[PATCH] restore: Add restoration of alternative signal stack

[Cyrill Gorcunov]

To restore SAS we have two ways:
- call for sigaltstack explicitly in restorer.c right before we call for sigreturn
- pass stack value to sigreturn call and allow the kernel to restore stack for us

Since second way is a simplier one -- we stick with it.

[alekskartashov@: use RT_SIGFRAME_UC]
Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
CC: Alexander Kartashov <alekskartashov at parallels.com>
---
 cr-restore.c       |  5 +++++
 include/restorer.h |  2 ++
 include/sigframe.h | 17 +++++++++++++++++
 pie/restorer.c     |  9 +++++++++
 sigframe.c         | 12 ++++++++++++
 5 files changed, 45 insertions(+)

diff --git a/cr-restore.c b/cr-restore.c
index 2146da2..b9beb02 100644
--- a/cr-restore.c
+++ b/cr-restore.c
@@ -2153,6 +2153,11 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core)
 	if (prepare_rlimits(pid, task_args))
 		goto err;
 
+	if (core->thread_core->sas)
+		task_args->sas = *core->thread_core->sas;
+	else
+		task_args->sas.ss_sp = (u64)SAS_INVALID_SP;
+
 	/*
 	 * Fill up per-thread data.
 	 */
diff --git a/include/restorer.h b/include/restorer.h
index 8a796a5..073dec9 100644
--- a/include/restorer.h
+++ b/include/restorer.h
@@ -153,6 +153,8 @@ struct task_restore_core_args {
 
 	struct vdso_symtable		vdso_sym_rt;		/* runtime vdso symbols */
 	unsigned long			vdso_rt_parked_at;	/* safe place to keep vdso */
+
+	ThreadSasEntry			sas;
 } __aligned(sizeof(long));
 
 #define SHMEMS_SIZE	4096
diff --git a/include/sigframe.h b/include/sigframe.h
index afc2c9d..65edaa4 100644
--- a/include/sigframe.h
+++ b/include/sigframe.h
@@ -5,6 +5,8 @@
 #ifndef __CR_SIGFRAME_H__
 #define __CR_SIGFRAME_H__
 
+#include "protobuf/core.pb-c.h"
+
 struct rt_sigframe;
 
 #ifndef __ARCH_SI_PREAMBLE_SIZE
@@ -43,4 +45,19 @@ extern int construct_sigframe(struct rt_sigframe *sigframe,
 			      struct rt_sigframe *rsigframe,
 			      CoreEntry *core);
 
+#define SAS_INVALID_SP		(-1ull)
+/*
+ * FIXME Convert it to inline helper, which requires
+ *	 to unweave types mess we've generated for
+ *	 run-time data.
+ */
+#define setup_sas(sigframe, sas)											\
+do {															\
+	if ((sas)) {													\
+		RT_SIGFRAME_UC((sigframe)).uc_stack.ss_sp	= (void *)decode_pointer((sas)->ss_sp);			\
+		RT_SIGFRAME_UC((sigframe)).uc_stack.ss_flags	= (int)(sas)->ss_flags;					\
+		RT_SIGFRAME_UC((sigframe)).uc_stack.ss_size	= (size_t)(sas)->ss_size;				\
+	}																						\
+} while (0)
+
 #endif /* __CR_SIGFRAME_H__ */
diff --git a/pie/restorer.c b/pie/restorer.c
index f1b1ca2..1cacb79 100644
--- a/pie/restorer.c
+++ b/pie/restorer.c
@@ -784,6 +784,15 @@ long __export_restore_task(struct task_restore_core_args *args)
 		goto core_restore_end;
 
 	/*
+	 * FIXME
+	 * Alternative signal stack for the group leader
+	 * is setting up separately from the threads.
+	 * This better should be unified one day.
+	 */
+	if (args->sas.ss_sp != (u64)SAS_INVALID_SP)
+		setup_sas(rt_sigframe, &args->sas);
+
+	/*
 	 * Threads restoration. This requires some more comments. This
 	 * restorer routine and thread restorer routine has the following
 	 * memory map, prepared by a caller code.
diff --git a/sigframe.c b/sigframe.c
index 68c9776..053bdf0 100644
--- a/sigframe.c
+++ b/sigframe.c
@@ -31,5 +31,17 @@ int construct_sigframe(struct rt_sigframe *sigframe,
 	if (restore_gpregs(sigframe, CORE_THREAD_ARCH_INFO(core)->gpregs))
 		return -1;
 
+	/*
+	 * On restore we have 2 ways for sas
+	 * - either call for sigaltstack explicitly in restorer.c right before
+	 *   we call for sigreturn
+	 *
+	 * - either pass stack value to sigreturn call and allow the kernel to
+	 *   restore stack for us
+	 *
+	 * Second way looks more clean and simple, and here we go.
+	 */
+	setup_sas(sigframe, core->thread_core->sas);
+
 	return 0;
 }
-- 
1.8.1.4


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