[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>

10 files changed, 102 insertions, 33 deletions

diff --git a/arch/um/os-Linux/irq.c b/arch/um/os-Linux/irq.c
index 7555bf9c33d9..a97206df5b52 100644
--- a/arch/um/os-Linux/irq.c
+++ b/arch/um/os-Linux/irq.c
@@ -132,7 +132,7 @@ void os_set_pollfd(int i, int fd)
 
 void os_set_ioignore(void)
 {
-        set_handler(SIGIO, SIG_IGN, 0, -1);
+        signal(SIGIO, SIG_IGN);
 }
 
 void init_irq_signals(int on_sigstack)
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index 90912aaca7aa..d1c5670787dc 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -67,13 +67,32 @@ static __init void do_uml_initcalls(void)
 
 static void last_ditch_exit(int sig)
 {
-        signal(SIGINT, SIG_DFL);
-        signal(SIGTERM, SIG_DFL);
-        signal(SIGHUP, SIG_DFL);
         uml_cleanup();
         exit(1);
 }
 
+static void install_fatal_handler(int sig)
+{
+        struct sigaction action;
+
+        /* All signals are enabled in this handler ... */
+        sigemptyset(&action.sa_mask);
+
+        /* ... including the signal being handled, plus we want the
+         * handler reset to the default behavior, so that if an exit
+         * handler is hanging for some reason, the UML will just die
+         * after this signal is sent a second time.
+         */
+        action.sa_flags = SA_RESETHAND | SA_NODEFER;
+        action.sa_restorer = NULL;
+        action.sa_handler = last_ditch_exit;
+        if(sigaction(sig, &action, NULL) < 0){
+                printf("failed to install handler for signal %d - errno = %d\n",
+                       errno);
+                exit(1);
+        }
+}
+
 #define UML_LIB_PATH    ":/usr/lib/uml"
 
 static void setup_env_path(void)
@@ -158,9 +177,12 @@ int main(int argc, char **argv, char **envp)
         }
         new_argv[argc] = NULL;
 
-        set_handler(SIGINT, last_ditch_exit, SA_ONESHOT | SA_NODEFER, -1);
-        set_handler(SIGTERM, last_ditch_exit, SA_ONESHOT | SA_NODEFER, -1);
-        set_handler(SIGHUP, last_ditch_exit, SA_ONESHOT | SA_NODEFER, -1);
+        /* Allow these signals to bring down a UML if all other
+         * methods of control fail.
+         */
+        install_fatal_handler(SIGINT);
+        install_fatal_handler(SIGTERM);
+        install_fatal_handler(SIGHUP);
 
         scan_elf_aux( envp);
 
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index 3afde92ad2c0..ff203625a4bd 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -246,7 +246,17 @@ void init_new_thread_stack(void *sig_stack, void (*usr1_handler)(int))
                 set_sigstack(sig_stack, pages * page_size());
                 flags = SA_ONSTACK;
         }
-        if(usr1_handler) set_handler(SIGUSR1, usr1_handler, flags, -1);
+        if(usr1_handler){
+                struct sigaction sa;
+
+                sa.sa_handler = usr1_handler;
+                sigemptyset(&sa.sa_mask);
+                sa.sa_flags = flags;
+                sa.sa_restorer = NULL;
+                if(sigaction(SIGUSR1, &sa, NULL) < 0)
+                        panic("init_new_thread_stack - sigaction failed - "
+                              "errno = %d\n", errno);
+        }
 }
 
 void init_new_thread_signals(void)
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 60e4faedf254..55b62e2b8f41 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -15,7 +15,6 @@
 #include "user.h"
 #include "signal_kern.h"
 #include "sysdep/sigcontext.h"
-#include "sysdep/signal.h"
 #include "sigcontext.h"
 #include "mode.h"
 #include "os.h"
@@ -38,18 +37,10 @@
 static int signals_enabled = 1;
 static int pending = 0;
 
-void sig_handler(ARCH_SIGHDLR_PARAM)
+void sig_handler(int sig, struct sigcontext *sc)
 {
-        struct sigcontext *sc;
         int enabled;
 
-        /* Must be the first thing that this handler does - x86_64 stores
-         * the sigcontext in %rdx, and we need to save it before it has a
-         * chance to get trashed.
-         */
-
-        ARCH_GET_SIGCONTEXT(sc, sig);
-
         enabled = signals_enabled;
         if(!enabled && (sig == SIGIO)){
                 pending |= SIGIO_MASK;
@@ -84,13 +75,10 @@ static void real_alarm_handler(int sig, struct sigcontext *sc)
 
 }
 
-void alarm_handler(ARCH_SIGHDLR_PARAM)
+void alarm_handler(int sig, struct sigcontext *sc)
 {
-        struct sigcontext *sc;
         int enabled;
 
