Re: [RFC PATCH v2 09/15] perf probe: Support $params without debuginfo

[Masami Hiramatsu]

On 2015/05/24 17:28, He Kuang wrote:
> When probing at function entry, fallback $params to calling regs if no
> debuginfo is provided.
> 
> Before this path:
>   $ perf probe -v --add='generic_perform_write $params'
>   ...
>   Added new event:
>   Writing event: p:probe/generic_perform_write _stext+1246632 $params
>   [86152.161204] Parse error at argument[0]. (-22)
>   Failed to write event: Invalid argument
>     Error: Failed to add events. Reason: Invalid argument (Code: -22)
> 
> After this patch:
>   $ perf probe -v --add='generic_perform_write $params'
>   ...
>   Could not open debuginfo. Try to use symbols.
>   ...
>   Added new event:
>   Writing event: p:probe/generic_perform_write _stext+1246632 %di %si %dx %cx %r8 %r9
>     probe:generic_perform_write (on generic_perform_write with $params)
> 
>   You can now use it in all perf tools, such as:
> 
>     perf record -e probe:generic_perform_write -aR sleep 1
> 
>   $ perf record -e probe:generic_perform_write dd if=/dev/zero of=/mnt/data/test bs=4k count=3

NAK, this should not work on x86-32 and we don't know how many registers are used.
I think $params special handler should be used only with debuginfo, since $params
ensures user to save function parameters with its name. If we can't do that, we
should accept that.

If you need to handle register arguments, you should introduce new $regparams instead
of $params. (however, that still not work correctly on x86-32)

Hmm, we also need $regs to record all registers.

Thank you,


> 
>   $ perf script
>   dd  1149 [000] 18574.762652: probe:generic_perform_write: (ffffffff81130770) arg1=0xffff88007c37f600 arg2=0xffff88007ca87e70 arg3=0x0 arg4=0x0 arg5=0x556062e3 arg6=0x12a8010
>   dd  1149 [000] 18574.762652: probe:generic_perform_write: (ffffffff81130770) arg1=0xffff88007c37f600 arg2=0xffff88007ca87e70 arg3=0x1000 arg4=0x0 arg5=0x556062e3 arg6=0x12a8010
>   dd  1149 [000] 18574.762652: probe:generic_perform_write: (ffffffff81130770) arg1=0xffff88007c37f600 arg2=0xffff88007ca87e70 arg3=0x2000 arg4=0x0 arg5=0x556062e3 arg6=0x12a8010
> 
> Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
> ---
>  tools/perf/util/probe-event.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index d05b77c..7f9f431 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -46,6 +46,7 @@
>  #include "probe-event.h"
>  #include "probe-finder.h"
>  #include "session.h"
> +#include <dwarf-regs.h>
>  
>  #define MAX_CMDLEN 256
>  #define PERFPROBE_GROUP "probe"
> @@ -286,6 +287,14 @@ static void clear_probe_trace_events(struct probe_trace_event *tevs, int ntevs)
>  		clear_probe_trace_event(tevs + i);
>  }
>  
> +static bool perf_probe_is_function_entry(struct perf_probe_event *pev)
> +{
> +	if (pev->point.file || pev->point.line || pev->point.lazy_line)
> +		return false;
> +
> +	return true;
> +}
> +
>  #ifdef HAVE_DWARF_SUPPORT
>  /*
>   * Some binaries like glibc have special symbols which are on the symbol
> @@ -1225,6 +1234,33 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>  	return 0;
>  }
>  
> +static char *parse_perf_probe_param(void)
> +{
> +	int i = 0;
> +	struct strbuf sb;
> +	bool first = true;
> +	const char *reg_str;
> +
> +	strbuf_init(&sb, 16);
> +
> +	while (1) {
> +		reg_str = get_arch_calling_reg_str(i++);
> +		if (!reg_str)
> +			break;
> +
> +		if (first) {
> +			strbuf_addf(&sb, "%s", reg_str);
> +			first = false;
> +		} else
> +			strbuf_addf(&sb, " %s", reg_str);
> +	}
> +
> +	if (first)
> +		strbuf_add(&sb, "", 1);
> +
> +	return strbuf_detach(&sb, NULL);
> +}
> +
>  /* Parse perf-probe event argument */
>  static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
>  {
> @@ -2543,6 +2579,12 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>  				goto nomem_out;
>  		}
>  		for (i = 0; i < tev->nargs; i++) {
> +			if (perf_probe_is_function_entry(pev) &&
> +				!strcmp(pev->args[i].var, "$params")) {
> +				tev->args[i].value = parse_perf_probe_param();
> +				continue;
> +			}
> +
>  			if (pev->args[i].name)
>  				tev->args[i].name =
>  					strdup_or_goto(pev->args[i].name,
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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