[libbacktrace] Fix strrchr segfault

Currently, when running a libbacktrace testcase t with .gnu_debuglink to
t.debug, and t.debug having a .gnu_debugaltlink to t.alt.debug, a segfault
is triggered when calling strrchr with a NULL string from
elf_find_debugfile_by_debuglink.  The NULL string originates from the elf_add
called for the .gnu_debugaltlink, which uses NULL as filename argument.

Fix this by using "" as filename argument instead.

2019-01-25  Tom de Vries  <tdevries@suse.de>

	* elf.c (elf_add): When handling .gnu_debugaltlink, call elf_add with
	filename == "".
	* Makefile.am (TESTS): Add btest_dwz_gnudebuglink.
	* Makefile.in: Regenerate.

From-SVN: r268269

libbacktrace/ChangeLog

 2019-01-25  Tom de Vries  <tdevries@suse.de>
 
+	* elf.c (elf_add): When handling .gnu_debugaltlink, call elf_add with
+	filename == "".
+	* Makefile.am (TESTS): Add btest_dwz_gnudebuglink.
+	* Makefile.in: Regenerate.
+
+2019-01-25  Tom de Vries  <tdevries@suse.de>
+
 	* Makefile.am: Rewrite dtest rule into "%_gnudebuglink" pattern rule.
 	(TESTS): Rename dtest to btest_gnudebuglink.
 	* Makefile.in: Regenerate.

libbacktrace/Makefile.am

@@ -190,6 +190,12 @@ if HAVE_DWZ
 
 TESTS += btest_dwz
 
+if HAVE_OBJCOPY_DEBUGLINK
+
+TESTS += btest_dwz_gnudebuglink
+
+endif HAVE_OBJCOPY_DEBUGLINK
+
 endif HAVE_DWZ
 
 stest_SOURCES = stest.c

libbacktrace/Makefile.in

@@ -127,11 +127,12 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__EXEEXT_2) $(am__EXEEXT_3)
 @NATIVE_TRUE@	ztest ztest_alloc edtest edtest_alloc
 @NATIVE_TRUE@am__append_2 = allocfail.sh
 @HAVE_DWZ_TRUE@@NATIVE_TRUE@am__append_3 = btest_dwz
-@HAVE_ZLIB_TRUE@@NATIVE_TRUE@am__append_4 = -lz
+@HAVE_DWZ_TRUE@@HAVE_OBJCOPY_DEBUGLINK_TRUE@@NATIVE_TRUE@am__append_4 = btest_dwz_gnudebuglink
 @HAVE_ZLIB_TRUE@@NATIVE_TRUE@am__append_5 = -lz
-@HAVE_PTHREAD_TRUE@@NATIVE_TRUE@am__append_6 = ttest ttest_alloc
-@HAVE_OBJCOPY_DEBUGLINK_TRUE@@NATIVE_TRUE@am__append_7 = btest_gnudebuglink
-@HAVE_COMPRESSED_DEBUG_TRUE@@NATIVE_TRUE@am__append_8 = ctestg ctesta \
+@HAVE_ZLIB_TRUE@@NATIVE_TRUE@am__append_6 = -lz
+@HAVE_PTHREAD_TRUE@@NATIVE_TRUE@am__append_7 = ttest ttest_alloc
+@HAVE_OBJCOPY_DEBUGLINK_TRUE@@NATIVE_TRUE@am__append_8 = btest_gnudebuglink
+@HAVE_COMPRESSED_DEBUG_TRUE@@NATIVE_TRUE@am__append_9 = ctestg ctesta \
 @HAVE_COMPRESSED_DEBUG_TRUE@@NATIVE_TRUE@	ctestg_alloc \
 @HAVE_COMPRESSED_DEBUG_TRUE@@NATIVE_TRUE@	ctesta_alloc
 subdir = .
@@ -789,7 +790,7 @@ libbacktrace_la_LIBADD = \
 
 libbacktrace_la_DEPENDENCIES = $(libbacktrace_la_LIBADD)
 TESTS = $(check_PROGRAMS) $(am__append_2) $(am__append_3) \
-	$(am__append_7)
+	$(am__append_4) $(am__append_8)
 @NATIVE_TRUE@check_LTLIBRARIES = libbacktrace_alloc.la \
 @NATIVE_TRUE@	libbacktrace_noformat.la \
 @NATIVE_TRUE@	libbacktrace_instrumented_alloc.la
@@ -834,9 +835,9 @@ TESTS = $(check_PROGRAMS) $(am__append_2) $(am__append_3) \
 @NATIVE_TRUE@stest_alloc_LDADD = libbacktrace_alloc.la
 @NATIVE_TRUE@ztest_SOURCES = ztest.c testlib.c
 @NATIVE_TRUE@ztest_CFLAGS = -DSRCDIR=\"$(srcdir)\"
-@NATIVE_TRUE@ztest_LDADD = libbacktrace.la $(am__append_4) \
+@NATIVE_TRUE@ztest_LDADD = libbacktrace.la $(am__append_5) \
 @NATIVE_TRUE@	$(CLOCK_GETTIME_LINK)
-@NATIVE_TRUE@ztest_alloc_LDADD = libbacktrace_alloc.la $(am__append_5) \
+@NATIVE_TRUE@ztest_alloc_LDADD = libbacktrace_alloc.la $(am__append_6) \
 @NATIVE_TRUE@	$(CLOCK_GETTIME_LINK)
 @NATIVE_TRUE@ztest_alloc_SOURCES = $(ztest_SOURCES)
 @NATIVE_TRUE@ztest_alloc_CFLAGS = $(ztest_CFLAGS)
@@ -1585,6 +1586,13 @@ btest_dwz.log: btest_dwz
 	--log-file $$b.log --trs-file $$b.trs \
 	$(am__common_driver_flags) $(AM_LOG_DRIVER_FLAGS) $(LOG_DRIVER_FLAGS) -- $(LOG_COMPILE) \
 	"$$tst" $(AM_TESTS_FD_REDIRECT)
+btest_dwz_gnudebuglink.log: btest_dwz_gnudebuglink
+	@p='btest_dwz_gnudebuglink'; \
+	b='btest_dwz_gnudebuglink'; \
+	$(am__check_pre) $(LOG_DRIVER) --test-name "$$f" \
+	--log-file $$b.log --trs-file $$b.trs \
+	$(am__common_driver_flags) $(AM_LOG_DRIVER_FLAGS) $(LOG_DRIVER_FLAGS) -- $(LOG_COMPILE) \
+	"$$tst" $(AM_TESTS_FD_REDIRECT)
 btest_gnudebuglink.log: btest_gnudebuglink
 	@p='btest_gnudebuglink'; \
 	b='btest_gnudebuglink'; \

libbacktrace/elf.c

@@ -3080,7 +3080,7 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 	  if (debugaltlink_view_valid)
 	    backtrace_release_view (state, &debugaltlink_view, error_callback,
 				    data);
-	  ret = elf_add (state, NULL, d, base_address, error_callback, data,
+	  ret = elf_add (state, "", d, base_address, error_callback, data,
 			 fileline_fn, found_sym, found_dwarf, NULL, 0, 1, NULL,
 			 0);
 	  if (ret < 0)