executor: fix max signal/cover filter mapping into subprocesses

There is a quirk related to posix_spawn_file_actions_adddup2:
it just executes the specified dup's in order in the child process.
In our case we do dups as follows:
20 -> 4 (output region)
4 -> 5 (max signal)
So we dup the output region onto 4 first, and then dup the same output region
(fd 4 becomes the output region) onto 5 (max signal).
So we have output region as both output region and max signal.

1 files changed, 6 insertions, 0 deletions

diff --git a/executor/executor_runner.h b/executor/executor_runner.h
index 57d63f6a7..766669dda 100644
--- a/executor/executor_runner.h
+++ b/executor/executor_runner.h
@@ -797,5 +797,11 @@ static void runner(char** argv, int argc)
 		fail("signal(SIGBUS) failed");
 
 	Connection conn(manager_addr, manager_port);
+
+	// This is required to make Subprocess fd remapping logic work.
+	// kCoverFilterFd is the largest fd we set in the child processes.
+	for (int fd = conn.FD(); fd < kCoverFilterFd;)
+		fd = dup(fd);
+
 	Runner(conn, name, argv[0]);
 }