-        ARCH_GET_SIGCONTEXT(sc, sig);
-
         enabled = signals_enabled;
         if(!signals_enabled){
                 if(sig == SIGVTALRM)
@@ -126,6 +114,10 @@ void remove_sigstack(void)
                 panic("disabling signal stack failed, errno = %d\n", errno);
 }
 
+void (*handlers[_NSIG])(int sig, struct sigcontext *sc);
+
+extern void hard_handler(int sig);
+
 void set_handler(int sig, void (*handler)(int), int flags, ...)
 {
         struct sigaction action;
@@ -133,13 +125,16 @@ void set_handler(int sig, void (*handler)(int), int flags, ...)
         sigset_t sig_mask;
         int mask;
 
-        va_start(ap, flags);
-        action.sa_handler = handler;
+        handlers[sig] = (void (*)(int, struct sigcontext *)) handler;
+        action.sa_handler = hard_handler;
+
         sigemptyset(&action.sa_mask);
-        while((mask = va_arg(ap, int)) != -1){
+
+        va_start(ap, flags);
+        while((mask = va_arg(ap, int)) != -1)
                 sigaddset(&action.sa_mask, mask);
-        }
         va_end(ap);
+
         action.sa_flags = flags;
         action.sa_restorer = NULL;
         if(sigaction(sig, &action, NULL) < 0)
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());
diff --git a/arch/um/os-Linux/sys-i386/Makefile b/arch/um/os-Linux/sys-i386/Makefile
index b3213613c41c..37806621b25d 100644
--- a/arch/um/os-Linux/sys-i386/Makefile
+++ b/arch/um/os-Linux/sys-i386/Makefile
@@ -3,7 +3,7 @@
 # Licensed under the GPL
 #
 
-obj-$(CONFIG_MODE_SKAS) = registers.o tls.o
+obj-$(CONFIG_MODE_SKAS) = registers.o signal.o tls.o
 
 USER_OBJS := $(obj-y)
 
diff --git a/arch/um/os-Linux/sys-i386/signal.c b/arch/um/os-Linux/sys-i386/signal.c
new file mode 100644
index 000000000000..0d3eae518352
--- /dev/null
+++ b/arch/um/os-Linux/sys-i386/signal.c
@@ -0,0 +1,15 @@
+/*
+ * Copyright (C) 2006 Jeff Dike (jdike@addtoit.com)
+ * Licensed under the GPL
+ */
+
+#include <signal.h>
+
+extern void (*handlers[])(int sig, struct sigcontext *sc);
+
+void hard_handler(int sig)
+{
+        struct sigcontext *sc = (struct sigcontext *) (&sig + 1);
+
+        (*handlers[sig])(sig, sc);
+}
diff --git a/arch/um/os-Linux/sys-x86_64/Makefile b/arch/um/os-Linux/sys-x86_64/Makefile
index 340ef26f5944..f67842a7735b 100644
--- a/arch/um/os-Linux/sys-x86_64/Makefile
+++ b/arch/um/os-Linux/sys-x86_64/Makefile
@@ -3,7 +3,7 @@
 # Licensed under the GPL
 #
 
-obj-$(CONFIG_MODE_SKAS) = registers.o
+obj-$(CONFIG_MODE_SKAS) = registers.o signal.o
 
 USER_OBJS := $(obj-y)
 
diff --git a/arch/um/os-Linux/sys-x86_64/signal.c b/arch/um/os-Linux/sys-x86_64/signal.c
new file mode 100644
index 000000000000..3f369e5f976b
--- /dev/null
+++ b/arch/um/os-Linux/sys-x86_64/signal.c
@@ -0,0 +1,16 @@
+/*
+ * Copyright (C) 2006 Jeff Dike (jdike@addtoit.com)
+ * Licensed under the GPL
+ */
+
+#include <signal.h>
+
+extern void (*handlers[])(int sig, struct sigcontext *sc);
+
+void hard_handler(int sig)
+{
+        struct ucontext *uc;
+        asm("movq %%rdx, %0" : "=r" (uc));
+
+        (*handlers[sig])(sig, (struct sigcontext *) &uc->uc_mcontext);
+}
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index 4ae73c0e5485..7f5ebbadca63 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -40,8 +40,8 @@ void disable_timer(void)
                 printk("disnable_timer - setitimer failed, errno = %d\n",
                        errno);
         /* If there are signals already queued, after unblocking ignore them */
-        set_handler(SIGALRM, SIG_IGN, 0, -1);
-        set_handler(SIGVTALRM, SIG_IGN, 0, -1);
+        signal(SIGALRM, SIG_IGN);
+        signal(SIGVTALRM, SIG_IGN);
 }
 
 void switch_timers(int to_real)