LIB_H += util/trace-event.h
 LIB_H += util/probe-finder.h
 LIB_H += util/probe-event.h
+LIB_H += util/pstack.h
 LIB_H += util/cpumap.h
 
 LIB_OBJS += $(OUTPUT)util/abspath.o
 LIB_OBJS += $(OUTPUT)util/values.o
 LIB_OBJS += $(OUTPUT)util/debug.o
 LIB_OBJS += $(OUTPUT)util/map.o
+LIB_OBJS += $(OUTPUT)util/pstack.o
 LIB_OBJS += $(OUTPUT)util/session.o
 LIB_OBJS += $(OUTPUT)util/thread.o
 LIB_OBJS += $(OUTPUT)util/trace-event-parse.o
 
 
 #include "cache.h"
 #include "hist.h"
+#include "pstack.h"
 #include "session.h"
 #include "sort.h"
 #include "symbol.h"
        newtFormAddHotKey(self->form, 'A');
        newtFormAddHotKey(self->form, 'a');
        newtFormAddHotKey(self->form, NEWT_KEY_RIGHT);
+       newtFormAddHotKey(self->form, NEWT_KEY_LEFT);
        newtFormAddComponents(self->form, self->tree, NULL);
        self->selection = newt__symbol_tree_get_current(self->tree);
 
 int hists__browse(struct hists *self, const char *helpline, const char *input_name)
 {
        struct hist_browser *browser = hist_browser__new();
+       struct pstack *fstack = pstack__new(2);
        const struct thread *thread_filter = NULL;
        const struct dso *dso_filter = NULL;
        struct newtExitStruct es;
        if (browser == NULL)
                return -1;
 
+       fstack = pstack__new(2);
+       if (fstack == NULL)
+               goto out;
+
        ui_helpline__push(helpline);
 
        hist_browser__title(msg, sizeof(msg), input_name,
                            dso_filter, thread_filter);
        if (hist_browser__populate(browser, self, msg) < 0)
-               goto out;
+               goto out_free_stack;
 
        while (1) {
                const struct thread *thread;
                                else
                                        continue;
                        }
+
+                       if (es.u.key == NEWT_KEY_LEFT) {
+                               const void *top;
+
+                               if (pstack__empty(fstack))
+                                       continue;
+                               top = pstack__pop(fstack);
+                               if (top == &dso_filter)
+                                       goto zoom_out_dso;
+                               if (top == &thread_filter)
+                                       goto zoom_out_thread;
+                               continue;
+                       }
                }
 
                if (browser->selection->sym != NULL &&
                        hist_entry__annotate_browser(he);
                } else if (choice == zoom_dso) {
                        if (dso_filter) {
+                               pstack__remove(fstack, &dso_filter);
+zoom_out_dso:
                                ui_helpline__pop();
                                dso_filter = NULL;
                        } else {
-                               ui_helpline__fpush("To zoom out press -> + \"Zoom out of %s DSO\"",
+                               ui_helpline__fpush("To zoom out press <- or -> + \"Zoom out of %s DSO\"",
                                                   dso->kernel ? "the Kernel" : dso->short_name);
                                dso_filter = dso;
+                               pstack__push(fstack, &dso_filter);
                        }
                        hists__filter_by_dso(self, dso_filter);
                        hist_browser__title(msg, sizeof(msg), input_name,
                                goto out;
                } else if (choice == zoom_thread) {
                        if (thread_filter) {
+                               pstack__remove(fstack, &thread_filter);
+zoom_out_thread:
                                ui_helpline__pop();
                                thread_filter = NULL;
                        } else {
-                               ui_helpline__fpush("To zoom out press -> + \"Zoom out of %s(%d) thread\"",
+                               ui_helpline__fpush("To zoom out press <- or -> + \"Zoom out of %s(%d) thread\"",
                                                   thread->comm_set ? thread->comm : "",
                                                   thread->pid);
                                thread_filter = thread;
+                               pstack__push(fstack, &thread_filter);
                        }
                        hists__filter_by_thread(self, thread_filter);
                        hist_browser__title(msg, sizeof(msg), input_name,
                }
        }
        err = 0;
+out_free_stack:
+       pstack__delete(fstack);
 out:
        hist_browser__delete(browser);
        return err;
 
--- /dev/null
+/*
+ * Simple pointer stack
+ *
+ * (c) 2010 Arnaldo Carvalho de Melo <acme@redhat.com>
+ */
+
+#include "util.h"
+#include "pstack.h"
+#include <linux/kernel.h>
+#include <stdlib.h>
+
+struct pstack {
+       unsigned short  top;
+       unsigned short  max_nr_entries;
+       void            *entries[0];
+};
+
+struct pstack *pstack__new(unsigned short max_nr_entries)
+{
+       struct pstack *self = zalloc((sizeof(*self) +
+                                    max_nr_entries * sizeof(void *)));
+       if (self != NULL)
+               self->max_nr_entries = max_nr_entries;
+       return self;
+}
+
+void pstack__delete(struct pstack *self)
+{
+       free(self);
+}
+
+bool pstack__empty(const struct pstack *self)
+{
+       return self->top == 0;
+}
+
+void pstack__remove(struct pstack *self, void *key)
+{
+       unsigned short i = self->top, last_index = self->top - 1;
+
+       while (i-- != 0) {
+               if (self->entries[i] == key) {
+                       if (i < last_index)
+                               memmove(self->entries + i,
+                                       self->entries + i + 1,
+                                       (last_index - i) * sizeof(void *));
+                       --self->top;
+                       return;
+               }
+       }
+       pr_err("%s: %p not on the pstack!\n", __func__, key);
+}
+
+void pstack__push(struct pstack *self, void *key)
+{
+       if (self->top == self->max_nr_entries) {
+               pr_err("%s: top=%d, overflow!\n", __func__, self->top);
+               return;
+       }
+       self->entries[self->top++] = key;
+}
+
+void *pstack__pop(struct pstack *self)
+{
+       void *ret;
+
+       if (self->top == 0) {
+               pr_err("%s: underflow!\n", __func__);
+               return NULL;
+       }
+
+       ret = self->entries[--self->top];
+       self->entries[self->top] = NULL;
+       return ret;
+}