[compiler-rt] libFuzzer: update -merge_control_file= help message.

Summary:
The motivation for this change is to have a distinguisher in libFuzzer
that would let the runner know whether multistep merge is supported or not by
a particular fuzz target binary. Otherwise, multistep merge fails to execute
with older version of libFuzzer, and there is no way to verify that easily.

Reviewers: kcc

Subscribers: dberris, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D71423

diff --git a/compiler-rt/lib/fuzzer/FuzzerFlags.def b/compiler-rt/lib/fuzzer/FuzzerFlags.def
index 0e19a9c..a674157 100644 (file)
--- a/compiler-rt/lib/fuzzer/FuzzerFlags.def
+++ b/compiler-rt/lib/fuzzer/FuzzerFlags.def
@@ -56,7 +56,8 @@ FUZZER_FLAG_STRING(merge_control_file,
                    "Specify a control file used for the merge process. "
                    "If a merge process gets killed it tries to leave this file "
                    "in a state suitable for resuming the merge. "
-                   "By default a temporary file will be used.")
+                   "By default a temporary file will be used."
+                   "The same file can be used for multistep merge process.")
 FUZZER_FLAG_INT(minimize_crash, 0, "If 1, minimizes the provided"
   " crash input. Use with -runs=N or -max_total_time=N to limit "
   "the number attempts."