add sigaltstack syscall
diff --git a/libc/arch-sh/syscalls/sigaltstack.S b/libc/arch-sh/syscalls/sigaltstack.S
new file mode 100644
index 0000000..8b03e27
--- /dev/null
+++ b/libc/arch-sh/syscalls/sigaltstack.S
@@ -0,0 +1,32 @@
+/* autogenerated by gensyscalls.py */
+#include <sys/linux-syscalls.h>
+
+ .text
+ .type sigaltstack, @function
+ .globl sigaltstack
+ .align 4
+
+sigaltstack:
+
+ /* invoke trap */
+ mov.l 0f, r3 /* trap num */
+ trapa #(2 + 0x10)
+
+ /* check return value */
+ cmp/pz r0
+ bt __NR_sigaltstack_end
+
+ /* keep error number */
+ sts.l pr, @-r15
+ mov.l 1f, r1
+ jsr @r1
+ mov r0, r4
+ lds.l @r15+, pr
+
+__NR_sigaltstack_end:
+ rts
+ nop
+
+ .align 2
+0: .long __NR_sigaltstack
+1: .long __set_syscall_errno