fuzz: remove IO commands iteratively

Now we use a one-time scan and remove strategy in the minimizer,
which is not suitable for timing dependent instructions.

For example, instruction A will indicate an address where the config
chunk locates, and instruction B will make the configuration active.
If we have the following instruction sequence:

...
A1
B1
A2
B2
...

A2 and B2 are the actual instructions that trigger the bug.

If we scan from top to bottom, after we remove A1, the behavior of B1
might be unknowable, including not to crash the program. But we will
successfully remove B1 later cause A2 and B2 will crash the process
anyway:

...
A1
A2
B2
...

Now one more trimming will remove A1.

In the perfect case, we would need to be able to remove A and B (or C!) at
the same time. But for now, let's just add a loop around the minimizer.

Since we only remove instructions, this iterative algorithm is converging.

Tested with Bug 1908062.

Signed-off-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <SYCPR01MB350263004448040ACCB9A9F1FCAB0@SYCPR01MB3502.ausprd01.prod.outlook.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

scripts/oss-fuzz/minimize_qtest_trace.py

@@ -74,21 +74,9 @@ def check_if_trace_crashes(trace, path):
     return False
 
 
-def minimize_trace(inpath, outpath):
-    global TIMEOUT
-    with open(inpath) as f:
-        trace = f.readlines()
-    start = time.time()
-    if not check_if_trace_crashes(trace, outpath):
-        sys.exit("The input qtest trace didn't cause a crash...")
-    end = time.time()
-    print("Crashed in {} seconds".format(end-start))
-    TIMEOUT = (end-start)*5
-    print("Setting the timeout for {} seconds".format(TIMEOUT))
-
-    i = 0
-    newtrace = trace[:]
+def remove_lines(newtrace, outpath):
     remove_step = 1
+    i = 0
     while i < len(newtrace):
         # 1.) Try to remove lines completely and reproduce the crash.
         # If it works, we're done.
@@ -177,7 +165,30 @@ def minimize_trace(inpath, outpath):
                     newtrace[i] = prior[0]
                     del newtrace[i+1]
         i += 1
-    check_if_trace_crashes(newtrace, outpath)
+
+
+def minimize_trace(inpath, outpath):
+    global TIMEOUT
+    with open(inpath) as f:
+        trace = f.readlines()
+    start = time.time()
+    if not check_if_trace_crashes(trace, outpath):
+        sys.exit("The input qtest trace didn't cause a crash...")
+    end = time.time()
+    print("Crashed in {} seconds".format(end-start))
+    TIMEOUT = (end-start)*5
+    print("Setting the timeout for {} seconds".format(TIMEOUT))
+
+    newtrace = trace[:]
+
+    # remove lines
+    old_len = len(newtrace) + 1
+    while(old_len > len(newtrace)):
+        old_len = len(newtrace)
+        remove_lines(newtrace, outpath)
+        newtrace = list(filter(lambda s: s != "", newtrace))
+
+    assert(check_if_trace_crashes(newtrace, outpath))
 
 
 if __name__ == '__main__':