[PATCH] perf annotate: Fix crashes on empty annotate windows

[James Clark <james.clark@linaro.org>]

Annotate can open with an empty window if the disassembly tool fails.
After the linked change, the TUI started assuming there was a current
annotation line and could assert or segfault in the seek, refresh, and
source-toggle paths.

Handle empty annotate windows explicitly: set the asm entry count before
resetting the browser, return early when refreshing an empty list, and
ignore source line toggle when there is no current annotation line.

Fixes the following when opening an annotation:

  perf: ui/browser.c:125: ui_browser__list_head_seek: Assertion `pos != NULL' failed.
  Aborted

Fixes: e201757f7a0a ("perf annotate: Fix source code annotate with objdump")
Assisted-by: GitHub Copilot:GPT-5.4
Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/perf/ui/browser.c           | 3 +++
 tools/perf/ui/browsers/annotate.c | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/ui/browser.c b/tools/perf/ui/browser.c
index dc88427b4ae5..321187b204d3 100644
--- a/tools/perf/ui/browser.c
+++ b/tools/perf/ui/browser.c
@@ -513,6 +513,9 @@ unsigned int ui_browser__list_head_refresh(struct ui_browser *browser)
 	struct list_head *head = browser->entries;
 	int row = 0;
 
+	if (browser->nr_entries == 0)
+		return 0;
+
 	if (browser->top == NULL || browser->top == browser->entries)
                 browser->top = ui_browser__list_head_filter_entries(browser, head->next);
 
diff --git a/tools/perf/ui/browsers/annotate.c b/tools/perf/ui/browsers/annotate.c
index ea17e6d29a7e..0261cd922183 100644
--- a/tools/perf/ui/browsers/annotate.c
+++ b/tools/perf/ui/browsers/annotate.c
@@ -449,6 +449,9 @@ static bool annotate_browser__toggle_source(struct annotate_browser *browser,
 	struct annotation_line *al;
 	off_t offset = browser->b.index - browser->b.top_idx;
 
+	if (browser->b.nr_entries == 0)
+		return false;
+
 	browser->b.seek(&browser->b, offset, SEEK_CUR);
 	al = list_entry(browser->b.top, struct annotation_line, node);
 
@@ -542,8 +545,8 @@ static void annotate_browser__show_full_location(struct ui_browser *browser)
 static void ui_browser__init_asm_mode(struct ui_browser *browser)
 {
 	struct annotation *notes = browser__annotation(browser);
-	ui_browser__reset_index(browser);
 	browser->nr_entries = notes->src->nr_asm_entries;
+	ui_browser__reset_index(browser);
 }
 
 static int sym_title(struct symbol *sym, struct map *map, char *title,

---
base-commit: 841dbf4871c57ce2da18c4ea7ffac5487d0eda16
change-id: 20260417-james-perf-annotate-assert-20f520eeb35b

Best regards,
-- 
James Clark <james.clark@linaro.org>