commit 906bb599d4bcab9bfe31c75d7a9613c916e1b59e
author Kyle Roarty <kyleroarty1716@gmail.com> Tue Jul 20 15:02:16 2021 -0500
committer Matt Sinclair <mattdsinclair@gmail.com> Mon Jul 26 18:37:01 2021 +0000
tree 8429c0d5ca6ac830c3d77a41e98976dc508937be
parent 078dc689b969929ab0cd4687d1ae8ead67ac2b6e

sim-se: Properly handle a clone with the VFORK flag

When clone is called with the VFORK flag, the calling process is
suspended until the child process either exits, or calls execve.

This patch adds in a new variable to Process, which is used to store the
context of the calling process if this process is created through a
clone with VFORK set.

This patch also adds the required support in clone to suspend the
calling thread, and in exitImpl and execveFunc to wake up the calling
thread when the child thread calls either of those functions

Change-Id: I85af67544ea1d5df7102dcff1331b5a6f6f4fa7c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48346
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

src/sim/process.cc

diff --git a/src/sim/process.cc b/src/sim/process.cc
index 207c275..272fc9f 100644
--- a/src/sim/process.cc
+++ b/src/sim/process.cc
@@ -175,6 +175,9 @@
 #ifndef CLONE_THREAD
 #define CLONE_THREAD 0
 #endif
+#ifndef CLONE_VFORK
+#define CLONE_VFORK 0
+#endif
     if (CLONE_VM & flags) {
         /**
          * Share the process memory address space between the new process
@@ -249,6 +252,10 @@
         np->exitGroup = exitGroup;
     }
 
+    if (CLONE_VFORK & flags) {
+        np->vforkContexts.push_back(otc->contextId());
+    }
+
     np->argv.insert(np->argv.end(), argv.begin(), argv.end());
     np->envp.insert(np->envp.end(), envp.begin(), envp.end());
 }

src/sim/process.hh

diff --git a/src/sim/process.hh b/src/sim/process.hh
index 632ba90..34768a0 100644
--- a/src/sim/process.hh
+++ b/src/sim/process.hh
@@ -284,6 +284,9 @@
     // Process was forked with SIGCHLD set.
     bool *sigchld;
 
+    // Contexts to wake up when this thread exits or calls execve
+    std::vector<ContextID> vforkContexts;
+
     // Track how many system calls are executed
     statistics::Scalar numSyscalls;
 };

src/sim/syscall_emul.cc

diff --git a/src/sim/syscall_emul.cc b/src/sim/syscall_emul.cc
index 147cb39..713bec4 100644
--- a/src/sim/syscall_emul.cc
+++ b/src/sim/syscall_emul.cc
@@ -193,6 +193,16 @@
         }
     }
 
+    /**
+     * If we were a thread created by a clone with vfork set, wake up
+     * the thread that created us
+     */
+    if (!p->vforkContexts.empty()) {
+        ThreadContext *vtc = sys->threads[p->vforkContexts.front()];
+        assert(vtc->status() == ThreadContext::Suspended);
+        vtc->activate();
+    }
+
     tc->halt();
 
     /**

src/sim/syscall_emul.hh

diff --git a/src/sim/syscall_emul.hh b/src/sim/syscall_emul.hh
index 09be700..8695638 100644
--- a/src/sim/syscall_emul.hh
+++ b/src/sim/syscall_emul.hh
@@ -1521,6 +1521,10 @@
     ctc->pcState(cpc);
     ctc->activate();
 
+    if (flags & OS::TGT_CLONE_VFORK) {
+        tc->suspend();
+    }
+
     return cp->pid();
 }
 
@@ -1998,6 +2002,16 @@
     };
 
     /**
+     * If we were a thread created by a clone with vfork set, wake up
+     * the thread that created us
+     */
+    if (!p->vforkContexts.empty()) {
+        ThreadContext *vtc = p->system->threads[p->vforkContexts.front()];
+        assert(vtc->status() == ThreadContext::Suspended);
+        vtc->activate();
+    }
+
+    /**
      * Note that ProcessParams is generated by swig and there are no other
      * examples of how to create anything but this default constructor. The
      * fields are manually initialized instead of passing parameters to the