Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 85 insertions, 0 deletions

diff --git a/src/basic/raw-clone.h b/src/basic/raw-clone.h
new file mode 100644
index 0000000..6de67ab
--- /dev/null
+++ b/src/basic/raw-clone.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+/***
+  Copyright © 2016 Michael Karcher
+***/
+
+#include <errno.h>
+#include <sched.h>
+#include <sys/syscall.h>
+
+#include "log.h"
+#include "macro.h"
+#include "process-util.h"
+
+/**
+ * raw_clone() - uses clone to create a new process with clone flags
+ * @flags: Flags to pass to the clone system call
+ *
+ * Uses the clone system call to create a new process with the cloning flags and termination signal passed in the flags
+ * parameter. Opposed to glibc's clone function, using this function does not set up a separate stack for the child, but
+ * relies on copy-on-write semantics on the one stack at a common virtual address, just as fork does.
+ *
+ * To obtain copy-on-write semantics, flags must not contain CLONE_VM, and thus CLONE_THREAD and CLONE_SIGHAND (which
+ * require CLONE_VM) are not usable.
+ *
+ * Additionally, as this function does not pass the ptid, newtls and ctid parameters to the kernel, flags must not
+ * contain CLONE_PARENT_SETTID, CLONE_CHILD_SETTID, CLONE_CHILD_CLEARTID or CLONE_SETTLS.
+ *
+ * WARNING: 💣 this call (just like glibc's own clone() wrapper) will not synchronize on glibc's malloc
+ *          locks, which means they will be in an undefined state in the child if the parent is
+ *          threaded. This means: the parent must either never use threads, or the child cannot use memory
+ *          allocation itself. This is a major pitfall, hence be careful! 💣
+ *
+ * Returns: 0 in the child process and the child process id in the parent.
+ */
+static inline pid_t raw_clone(unsigned long flags) {
+        pid_t ret;
+
+        assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
+                         CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0);
+#if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
+        /* On s390/s390x and cris the order of the first and second arguments
+         * of the raw clone() system call is reversed. */
+        ret = (pid_t) syscall(__NR_clone, NULL, flags);
+#elif defined(__sparc__)
+        {
+                /**
+                 * sparc always returns the other process id in %o0, and
+                 * a boolean flag whether this is the child or the parent in
+                 * %o1. Inline assembly is needed to get the flag returned
+                 * in %o1.
+                 */
+                int in_child, child_pid, error;
+
+                asm volatile("mov %3, %%g1\n\t"
+                             "mov %4, %%o0\n\t"
+                             "mov 0 , %%o1\n\t"
+#if defined(__arch64__)
+                             "t 0x6d\n\t"
+#else
+                             "t 0x10\n\t"
+#endif
+                             "addx %%g0, 0, %2\n\t"
+                             "mov %%o1, %0\n\t"
+                             "mov %%o0, %1" :
+                             "=r"(in_child), "=r"(child_pid), "=r"(error) :
+                             "i"(__NR_clone), "r"(flags) :
+                             "%o1", "%o0", "%g1", "cc" );
+
+                if (error) {
+                        errno = child_pid;
+                        ret = -1;
+                } else
+                        ret = in_child ? 0 : child_pid;
+        }
+#else
+        ret = (pid_t) syscall(__NR_clone, flags, NULL);
+#endif
+
+        if (ret == 0)
+                reset_cached_pid();
+
+        return ret;
+}