centos8-backtrace-fix.diff

diff --git a/runtime/transport/symbols.c b/runtime/transport/symbols.c
index 91102fcaf..6b4d6dfba 100644
--- a/runtime/transport/symbols.c
+++ b/runtime/transport/symbols.c
@@ -163,7 +163,8 @@ read_sect_sysfs(const char* module, const char *section)
         char *pathname = __getname(); // PATH_MAX sized
         int rc;
         unsigned long addr = 0;
-        void *buffer = NULL;
+	char data[64] = {};
+	void *buffer = data;
 #ifdef STAPCONF_KERNEL_READ_FILE_FROM_PATH_OFFSET
         size_t size;
 #else
@@ -180,16 +181,27 @@ read_sect_sysfs(const char* module, const char *section)
                                         &buffer, 64 /* max. bytes expected */,
                                         &size /* file_size */,
                                         READING_UNKNOWN);
-#else
-        rc = kernel_read_file_from_path(pathname, &buffer, &size, 64 /* max. bytes expected */,
-                                        READING_UNKNOWN);
-#endif
         if (rc <= 0)
                 goto out1;
+#else
+	// Ignore errors because the pre-offset version of
+	// kernel_read_file_from_path() always returns a spurious error saying
+	// that we don't have enough space in our buffer. To trick it, we must
+	// set the max size to 0 (which is safe because we know the output size
+	// will only ever go up to 19 bytes on 64-bit and our buffer is 64
+	// bytes), and then pass in a pre-allocated buffer to prevent it from
+	// allocating an output buffer and then freeing it internally upon
+	// error. This allows us to inspect the buffer contents even when an
+	// error is returned.
+	kernel_read_file_from_path(pathname, &buffer, &size, 0 /* max. bytes expected */,
+				   READING_FIRMWARE_PREALLOC_BUFFER);
+	// Look for the hex prefix as a poor man's error check
+	if (data[0] != '0' || data[1] != 'x' || !data[2])
+		goto out1;
+#endif
         rc = kstrtoul(buffer, 0, &addr);
         if (rc != 0) // parse error?
                 addr = 0L;
-        vfree (buffer);
 out1:
         __putname(pathname);
 out: