From: Dmitry V. Levin <ldv@altlinux.org>
Date: Thu, 20 Jun 2019 09:49:27 +0000 (+0000)
Subject: Implement decoding of CLONE_PIDFD flag of clone syscall
X-Git-Tag: v5.2~52
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=b28e9837acf9dc508801d58d641bf5ef7f1e9113;p=strace

Implement decoding of CLONE_PIDFD flag of clone syscall

* clone.c (SYS_FUNC(clone)): Print pidfd returned by the kernel
when CLONE_PIDFD flag is set.
* tests/clone-flags.c (main): Check it.
---

diff --git a/clone.c b/clone.c
index 66be1645..e74a53ce 100644
--- a/clone.c
+++ b/clone.c
@@ -116,13 +116,18 @@ SYS_FUNC(clone)
 		 * I'm trying to figure out whether there is a *legitimate*
 		 * use of this flag which we should respect.
 		 */
-		if ((flags & (CLONE_PARENT_SETTID|CLONE_CHILD_SETTID
+		if ((flags & (CLONE_PARENT_SETTID|CLONE_PIDFD|CLONE_CHILD_SETTID
 			      |CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0)
 			return RVAL_DECODED;
 	} else {
-		if (flags & CLONE_PARENT_SETTID) {
+		if (flags & (CLONE_PARENT_SETTID|CLONE_PIDFD)) {
+			kernel_ulong_t addr = tcp->u_arg[ARG_PTID];
+
 			tprints(", parent_tid=");
-			printnum_int(tcp, tcp->u_arg[ARG_PTID], "%u");
+			if (flags & CLONE_PARENT_SETTID)
+				printnum_int(tcp, addr, "%u");
+			else
+				printnum_fd(tcp, addr);
 		}
 		if (flags & CLONE_SETTLS) {
 			tprints(", tls=");
diff --git a/tests/clone-flags.c b/tests/clone-flags.c
index c6fb49be..b7475cfd 100644
--- a/tests/clone-flags.c
+++ b/tests/clone-flags.c
@@ -10,6 +10,7 @@
 #include "tests.h"
 
 #include <errno.h>
+#include <limits.h>
 #include <sched.h>
 #include <signal.h>
 #include <stdio.h>
@@ -17,6 +18,10 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+#define XLAT_MACROS_ONLY
+#include "xlat/clone_flags.h"
+#undef XLAT_MACROS_ONLY
+
 static const int child_exit_status = 42;
 static pid_t pid;
 
@@ -124,5 +129,23 @@ main(void)
 	       SYSCALL_NAME, child_stack_printed, STACK_SIZE_ARG
 	       "CLONE_PARENT_SETTID|SIGCHLD", *ptid, pid);
 
+	char buf[PATH_MAX];
+	if (readlink("/proc/self/fd/0", buf, sizeof(buf) - 1) > 0) {
+		*ptid = 0;
+		pid = do_clone(child, child_stack, child_stack_size,
+			       CLONE_PIDFD|SIGCHLD, 0, ptid);
+		char *fname = 0;
+		if (asprintf(&fname, "/proc/self/fd/%d", *ptid) < 0)
+			perror_msg_and_fail("asprintf");
+		int rc = readlink(fname, buf, sizeof(buf) - 1);
+		if ((unsigned int) rc >= sizeof(buf))
+			perror_msg_and_fail("readlink");
+		buf[rc] = '\0';
+		printf("%s(child_stack=%#lx" STACK_SIZE_FMT ", flags=%s"
+		       ", parent_tid=[%u<%s>]) = %d\n",
+		       SYSCALL_NAME, child_stack_printed, STACK_SIZE_ARG
+		       "CLONE_PIDFD|SIGCHLD", *ptid, buf, pid);
+	}
+
 	return 0;
 }