cs: constrain register-process-global to intended behavior

Make `register-process-global` check for byte strings, and avoid
retaining the byte string that it's given (in case that changes, for
example).

Closes #3053

pkgs/racket-test-core/tests/racket/foreign-test.rktl

@@ -8,6 +8,7 @@
          ffi/unsafe/alloc
          ffi/unsafe/define
          ffi/unsafe/define/conventions
+         ffi/unsafe/global
          ffi/vector
          racket/extflonum
          racket/place
@@ -1362,6 +1363,19 @@
 
 ;; ----------------------------------------
 
+(let* ([bstr (string->bytes/utf-8 (format "~a ~a" (current-inexact-milliseconds) (random)))]
+       [orig-bstr (bytes-copy bstr)])
+  (err/rt-test (register-process-global 7 8))
+  (err/rt-test (register-process-global "7" 8))
+  (test #f register-process-global bstr #f)
+  (test #f register-process-global bstr #"data\0")
+  (test #"data" cast (register-process-global bstr #f) _pointer _bytes)
+  (bytes-set! bstr 0 65)
+  (test #f register-process-global bstr #f)
+  (test #"data" cast (register-process-global orig-bstr #"data\0") _pointer _bytes))
+
+;; ----------------------------------------
+
 (report-errs)
 
 #| --- ignore everything below ---

racket/src/cs/rumble/bytes.ss

@@ -84,7 +84,8 @@
   (check who byte? b)
   (bytevector-fill! bstr b))
 
-(define bytes-copy #2%bytevector-copy)
+(define (bytes-copy bstr)
+  (#2%bytevector-copy bstr))
 
 (define-syntax-rule (define-bytes-compare name do-name)
   (define/who name

racket/src/cs/rumble/error-rewrite.ss

@@ -51,6 +51,7 @@
         (rename bytevector-u8-ref bytes-ref
                 bytevector-u8-set! bytes-set!
                 bytevector-length bytes-length
+                bytevector-copy bytes-copy
                 bitwise-arithmetic-shift arithmetic-shift
                 fixnum->flonum fx->fl 
                 flonum->fixnum fl->fx

racket/src/cs/rumble/foreign.ss

@@ -2024,7 +2024,8 @@
 
 (define process-global-table (make-hashtable equal-hash-code equal?))
 
-(define (unsafe-register-process-global key val)
+(define/who (unsafe-register-process-global key val)
+  (check who bytes? key)
   (with-global-lock
    (cond
     [(not val)
@@ -2033,7 +2034,7 @@
      (let ([old-val (hashtable-ref process-global-table key #f)])
        (cond
         [(not old-val)
-         (hashtable-set! process-global-table key val)
+         (hashtable-set! process-global-table (bytes-copy key) val)
          #f]
         [else old-val]))])))