linux-kernel - Re: [PATCH v3 1/7] perf probe: Show correct statement line number by perf probe -l

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Date:   Mon, 18 Nov 2019 18:57:33 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v3 1/7] perf probe: Show correct statement line number by
 perf probe -l

Em Mon, Nov 18, 2019 at 05:11:50PM +0900, Masami Hiramatsu escreveu:
> The dwarf_getsrc_die() can return the line which is not a statement
> nor the least line number among the lines which shares same address.
> This can lead perf probe --list shows incorrect line number for
> probed address.
> To fix this, this introduces cu_getsrc_die() which returns only a
> statement line and which is the least line number (we call it
> the representive line for an address), and use it in cu_find_lineinfo().
> 
> Also, if the given address is the entry address of a real function,
> cu_find_lineinfo() returns the function declared line number instead
> of the start line number of the function body.
> 
> For example, without this change perf probe -l shows incorrect line
> as below.
> 
>   # perf probe -a kernel_read:2
>   Added new event:
>     probe:kernel_read    (on kernel_read:2)
> 
>   You can now use it in all perf tools, such as:
> 
>   	perf record -e probe:kernel_read -aR sleep 1
> 
>   # perf probe -l
>     probe:kernel_read    (on kernel_read:1@...ux-5.0.0/fs/read_write.c)
> 
> With this fix, it shows correct line number as below;
> 
>   # perf probe -l
>     probe:kernel_read    (on kernel_read:2@...ux-5.0.0/fs/read_write.c)

Thanks, this fixes the problem I reported, applied.

- Arnaldo
 
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  tools/perf/util/dwarf-aux.c |   62 ++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 58 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 5544bfbd0f6c..aa898014ad12 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -59,6 +59,51 @@ const char *cu_get_comp_dir(Dwarf_Die *cu_die)
>  	return dwarf_formstring(&attr);
>  }
>  
> +/* Unlike dwarf_getsrc_die(), cu_getsrc_die() only returns statement line */
> +static Dwarf_Line *cu_getsrc_die(Dwarf_Die *cu_die, Dwarf_Addr addr)
> +{
> +	Dwarf_Addr laddr;
> +	Dwarf_Lines *lines;
> +	Dwarf_Line *line;
> +	size_t nlines, l, u, n;
> +	bool flag;
> +
> +	if (dwarf_getsrclines(cu_die, &lines, &nlines) != 0 ||
> +	    nlines == 0)
> +		return NULL;
> +
> +	/* Lines are sorted by address, use binary search */
> +	l = 0; u = nlines - 1;
> +	while (l < u) {
> +		n = u - (u - l) / 2;
> +		line = dwarf_onesrcline(lines, n);
> +		if (!line || dwarf_lineaddr(line, &laddr) != 0)
> +			return NULL;
> +		if (addr < laddr)
> +			u = n - 1;
> +		else
> +			l = n;
> +	}
> +	/* Going backward to find the lowest line */
> +	do {
> +		line = dwarf_onesrcline(lines, --l);
> +		if (!line || dwarf_lineaddr(line, &laddr) != 0)
> +			return NULL;
> +	} while (laddr == addr);
> +	l++;
> +	/* Going foward to find the statement line */
> +	do {
> +		line = dwarf_onesrcline(lines, l++);
> +		if (!line || dwarf_lineaddr(line, &laddr) != 0 ||
> +		    dwarf_linebeginstatement(line, &flag) != 0)
> +			return NULL;
> +		if (laddr > addr)
> +			return NULL;
> +	} while (!flag);
> +
> +	return line;
> +}
> +
>  /**
>   * cu_find_lineinfo - Get a line number and file name for given address
>   * @cu_die: a CU DIE
> @@ -72,17 +117,26 @@ int cu_find_lineinfo(Dwarf_Die *cu_die, unsigned long addr,
>  		    const char **fname, int *lineno)
>  {
>  	Dwarf_Line *line;
> -	Dwarf_Addr laddr;
> +	Dwarf_Die die_mem;
> +	Dwarf_Addr faddr;
>  
> -	line = dwarf_getsrc_die(cu_die, (Dwarf_Addr)addr);
> -	if (line && dwarf_lineaddr(line, &laddr) == 0 &&
> -	    addr == (unsigned long)laddr && dwarf_lineno(line, lineno) == 0) {
> +	if (die_find_realfunc(cu_die, (Dwarf_Addr)addr, &die_mem)
> +	    && die_entrypc(&die_mem, &faddr) == 0 &&
> +	    faddr == addr) {
> +		*fname = dwarf_decl_file(&die_mem);
> +		dwarf_decl_line(&die_mem, lineno);
> +		goto out;
> +	}
> +
> +	line = cu_getsrc_die(cu_die, (Dwarf_Addr)addr);
> +	if (line && dwarf_lineno(line, lineno) == 0) {
>  		*fname = dwarf_linesrc(line, NULL, NULL);
>  		if (!*fname)
>  			/* line number is useless without filename */
>  			*lineno = 0;
>  	}
>  
> +out:
>  	return *lineno ?: -ENOENT;
>  }
>  

-- 

- Arnaldo