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

[He Kuang <hekuang@huawei.com>]

hi,

On 2015/5/24 16:49, Masami Hiramatsu wrote:
> 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

Yes, $regparam is more appropriate.

> of $params. (however, that still not work correctly on x86-32)
> 
> Hmm, we also need $regs to record all registers.

Right, I learnt regparm(3) is mandatory in x86_32, according to rules,
the first three args will go to regparm(ax, dx, cx). But we should not
refer arg1~3 to ax, dx, cx because of 64bit parameters (other reasons?).

Consider this keyword is used for generating bpf prologue which fetches
formal parameters when no debuginfo is provided, for this purpose, we can:
	1) We just help fetch the $regs or $regparms(If the keyword is
$regparms, ax/dx/cx is fetched, nothing related to args) to bpf arglists
and leave the rest things to bpf prog writer.

	2) Keep that on platforms like x86_64 and skip this feature on
platforms like x86_32.

or any other suggestions?

Thanks

> 
> 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@huawei.com>
>> ---
>>   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,
>>
> 
>