen, the check works whether ASAN is
on or off.  (bfd uses both in close proximity: if it needs one, it will
always need the other.)

libctf/ChangeLog
2021-03-25  Nick Alcock  <nick.alcock@oracle.com>

	* configure.ac: Check for dlsym, not dlopen.
	* configure: Regenerate.

3 files changed, 18 insertions, 13 deletions

diff --git a/libctf/ChangeLog b/libctf/ChangeLog
index d4a94bb27c..e66224a4fd 100644
--- a/libctf/ChangeLog
+++ b/libctf/ChangeLog
@@ -1,5 +1,10 @@
 2021-03-25  Nick Alcock  <nick.alcock@oracle.com>
 
+	* configure.ac: Check for dlsym, not dlopen.
+	* configure: Regenerate.
+
+2021-03-25  Nick Alcock  <nick.alcock@oracle.com>
+
 	* testsuite/libctf-writable/symtypetab-nonlinker-writeout.c: Don't
 	leak buf.
 
diff --git a/libctf/configure b/libctf/configure
index 61f4db4767..82bcf13a60 100755
--- a/libctf/configure
+++ b/libctf/configure
@@ -12798,9 +12798,9 @@ fi
 rm -f conftest.mmap conftest.txt
 
 # Needed for BFD capability checks.
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for library containing dlopen" >&5
-$as_echo_n "checking for library containing dlopen... " >&6; }
-if ${ac_cv_search_dlopen+:} false; then :
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for library containing dlsym" >&5
+$as_echo_n "checking for library containing dlsym... " >&6; }
+if ${ac_cv_search_dlsym+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   ac_func_search_save_LIBS=$LIBS
@@ -12813,11 +12813,11 @@ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 #ifdef __cplusplus
 extern "C"
 #endif
-char dlopen ();
+char dlsym ();
 int
 main ()
 {
-return dlopen ();
+return dlsym ();
   ;
   return 0;
 }
@@ -12830,25 +12830,25 @@ for ac_lib in '' dl; do
     LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
   fi
   if ac_fn_c_try_link "$LINENO"; then :
-  ac_cv_search_dlopen=$ac_res
+  ac_cv_search_dlsym=$ac_res
 fi
 rm -f core conftest.err conftest.$ac_objext \
     conftest$ac_exeext
-  if ${ac_cv_search_dlopen+:} false; then :
+  if ${ac_cv_search_dlsym+:} false; then :
   break
 fi
 done
-if ${ac_cv_search_dlopen+:} false; then :
+if ${ac_cv_search_dlsym+:} false; then :
 
 else
-  ac_cv_search_dlopen=no
+  ac_cv_search_dlsym=no
 fi
 rm conftest.$ac_ext
 LIBS=$ac_func_search_save_LIBS
 fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_search_dlopen" >&5
-$as_echo "$ac_cv_search_dlopen" >&6; }
-ac_res=$ac_cv_search_dlopen
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_search_dlsym" >&5
+$as_echo "$ac_cv_search_dlsym" >&6; }
+ac_res=$ac_cv_search_dlsym
 if test "$ac_res" != no; then :
   test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
 
diff --git a/libctf/configure.ac b/libctf/configure.ac
index ae1f10d1f2..80644b89d6 100644
--- a/libctf/configure.ac
+++ b/libctf/configure.ac
@@ -68,7 +68,7 @@ ACX_PROG_CC_WARNING_OPTS([-Wall], [ac_libctf_warn_cflags])
 
 AC_FUNC_MMAP
 # Needed for BFD capability checks.
-AC_SEARCH_LIBS(dlopen, dl)
+AC_SEARCH_LIBS(dlsym, dl)
 AM_ZLIB
 
 GCC_ENABLE([libctf-hash-debugging], [no], [], [Enable expensive debugging of CTF deduplication type hashing])