Produce correct x86 assembly code for identifiers starting with $

They must be parenthesized in some contexts to avoid being confused for
immediate operands.

Fixes: #540

x86/TargetPrinter.ml

@@ -106,6 +106,7 @@ module type SYSTEM =
       val comment: string
       val raw_symbol: out_channel -> string -> unit
       val symbol: out_channel -> P.t -> unit
+      val symbol_paren: out_channel -> P.t -> unit
       val label: out_channel -> int -> unit
       val name_of_section: section_name -> string
       val stack_alignment: int
@@ -130,6 +131,12 @@ module ELF_System : SYSTEM =
 
     let symbol = elf_symbol
 
+    let symbol_paren oc symb =
+      let s = extern_atom symb in
+      if String.length s > 0 && s.[0] = '$'
+      then fprintf oc "(%s)" s
+      else fprintf oc "%s" s
+
     let label = elf_label
 
     let name_of_section = function
@@ -164,8 +171,8 @@ module ELF_System : SYSTEM =
 
     let print_mov_rs oc rd id =
       if Archi.ptr64
-      then fprintf oc "	movq    %a@GOTPCREL(%%rip), %a\n" symbol id ireg64 rd
-      else fprintf oc "	movl	$%a, %a\n" symbol id ireg32 rd
+      then fprintf oc "	movq    %a@GOTPCREL(%%rip), %a\n" symbol_paren id ireg64 rd
+      else fprintf oc "	movl	$%a, %a\n" symbol_paren id ireg32 rd
 
     let print_fun_info = elf_print_fun_info
 
@@ -196,6 +203,9 @@ module MacOS_System : SYSTEM =
     let symbol oc symb =
       raw_symbol oc (extern_atom symb)
 
+    let symbol_paren = symbol
+        (* the leading '_' protects the leading '$' *)
+
     let label oc lbl =
       fprintf oc "L%d" lbl
 
@@ -262,6 +272,12 @@ module Cygwin_System : SYSTEM =
     let symbol oc symb =
       raw_symbol oc (extern_atom symb)
 
+    let symbol_paren oc symb =
+      let s = extern_atom symb in
+      if String.length s > 0 && s.[0] = '$'
+      then fprintf oc "(%a)" raw_symbol s
+      else raw_symbol oc s
+
     let label oc lbl =
        fprintf oc "L%d" lbl
 
@@ -341,13 +357,13 @@ module Target(System: SYSTEM):TARGET =
             (* RIP-relative addressing *)
             let ofs' = Z.to_int64 ofs in
             if ofs' = 0L
-            then fprintf oc "%a(%%rip)" symbol id
+            then fprintf oc "%a(%%rip)" symbol_paren id
             else fprintf oc "(%a + %Ld)(%%rip)" symbol id ofs'
           end else begin
             (* Absolute addressing *)
             let ofs' = Z.to_int32 ofs in
             if ofs' = 0l
-            then fprintf oc "%a" symbol id
+            then fprintf oc "%a" symbol_paren id
             else fprintf oc "(%a + %ld)" symbol id ofs'
           end
       end;
@@ -707,7 +723,7 @@ module Target(System: SYSTEM):TARGET =
       | Pjmp_l(l) ->
           fprintf oc "	jmp	%a\n" label (transl_label l)
       | Pjmp_s(f, sg) ->
-          fprintf oc "	jmp	%a\n" symbol f
+          fprintf oc "	jmp	%a\n" symbol_paren f
       | Pjmp_r(r, sg) ->
           fprintf oc "	jmp	*%a\n" ireg r
       | Pjcc(c, l) ->
@@ -733,7 +749,7 @@ module Target(System: SYSTEM):TARGET =
             fprintf oc "	jmp	*%a(, %a, 4)\n" label l ireg r
           end
       | Pcall_s(f, sg) ->
-          fprintf oc "	call	%a\n" symbol f;
+          fprintf oc "	call	%a\n" symbol_paren f;
           if (not Archi.ptr64) && sg.sig_cc.cc_structret then
             fprintf oc "	pushl	%%eax\n"
       | Pcall_r(r, sg) ->