Re: [PATCH v2] perf probe: Support signedness casting

[Masami Hiramatsu]

On Fri, 5 Aug 2016 20:53:21 +0900
Naohiro Aota <naohiro.aota@xxxxxxxx> wrote:

> Perf-probe detects a variable's type and use the detected type to add new
> probe. Then, kprobes prints its variable in hexadecimal format if the
> variable is unsigned and prints in decimal if it is signed.
> 
> We sometimes want to see unsigned variable in decimal format (i.e.
> sector_t or size_t). In that case, we need to investigate variable's
> size manually to specify just signedness.
> 
> This patch add signedness casting support. By specifying "s" or "u" as a
> type, perf-probe will investigate variable size as usual and use
> the specified signedness.
> 
> E.g. without this:
> 
> $ perf probe -a 'submit_bio bio->bi_iter.bi_sector'
> Added new event:
>   probe:submit_bio     (on submit_bio with bi_sector=bio->bi_iter.bi_sector)
> You can now use it in all perf tools, such as:
>         perf record -e probe:submit_bio -aR sleep 1
> $ cat trace_pipe|head
>           dbench-9692  [003] d..1   971.096633: submit_bio: (submit_bio+0x0/0x140) bi_sector=0x3a3d00
>           dbench-9692  [003] d..1   971.096685: submit_bio: (submit_bio+0x0/0x140) bi_sector=0x1a3d80
>           dbench-9692  [003] d..1   971.096687: submit_bio: (submit_bio+0x0/0x140) bi_sector=0x3a3d80
> ...
> // need to investigate the variable size
> $ perf probe -a 'submit_bio bio->bi_iter.bi_sector:s64'
> Added new event:
>   probe:submit_bio     (on submit_bio with bi_sector=bio->bi_iter.bi_sector:s64)
> You can now use it in all perf tools, such as:
>         perf record -e probe:submit_bio -aR sleep 1
> 
> With this:
> 
> // just use "s" to cast its signedness
> $ perf probe -v -a 'submit_bio bio->bi_iter.bi_sector:s'
> Added new event:
>   probe:submit_bio     (on submit_bio with bi_sector=bio->bi_iter.bi_sector:s)
> You can now use it in all perf tools, such as:
>         perf record -e probe:submit_bio -aR sleep 1
> $ cat trace_pipe|head
>           dbench-9689  [001] d..1  1212.391237: submit_bio: (submit_bio+0x0/0x140) bi_sector=128
>           dbench-9689  [001] d..1  1212.391252: submit_bio: (submit_bio+0x0/0x140) bi_sector=131072
>           dbench-9697  [006] d..1  1212.398611: submit_bio: (submit_bio+0x0/0x140) bi_sector=30208
> 
> This commit also update perf-probe.txt to describe "types". Most parts
> are based on existing documentation: Documentation/trace/kprobetrace.txt
> 
> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxxx>
> ---
>  tools/perf/Documentation/perf-probe.txt | 10 +++++++++-
>  tools/perf/util/probe-finder.c          | 15 ++++++++++++---
>  2 files changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
> index 736da44..a23b124 100644
> --- a/tools/perf/Documentation/perf-probe.txt
> +++ b/tools/perf/Documentation/perf-probe.txt
> @@ -176,10 +176,18 @@ Each probe argument follows below syntax.
>  
>  'NAME' specifies the name of this argument (optional). You can use the name of local variable, local data structure member (e.g. var->field, var.field2), local array with fixed index (e.g. array[1], var->array[0], var->pointer[2]), or kprobe-tracer argument format (e.g. $retval, %ax, etc). Note that the name of this argument will be set as the last member name if you specify a local data structure member (e.g. field2 for 'var->field1.field2'.)
>  '$vars' and '$params' special arguments are also available for NAME, '$vars' is expanded to the local variables (including function parameters) which can access at given probe point. '$params' is expanded to only the function parameters.
> -'TYPE' casts the type of this argument (optional). If omitted, perf probe automatically set the type based on debuginfo. You can specify 'string' type only for the local variable or structure member which is an array of or a pointer to 'char' or 'unsigned char' type.
> +'TYPE' casts the type of this argument (optional). If omitted, perf probe automatically set the type based on debuginfo. Currently, basic types (u8/u16/u32/u64/s8/s16/s32/s64), "string" and bitfield are supported. (see TYPES for detail)

Hmm, have you added the 's' and 'u' here too ??

>  
>  On x86 systems %REG is always the short form of the register: for example %AX. %RAX or %EAX is not valid.
>  
> +TYPES
> +-----
> +Basic types (u8/u16/u32/u64/s8/s16/s32/s64) are integer types. Prefix 's' and 'u' means those types are signed and unsigned respectively. Traced arguments are shown in decimal (signed) or hex (unsigned). You can also use 's' or 'u' to specify only signedness and leave its size auto-detected by perf probe.

So, not only the details, but also the brief information about the TYPE, there should be 's' and 'u'.

Other are good to me.

Thanks,

> +String type is a special type, which fetches a "null-terminated" string from kernel space. This means it will fail and store NULL if the string container has been paged out. You can specify 'string' type only for the local variable or structure member which is an array of or a pointer to 'char' or 'unsigned char' type.
> +Bitfield is another special type, which takes 3 parameters, bit-width, bit-offset, and container-size (usually 32). The syntax is;
> +
> + b<bit-width>@<bit-offset>/<container-size>
> +
>  LINE SYNTAX
>  -----------
>  Line range is described by following syntax.
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index f2d9ff0..5c290c6 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -297,10 +297,13 @@ static int convert_variable_type(Dwarf_Die *vr_die,
>  	char sbuf[STRERR_BUFSIZE];
>  	int bsize, boffs, total;
>  	int ret;
> +	char sign;
>  
>  	/* TODO: check all types */
> -	if (cast && strcmp(cast, "string") != 0) {
> +	if (cast && strcmp(cast, "string") != 0 &&
> +	    strcmp(cast, "s") != 0 && strcmp(cast, "u") != 0) {
>  		/* Non string type is OK */
> +		/* and respect signedness cast */
>  		tvar->type = strdup(cast);
>  		return (tvar->type == NULL) ? -ENOMEM : 0;
>  	}
> @@ -361,6 +364,13 @@ static int convert_variable_type(Dwarf_Die *vr_die,
>  		return (tvar->type == NULL) ? -ENOMEM : 0;
>  	}
>  
> +	if (cast && (strcmp(cast, "u") == 0))
> +		sign = 'u';
> +	else if (cast && (strcmp(cast, "s") == 0))
> +		sign = 's';
> +	else
> +		sign = die_is_signed_type(&type) ? 's' : 'u';
> +
>  	ret = dwarf_bytesize(&type);
>  	if (ret <= 0)
>  		/* No size ... try to use default type */
> @@ -373,8 +383,7 @@ static int convert_variable_type(Dwarf_Die *vr_die,
>  			dwarf_diename(&type), MAX_BASIC_TYPE_BITS);
>  		ret = MAX_BASIC_TYPE_BITS;
>  	}
> -	ret = snprintf(buf, 16, "%c%d",
> -		       die_is_signed_type(&type) ? 's' : 'u', ret);
> +	ret = snprintf(buf, 16, "%c%d", sign, ret);
>  
>  formatted:
>  	if (ret < 0 || ret >= 16) {


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>