clone.2, sigaltstack.2: clone(CLONE_VM) disdables the alternate signal stack

In the kernel sources (kernel/fork.c::copy_process()), we have:

        /*
         * sigaltstack should be cleared when sharing the same VM
         */
        if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
                sas_ss_reset(p);

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

2 files changed, 17 insertions, 0 deletions

diff --git a/man2/clone.2 b/man2/clone.2
index b013550b67..976738f7d8 100644
--- a/man2/clone.2
+++ b/man2/clone.2
@@ -1181,6 +1181,15 @@ space of the calling process at the time of the clone call.
 Memory writes or file mappings/unmappings performed by one of the
 processes do not affect the other, as with
 .BR fork (2).
+.IP
+If the
+.BR CLONE_VM
+flag is specified and the
+.BR CLONE_VM
+flag is not specified,
+then any alternate signal stack that was established by
+.BR sigaltstack (2)
+is cleared in the child process.
 .SH RETURN VALUE
 .\" gettid(2) returns current->pid;
 .\" getpid(2) returns current->tgid;
diff --git a/man2/sigaltstack.2 b/man2/sigaltstack.2
index d6eaea830f..aada8ff693 100644
--- a/man2/sigaltstack.2
+++ b/man2/sigaltstack.2
@@ -269,6 +269,14 @@ signal stack.
 A child process created via
 .BR fork (2)
 inherits a copy of its parent's alternate signal stack settings.
+The same is also true for a child process created using
+.BR clone (2),
+unless the clone flags include
+.BR CLONE_VM
+and do not include
+.BR CLONE_VFORK ,
+in which case any alternate signal stack that was established in the parent
+is disabled in the child process.
 .PP
 .BR sigaltstack ()
 supersedes the older