fix signal return for sh/fdpic

the restorer function pointer provided in the kernel sigaction
structure is interpreted by the kernel as a raw code address, not a
function descriptor.

this commit moves the declarations of the __restore and __restore_rt
symbols to ksigaction.h so that arch versions of the file can override
them, and introduces a version for sh which declares them as objects
rather than functions.

an alternate solution would have been defining SA_RESTORER to 0 so
that the functions are not used, but this both requires executable
stack (since the sh kernel does not have a vdso page with permanent
restorer functions) and crashes on qemu user-level emulation.

2 files changed, 10 insertions, 0 deletions

diff --git a/arch/mips/ksigaction.h b/arch/mips/ksigaction.h
index 6d731646..3127f7c0 100644
--- a/arch/mips/ksigaction.h
+++ b/arch/mips/ksigaction.h
@@ -7,3 +7,5 @@ struct k_sigaction {
 	 * mips-specific preprocessor conditionals in sigaction.c. */
 	void (*restorer)();
 };
+
+void __restore(), __restore_rt();
diff --git a/arch/sh/ksigaction.h b/arch/sh/ksigaction.h
new file mode 100644
index 00000000..0c652bea
--- /dev/null
+++ b/arch/sh/ksigaction.h
@@ -0,0 +1,8 @@
+struct k_sigaction {
+	void (*handler)(int);
+	unsigned long flags;
+	void *restorer;
+	unsigned mask[2];
+};
+
+extern unsigned char __restore[], __restore_rt[];