[PATCH] uml: Move signal handlers to arch code

Have most signals go through an arch-provided handler which recovers the
sigcontext and then calls a generic handler.  This replaces the
ARCH_GET_SIGCONTEXT macro, which was somewhat fragile.  On x86_64, recovering
%rdx (which holds the sigcontext pointer) must be the first thing that
happens.  sig_handler duly invokes that first, but there is no guarantee that
I can see that instructions won't be reordered such that %rdx is used before
that.  Having the arch provide the handler seems much more robust.

Some signals in some parts of UML require their own handlers - these places
don't call set_handler any more.  They call sigaction or signal themselves.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 50418a5e7134..88ff0de95cd3 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -189,14 +189,25 @@ static int userspace_tramp(void *stack)
                 }
         }
         if(!ptrace_faultinfo && (stack != NULL)){
+                struct sigaction sa;
+
                 unsigned long v = UML_CONFIG_STUB_CODE +
                                   (unsigned long) stub_segv_handler -
                                   (unsigned long) &__syscall_stub_start;
 
                 set_sigstack((void *) UML_CONFIG_STUB_DATA, page_size());
-                set_handler(SIGSEGV, (void *) v, SA_ONSTACK,
-                            SIGIO, SIGWINCH, SIGALRM, SIGVTALRM,
-                            SIGUSR1, -1);
+                sigemptyset(&sa.sa_mask);
+                sigaddset(&sa.sa_mask, SIGIO);
+                sigaddset(&sa.sa_mask, SIGWINCH);
+                sigaddset(&sa.sa_mask, SIGALRM);
+                sigaddset(&sa.sa_mask, SIGVTALRM);
+                sigaddset(&sa.sa_mask, SIGUSR1);
+                sa.sa_flags = SA_ONSTACK;
+                sa.sa_handler = (void *) v;
+                sa.sa_restorer = NULL;
+                if(sigaction(SIGSEGV, &sa, NULL) < 0)
+                        panic("userspace_tramp - setting SIGSEGV handler "
+                              "failed - errno = %d\n", errno);
         }
 
         os_stop_process(os_getpid());