a bounds checking code for the ARCH=x86_64

lib/alloca86_64-bt.S

@@ -0,0 +1,60 @@
+/* ---------------------------------------------- */
+/* alloca86_64.S */
+
+.globl __bound_alloca
+__bound_alloca:
+
+#ifdef TCC_TARGET_PE
+    # bound checking is not implemented
+    pop     %rdx
+    mov     %rcx,%rax
+    add     $15,%rax
+    and     $-16,%rax
+    jz      p3
+
+p1:
+    cmp     $4096,%rax
+    jbe     p2
+    test    %rax,-4096(%rsp)
+    sub     $4096,%rsp
+    sub     $4096,%rax
+    jmp p1
+p2:
+
+    sub     %rax,%rsp
+    mov     %rsp,%rax
+    add     $32,%rax
+
+p3:
+    push    %rdx
+    ret
+#else
+    pop     %rdx
+    mov     %rdi,%rax
+    movl    %rax,%rsi	# size, a second parm to the __bound_new_region
+
+    add     $15,%rax
+    and     $-16,%rax
+    jz      p3
+
+
+    sub     %rax,%rsp
+    mov     %rsp,%rdi	# pointer, a first parm to the __bound_new_region
+    mov     %rsp,%rax
+
+    push    %rdx
+    push    %rax
+    call   __bound_new_region
+    pop     %rax
+    pop     %rdx
+
+p3:
+    push    %rdx
+    ret
+#endif
+
+/* mark stack as nonexecutable */
+#if defined __ELF__ && defined __linux__
+    .section    .note.GNU-stack,"",@progbits
+#endif
+/* ---------------------------------------------- */