Fix the value of the 'arch' variable when the current OS is 32bit on …

…a 64bit machine

src/core/opamStd.ml

@@ -991,19 +991,22 @@ module OpamSys = struct
 
   let etc () = "/etc"
 
-  let uname =
+  let memo_command =
     let memo = Hashtbl.create 7 in
-    fun arg ->
-      try Hashtbl.find memo arg with Not_found ->
+    fun cmd arg ->
+      try Hashtbl.find memo (cmd, arg) with Not_found ->
         let r =
           try
-            with_process_in "uname" arg
+            with_process_in cmd arg
               (fun ic -> Some (OpamString.strip (input_line ic)))
           with Unix.Unix_error _ | Sys_error _ | Not_found -> None
         in
-        Hashtbl.add memo arg r;
+        Hashtbl.add memo (cmd, arg) r;
         r
 
+  let uname = memo_command "uname"
+  let getconf = memo_command "getconf"
+
   let system =
     let system = Lazy.from_fun OpamStubs.getPathToSystem in
     fun () -> Lazy.force system

src/core/opamStd.mli

@@ -507,6 +507,9 @@ module Sys : sig
   (** The output of the command "uname", with the given argument. Memoised. *)
   val uname: string -> string option
 
+  (** The output of the command "getconf", with the given argument. Memoised. *)
+  val getconf: string -> string option
+
   (** Append .exe (only if missing) to executable filenames on Windows *)
   val executable_name : string -> string
 

src/state/opamSysPoll.ml

@@ -47,9 +47,23 @@ let poll_arch () =
       end
     | _ -> None
   in
-  match raw with
-  | None | Some "" -> None
-  | Some a -> Some (normalise_arch a)
+  let normalised =
+    match raw with
+    | None | Some "" -> None
+    | Some a -> Some (normalise_arch a)
+  in
+  match Sys.os_type with
+  | "Unix" | "Cygwin" ->
+    (match normalised with
+     | Some ("x86_64" | "arm64" | "ppc64" as arch) ->
+       (match OpamStd.Sys.getconf "LONG_BIT", arch with
+        | Some "32", "x86_64" -> Some "x86_32"
+        | Some "32", "arm64" -> Some "arm32"
+        | Some "32", "ppc64" -> Some "ppc32"
+        | _ -> normalised
+        | exception (Unix.Unix_error _ | Sys_error _ | Not_found) -> normalised)
+     | _ -> normalised)
+  | _ -> normalised
 let arch = Lazy.from_fun poll_arch
 
 let normalise_os raw =