4 files changed, 29 insertions, 20 deletions

diff --git a/lisp/net/tramp-adb.el b/lisp/net/tramp-adb.el
index b56ffdd7bc0..f0abb277965 100644
--- a/lisp/net/tramp-adb.el
+++ b/lisp/net/tramp-adb.el
@@ -1156,8 +1156,7 @@ the exit status is not equal 0, and t otherwise."
            (format "%s; echo tramp_exit_status $?" command)
          "echo tramp_exit_status $?"))
   (with-current-buffer (tramp-get-connection-buffer vec)
-    (goto-char (point-max))
-    (unless (re-search-backward "tramp_exit_status [0-9]+" nil t)
+    (unless (tramp-search-regexp "tramp_exit_status [0-9]+")
       (tramp-error
        vec 'file-error "Couldn't find exit status of `%s'" command))
     (skip-chars-forward "^ ")
@@ -1191,9 +1190,8 @@ FMT and ARGS are passed to `error'."
             (when (re-search-forward prompt (point-at-eol) t)
               (forward-line 1)
               (delete-region (point-min) (point)))
-            (goto-char (point-max))
-            (re-search-backward prompt nil t)
-            (delete-region (point) (point-max)))
+            (when (tramp-search-regexp prompt)
+              (delete-region (point) (point-max))))
         (if timeout
             (tramp-error
              proc 'file-error
diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 8de88d355f9..506c33df466 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -5102,9 +5102,8 @@ function waits for output unless NOOUTPUT is set."
               (forward-line 1)
               (delete-region (point-min) (point)))
             ;; Delete the prompt.
-            (goto-char (point-max))
-            (re-search-backward regexp nil t)
-            (delete-region (point) (point-max)))
+            (when (tramp-search-regexp regexp)
+              (delete-region (point) (point-max))))
         (if timeout
             (tramp-error
              proc 'file-error
@@ -5134,8 +5133,7 @@ DONT-SUPPRESS-ERR is non-nil, stderr won't be sent to /dev/null."
            "echo tramp_exit_status $?"
            (if subshell " )" "")))
   (with-current-buffer (tramp-get-connection-buffer vec)
-    (goto-char (point-max))
-    (unless (re-search-backward "tramp_exit_status [0-9]+" nil t)
+    (unless (tramp-search-regexp "tramp_exit_status [0-9]+")
       (tramp-error
        vec 'file-error "Couldn't find exit status of `%s'" command))
     (skip-chars-forward "^ ")
diff --git a/lisp/net/tramp-smb.el b/lisp/net/tramp-smb.el
index 38149da6643..1a4b63d2c79 100644
--- a/lisp/net/tramp-smb.el
+++ b/lisp/net/tramp-smb.el
@@ -1451,11 +1451,10 @@ component is used as the target of the symlink."
                   (process-put p 'adjust-window-size-function #'ignore)
                   (set-process-query-on-exit-flag p nil)
                   (tramp-process-actions p v nil tramp-smb-actions-set-acl)
-                  (goto-char (point-max))
                   ;; This is meant for traces, and returning from the
                   ;; function.  No error is propagated outside, due to
                   ;; the `ignore-errors' closure.
-                  (unless (re-search-backward "tramp_exit_status [0-9]+" nil t)
+                  (unless (tramp-search-regexp "tramp_exit_status [0-9]+")
                     (tramp-error
                      v 'file-error
                      "Couldn't find exit status of `%s'" tramp-smb-acl-program))
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index e344990f7fc..f419aecbe77 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -4163,19 +4163,35 @@ for process communication also."
        (buffer-string))
       result)))
 
+(defun tramp-search-regexp (regexp)
+  "Search for REGEXP backwards, starting at point-max.
+If found, set point to the end of the occurrence found, and return point.
+Otherwise, return nil."
+  (goto-char (point-max))
+  ;; We restrict ourselves to the last 256 characters.  There were
+  ;; reports of 85kB output, which has blocked Tramp forever.
+  (re-search-backward regexp (max (point-min) (- (point) 256)) 'noerror))
+
 (defun tramp-check-for-regexp (proc regexp)
   "Check, whether REGEXP is contained in process buffer of PROC.
 Erase echoed commands if exists."
   (with-current-buffer (process-buffer proc)
     (goto-char (point-min))
 
-    ;; Check whether we need to remove echo output.
+    ;; Check whether we need to remove echo output.  The max length of
+    ;; the echo mark regexp is taken for search.  We restrict the
+    ;; search for the second echo mark to PIPE_BUF characters.
     (when (and (tramp-get-connection-property proc "check-remote-echo" nil)
-               (re-search-forward tramp-echoed-echo-mark-regexp nil t))
+               (re-search-forward
+                tramp-echoed-echo-mark-regexp
+                (+ (point) (* 5 tramp-echo-mark-marker-length)) t))
       (let ((begin (match-beginning 0)))
-        (when (re-search-forward tramp-echoed-echo-mark-regexp nil t)
+        (when
+            (re-search-forward
+             tramp-echoed-echo-mark-regexp
+             (+ (point) (tramp-get-connection-property proc "pipe-buf" 4096)) t)
           ;; Discard echo from remote output.
-          (tramp-set-connection-property proc "check-remote-echo" nil)
+          (tramp-flush-connection-property proc "check-remote-echo")
           (tramp-message proc 5 "echo-mark found")
           (forward-line 1)
           (delete-region begin (point))
@@ -4196,8 +4212,7 @@ Erase echoed commands if exists."
       ;; overflow in regexp matcher".  For example, //DIRED// lines of
       ;; directory listings with some thousand files.  Therefore, we
       ;; look from the end.
-      (goto-char (point-max))
-      (ignore-errors (re-search-backward regexp nil t)))))
+      (tramp-search-regexp regexp))))
 
 (defun tramp-wait-for-regexp (proc timeout regexp)
   "Wait for a REGEXP to appear from process PROC within TIMEOUT seconds.
@@ -4285,8 +4300,7 @@ the remote host use line-endings as defined in the variable
         (tramp-flush-connection-properties proc)
         (tramp-flush-directory-properties vec ""))
       (with-current-buffer (process-buffer proc)
-        (goto-char (point-max))
-        (when (and prompt (re-search-backward (regexp-quote prompt) nil t))
+        (when (and prompt (tramp-search-regexp (regexp-quote prompt)))
           (delete-region (point) (point-max)))))))
 
 (defun tramp-get-inode (vec)