[klibc] alpha: Pass restorer to rt_sigaction() and disable executable stack

alpha does not support the SA_RESTORER flag, but allows specifiying a
restorer callback as an additional parameter to rt_sigaction().  We
should do this to avoid needing an executable stack.

* Force the SA_SIGINFO flag on for all signal handlers, so that we can
  always return from them with rt_sigreturn
* Define a __sigreturn() routine that calls rt_sigreturn
* Pass that routine as the last argument to rt_sigaction()
* Set KLIBCEXECSTACK=n

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

5 files changed, 25 insertions, 6 deletions

diff --git a/usr/include/arch/alpha/klibc/archconfig.h b/usr/include/arch/alpha/klibc/archconfig.h
index 272fee0ad3560..9d28db12f0add 100644
--- a/usr/include/arch/alpha/klibc/archconfig.h
+++ b/usr/include/arch/alpha/klibc/archconfig.h
@@ -10,6 +10,8 @@
 #define _KLIBC_ARCHCONFIG_H
 
 #define _KLIBC_USE_RT_SIG 1
+/* We provide our own restorer that call rt_sigreturn() */
+#define _KLIBC_NEEDS_SA_SIGINFO 1
 #define _KLIBC_STATFS_F_TYPE_64 0
 
 #endif				/* _KLIBC_ARCHCONFIG_H */
diff --git a/usr/klibc/arch/alpha/Kbuild b/usr/klibc/arch/alpha/Kbuild
index 2e566eb6fbc1d..89386aeaddc9d 100644
--- a/usr/klibc/arch/alpha/Kbuild
+++ b/usr/klibc/arch/alpha/Kbuild
@@ -9,7 +9,7 @@
 
 always  := crt0.o
 targets := crt0.o
-klib-y := pipe.o setjmp.o syscall.o sysdual.o
+klib-y := pipe.o setjmp.o sigreturn.o syscall.o sysdual.o
 
 # Special CFLAGS for the divide code
 DIVCFLAGS = $(KLIBCREQFLAGS) $(KLIBCARCHREQFLAGS) \
diff --git a/usr/klibc/arch/alpha/MCONFIG b/usr/klibc/arch/alpha/MCONFIG
index 072adb8574f7b..e71db264253f3 100644
--- a/usr/klibc/arch/alpha/MCONFIG
+++ b/usr/klibc/arch/alpha/MCONFIG
@@ -15,6 +15,5 @@ KLIBCBITSIZE  = 64
 # the binary.
 KLIBCSHAREDFLAGS	= -Ttext-segment 0x1c0000000
 
-# Kernel uses stack trampoline for signal return unless we set
-# sa_restorer
-KLIBCEXECSTACK := y
+# Kernel uses our sa_restorer for signal return
+KLIBCEXECSTACK := n
diff --git a/usr/klibc/arch/alpha/sigreturn.S b/usr/klibc/arch/alpha/sigreturn.S
new file mode 100644
index 0000000000000..a979b7a347e5c
--- /dev/null
+++ b/usr/klibc/arch/alpha/sigreturn.S
@@ -0,0 +1,18 @@
+/*
+ * arch/alpha/sigreturn.S
+ */
+
+#include <machine/asm.h>
+#include <asm/unistd.h>
+
+	.text
+	.align	3
+	.type	__sigreturn,@function
+	.ent	__sigreturn,0
+	.globl	__sigreturn
+__sigreturn:
+	mov	sp,a0			# struct sigcontext on stack
+	lda	v0,__NR_rt_sigreturn(zero)
+	callsys
+	.size	__sigreturn,.-__sigreturn
+	.end	__sigreturn
diff --git a/usr/klibc/sigaction.c b/usr/klibc/sigaction.c
index 0d7c5c9dac35f..789494dbb97db 100644
--- a/usr/klibc/sigaction.c
+++ b/usr/klibc/sigaction.c
@@ -14,7 +14,7 @@ __extern int __rt_sigaction(int, const struct sigaction *, struct sigaction *,
 			    void (*)(void), size_t);
 #elif defined(__alpha__)
 __extern int __rt_sigaction(int, const struct sigaction *, struct sigaction *,
-			    size_t, void *);
+			    size_t, void (*)(void));
 #else
 __extern int __rt_sigaction(int, const struct sigaction *, struct sigaction *,
 			    size_t);
@@ -60,7 +60,7 @@ int sigaction(int sig, const struct sigaction *act, struct sigaction *oact)
 		rv = __rt_sigaction(sig, act, oact, restorer, sizeof(sigset_t));
 	}
 # elif defined(__alpha__)
-	rv = __rt_sigaction(sig, act, oact, sizeof(sigset_t), NULL);
+	rv = __rt_sigaction(sig, act, oact, sizeof(sigset_t), &__sigreturn);
 # else
 	rv = __rt_sigaction(sig, act, oact, sizeof(sigset_t));
 # endif