From: Nate Sammons <nate@users.sourceforge.net>
Date: Mon, 29 Mar 1999 22:57:54 +0000 (+0000)
Subject: Add capability for Linux to change a vfork call into plain fork, which
X-Git-Tag: v4.5.18~1233
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=ccd8f216267cea2f56567b8a44929475105b8298;p=strace

Add capability for Linux to change a vfork call into plain fork, which
can be followed.  (Requires a kernel patch for now.)  Also document it.
---

diff --git a/process.c b/process.c
index 5fc7744f..5ecaa16c 100644
--- a/process.c
+++ b/process.c
@@ -285,13 +285,24 @@ struct tcb *tcp;
 {
 	struct tcb *tcpchild;
 	int pid;
-	int vforking = 0;
+	int dont_follow = 0;
 
 #ifdef SYS_vfork
-	vforking = (tcp->scno == SYS_vfork);
+	if (tcp->scno == SYS_vfork) {
+#if defined(I386) && defined(LINUX)
+		/* Attempt to make vfork into fork, which we can follow. */
+		if (!followvfork || 
+		    ptrace(PTRACE_POKEUSR, tcp->pid, 
+			   (void *)(ORIG_EAX * 4), SYS_fork) < 0) 
+			dont_follow = 1;
+		
+#else
+		dont_follow = 1;
+#endif
+	}
 #endif
 	if (entering(tcp)) {
-		if (!followfork || vforking)
+		if (!followfork || dont_follow)
 			return 0;
 		if (nprocs == MAX_PROCS) {
 			tcp->flags &= ~TCB_FOLLOWFORK;
diff --git a/strace.1 b/strace.1
index 5f045f96..56e02da3 100644
--- a/strace.1
+++ b/strace.1
@@ -236,9 +236,10 @@ option is in effect, each processes trace is written to
 where pid is the numeric process id of each process.
 .TP
 .B \-F
-On SunOS 4.x, this option has the effect of attempting to follow
-vforks by performing some dynamic linking trickery.  Otherwise,
-vforks will not be followed even if
+Attempt to follow vforks.  (On SunOS 4.x, this is accomplished with
+some dynamic linking trickery.  On Linux, it requires some kernel
+functionality not yet in the standard kernel.)  Otherwise, vforks will
+not be followed even if
 .B \-f
 has been given.
 .TP