log: Handle dladdr failureHEADmaster

If unit/test-qmimodem-qmi times out while running under valgrind,
valgrind complains about an uninitialized value being printed during
abort signal logging. dladdr fails on the valgrind address
(0x580BCE37 in the example below) but print_backtrace still tries to
access the Dl_info structure which is not initialized. The fix is to
handle the dladdr failure gracefully.

==36318== Conditional jump or move depends on uninitialised value(s)
==36318==    at 0x4A862F8: __printf_buffer (vfprintf-process-arg.c:408)
==36318==    by 0x4AA8067: __vsnprintf_internal (vsnprintf.c:96)
==36318==    by 0x4B1D62B: __vsyslog_internal (syslog.c:220)
==36318==    by 0x4B1DB83: vsyslog (syslog.c:100)
==36318==    by 0x407C3F: ofono_error (log.c:92)
==36318==    by 0x407FEB: print_backtrace (log.c:201)
==36318==    by 0x40816B: signal_handler (log.c:228)
==36318==    by 0x580BCE37: ??? (in /usr/libexec/valgrind/memcheck-arm64-linux)

1 files changed, 4 insertions, 2 deletions

diff --git a/src/log.c b/src/log.c
index a8b4ef10e..fdfad362c 100644
--- a/src/log.c
+++ b/src/log.c
@@ -171,11 +171,13 @@ static void print_backtrace(unsigned int offset)
 
 	for (i = offset; i < n_ptrs - 1; i++) {
 		Dl_info info;
+		const char *fname = "???";
 		char addr[20], buf[PATH_MAX * 2];
 		int len, written;
 		char *ptr, *pos;
 
-		dladdr(frames[i], &info);
+		if (dladdr(frames[i], &info))
+			fname = info.dli_fname;
 
 		len = snprintf(addr, sizeof(addr), "%p\n", frames[i]);
 		if (len < 0)
@@ -199,7 +201,7 @@ static void print_backtrace(unsigned int offset)
 
 		if (strcmp(buf, "??") == 0) {
 			ofono_error("#%-2u %p in %s", i - offset,
-						frames[i], info.dli_fname);
+						frames[i], fname);
 			continue;
 		}