Commit 6218bf9f authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

tracing/probe: Add immediate parameter support 

Add immediate value parameter (\1234) support to
probe events. This allows you to specify an immediate
(or dummy) parameter instead of fetching from memory
or register.

This feature looks odd, but imagine when you put a probe
on a code to trace some data. If the code is compiled into
2 instructions and 1 instruction has a value but other has
nothing since it is optimized out.
In that case, you can not fold those into one event, even
if ftrace supported multiple probes on one event.
With this feature, you can set a dummy value like
foo=\deadbeef instead of something like foo=%di.

Link: http://lkml.kernel.org/r/156095690733.28024.13258186548822649469.stgit@devnote2



Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent ab10d69e

Documentation/trace/kprobetrace.rst

+1 −0
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ Synopsis of kprobe_events 
  $retval	: Fetch return value.(\*2)

  $comm		: Fetch current task comm.

  +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4)

  \IMM		: Store an immediate value to the argument.

  NAME=FETCHARG : Set NAME as the argument name of FETCHARG.

  FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types

		  (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types

Documentation/trace/uprobetracer.rst

+1 −0
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ Synopsis of uprobe_tracer 
   $retval	: Fetch return value.(\*1)

   $comm	: Fetch current task comm.

   +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*2)(\*3)

   \IMM		: Store an immediate value to the argument.

   NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.

   FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types

		       (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types

kernel/trace/trace.c

+1 −1
Original line number Diff line number Diff line
@@ -4848,7 +4848,7 @@ static const char readme_msg[] = 
#else

	"\t           $stack<index>, $stack, $retval, $comm,\n"

#endif

	"\t           +|-[u]<offset>(<fetcharg>)\n"

	"\t           +|-[u]<offset>(<fetcharg>), \\imm-value\n"

	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol,\n"

	"\t           b<bit-width>@<bit-offset>/<container-size>, ustring,\n"

	"\t           <type>\\[<array-size>\\]\n"

kernel/trace/trace_probe.c

+18 −0
Original line number Diff line number Diff line
@@ -316,6 +316,17 @@ inval_var: 
	return -EINVAL;

}



static int str_to_immediate(char *str, unsigned long *imm)

{

	if (isdigit(str[0]))

		return kstrtoul(str, 0, imm);

	else if (str[0] == '-')

		return kstrtol(str, 0, (long *)imm);

	else if (str[0] == '+')

		return kstrtol(str + 1, 0, (long *)imm);

	return -EINVAL;

}



/* Recursive argument parser */

static int

parse_probe_arg(char *arg, const struct fetch_type *type,
@@ -444,6 +455,13 @@ parse_probe_arg(char *arg, const struct fetch_type *type, 
			code->offset = offset;

		}

		break;

	case '\\':	/* Immediate value */

		ret = str_to_immediate(arg + 1, &code->immediate);

		if (ret)

			trace_probe_log_err(offs + 1, BAD_IMM);

		else

			code->op = FETCH_OP_IMM;

		break;

	}

	if (!ret && code->op == FETCH_OP_NOP) {

		/* Parsed, but do not find fetch method */

kernel/trace/trace_probe.h

+1 −0
Original line number Diff line number Diff line
@@ -408,6 +408,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call, 
	C(BAD_VAR,		"Invalid $-valiable specified"),	\

	C(BAD_REG_NAME,		"Invalid register name"),		\

	C(BAD_MEM_ADDR,		"Invalid memory address"),		\

	C(BAD_IMM,		"Invalid immediate value"),		\

	C(FILE_ON_KPROBE,	"File offset is not available with kprobe"), \

	C(BAD_FILE_OFFS,	"Invalid file offset value"),		\

	C(SYM_ON_UPROBE,	"Symbol is not available with uprobe"),	\

CRA Git | Maintained and supported by SUSTech CRA and CCSE