perf annotate: Fix fused instr logic for assembly functions

Some x86 microarchitectures fuse a subset of cmp/test/ALU instructions
with branch instructions, and thus perf annotate highlight such valid
pairs as fused.

When annotated with source, perf uses struct disasm_line to contain
either source or instruction line from objdump output. Usually, a C
statement generates multiple instructions which include such
cmp/test/ALU + branch instruction pairs. But in case of assembly
function, each individual assembly source line generate one
instruction.

The 'perf annotate' instruction fusion logic assumes the previous
disasm_line as the previous instruction line, which is wrong because,
for assembly function, previous disasm_line contains source line.  And
thus perf fails to highlight valid fused instruction pairs for assembly
functions.

Fix it by searching backward until we find an instruction line and
consider that disasm_line as fused with current branch instruction.

Before:
         │    cmpq    %rcx, RIP+8(%rsp)
    0.00 │      cmp    %rcx,0x88(%rsp)
         │    je      .Lerror_bad_iret      <--- Source line
    0.14 │   ┌──je     b4                   <--- Instruction line
         │   │movl    %ecx, %eax

After:
         │    cmpq    %rcx, RIP+8(%rsp)
    0.00 │   ┌──cmp    %rcx,0x88(%rsp)
         │   │je      .Lerror_bad_iret
    0.14 │   ├──je     b4
         │   │movl    %ecx, %eax

Reviewed-by: Jin Yao <[email protected]>
Signed-off-by: Ravi Bangoria <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kim Phillips <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Link: https //lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: Ravi Bangoria

tools/perf/ui/browser.c

@@ -757,25 +757,40 @@ void __ui_browser__line_arrow(struct ui_browser *browser, unsigned int column,
 }
 
 void ui_browser__mark_fused(struct ui_browser *browser, unsigned int column,
-			    unsigned int row, bool arrow_down)
+			    unsigned int row, int diff, bool arrow_down)
 {
-	unsigned int end_row;
+	int end_row;
 
-	if (row >= browser->top_idx)
-		end_row = row - browser->top_idx;
-	else
+	if (diff <= 0)
 		return;
 
 	SLsmg_set_char_set(1);
 
 	if (arrow_down) {
+		if (row + diff <= browser->top_idx)
+			return;
+
+		end_row = row + diff - browser->top_idx;
 		ui_browser__gotorc(browser, end_row, column - 1);
-		SLsmg_write_char(SLSMG_ULCORN_CHAR);
-		ui_browser__gotorc(browser, end_row, column);
-		SLsmg_draw_hline(2);
-		ui_browser__gotorc(browser, end_row + 1, column - 1);
 		SLsmg_write_char(SLSMG_LTEE_CHAR);
+
+		while (--end_row >= 0 && end_row > (int)(row - browser->top_idx)) {
+			ui_browser__gotorc(browser, end_row, column - 1);
+			SLsmg_draw_vline(1);
+		}
+
+		end_row = (int)(row - browser->top_idx);
+		if (end_row >= 0) {
+			ui_browser__gotorc(browser, end_row, column - 1);
+			SLsmg_write_char(SLSMG_ULCORN_CHAR);
+			ui_browser__gotorc(browser, end_row, column);
+			SLsmg_draw_hline(2);
+		}
 	} else {
+		if (row < browser->top_idx)
+			return;
+
+		end_row = row - browser->top_idx;
 		ui_browser__gotorc(browser, end_row, column - 1);
 		SLsmg_write_char(SLSMG_LTEE_CHAR);
 		ui_browser__gotorc(browser, end_row, column);

tools/perf/ui/browser.h

@@ -51,7 +51,7 @@ void ui_browser__write_graph(struct ui_browser *browser, int graph);
 void __ui_browser__line_arrow(struct ui_browser *browser, unsigned int column,
 			      u64 start, u64 end);
 void ui_browser__mark_fused(struct ui_browser *browser, unsigned int column,
-			    unsigned int row, bool arrow_down);
+			    unsigned int row, int diff, bool arrow_down);
 void __ui_browser__show_title(struct ui_browser *browser, const char *title);
 void ui_browser__show_title(struct ui_browser *browser, const char *title);
 int ui_browser__show(struct ui_browser *browser, const char *title,

tools/perf/ui/browsers/annotate.c

@@ -125,23 +125,32 @@ static void annotate_browser__write(struct ui_browser *browser, void *entry, int
 		ab->selection = al;
 }
 
-static bool is_fused(struct annotate_browser *ab, struct disasm_line *cursor)
+static int is_fused(struct annotate_browser *ab, struct disasm_line *cursor)
 {
 	struct disasm_line *pos = list_prev_entry(cursor, al.node);
 	const char *name;
+	int diff = 1;
+
+	while (pos && pos->al.offset == -1) {
+		pos = list_prev_entry(pos, al.node);
+		if (!ab->opts->hide_src_code)
+			diff++;
+	}
 
 	if (!pos)
-		return false;
+		return 0;
 
 	if (ins__is_lock(&pos->ins))
 		name = pos->ops.locked.ins.name;
 	else
 		name = pos->ins.name;
 
 	if (!name || !cursor->ins.name)
-		return false;
+		return 0;
 
-	return ins__is_fused(ab->arch, name, cursor->ins.name);
+	if (ins__is_fused(ab->arch, name, cursor->ins.name))
+		return diff;
+	return 0;
 }
 
 static void annotate_browser__draw_current_jump(struct ui_browser *browser)
@@ -155,6 +164,7 @@ static void annotate_browser__draw_current_jump(struct ui_browser *browser)
 	struct annotation *notes = symbol__annotation(sym);
 	u8 pcnt_width = annotation__pcnt_width(notes);
 	int width;
+	int diff = 0;
 
 	/* PLT symbols contain external offsets */
 	if (strstr(sym->name, "@plt"))
@@ -205,11 +215,11 @@ static void annotate_browser__draw_current_jump(struct ui_browser *browser)
 				 pcnt_width + 2 + notes->widths.addr + width,
 				 from, to);
 
-	if (is_fused(ab, cursor)) {
+	diff = is_fused(ab, cursor);
+	if (diff > 0) {
 		ui_browser__mark_fused(browser,
 				       pcnt_width + 3 + notes->widths.addr + width,
-				       from - 1,
-				       to > from);
+				       from - diff, diff, to > from);
 	}
 }