Re: [PATCH v2 1/2] perf annotate: Fix fused instr logic for assembly functions

[Arnaldo Carvalho de Melo]

Em Sat, Sep 11, 2021 at 10:08:53AM +0530, Ravi Bangoria escreveu:
> Some x86 microarchitectures fuse a subset of cmp/test/ALU instructions
> with branch instructions, and thus perf annotate highlight such valid
> pairs as fused.

Jin, are you ok with this? Can I have your reviewed-by?

- Arnaldo
 
> 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. Perf annotate instruction fusion logic assumes previous
> disasm_line as 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
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> ---
>  tools/perf/ui/browser.c           | 33 ++++++++++++++++++++++---------
>  tools/perf/ui/browser.h           |  2 +-
>  tools/perf/ui/browsers/annotate.c | 24 +++++++++++++++-------
>  3 files changed, 42 insertions(+), 17 deletions(-)
> 
> diff --git a/tools/perf/ui/browser.c b/tools/perf/ui/browser.c
> index 781afe42e90e..fa5bd5c20e96 100644
> --- a/tools/perf/ui/browser.c
> +++ b/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);
> diff --git a/tools/perf/ui/browser.h b/tools/perf/ui/browser.h
> index 3678eb88f119..510ce4554050 100644
> --- a/tools/perf/ui/browser.h
> +++ b/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,
> diff --git a/tools/perf/ui/browsers/annotate.c b/tools/perf/ui/browsers/annotate.c
> index ef4da4295bf7..e81c2493efdf 100644
> --- a/tools/perf/ui/browsers/annotate.c
> +++ b/tools/perf/ui/browsers/annotate.c
> @@ -125,13 +125,20 @@ 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;
> @@ -139,9 +146,11 @@ static bool is_fused(struct annotate_browser *ab, struct disasm_line *cursor)
>  		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);
>  	}
>  }
>  
> -- 
> 2.27.0

-- 

- Arnaldo