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.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/internal/ksigaction.h b/src/internal/ksigaction.h
index 2eacabf1..1d8d9646 100644
--- a/src/internal/ksigaction.h
+++ b/src/internal/ksigaction.h
@@ -7,3 +7,5 @@ struct k_sigaction {
 	void (*restorer)(void);
 	unsigned mask[2];
 };
+
+void __restore(), __restore_rt();