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Subject[PATCH -tip 5/7] perf probe: Query basic types from debuginfo
Date
Query the basic type information (byte-size and signed-flag) from
debuginfo and pass that to kprobe-tracer. This is especially useful
for tracing the members of data structure, because each member has
different byte-size on the memory.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
---
tools/perf/util/probe-event.c | 9 +++++
tools/perf/util/probe-event.h | 1 +
tools/perf/util/probe-finder.c | 78 ++++++++++++++++++++++++++++++++++++----
3 files changed, 80 insertions(+), 8 deletions(-)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 19de8b7..05ca4a9 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -740,6 +740,13 @@ static int synthesize_kprobe_trace_arg(struct kprobe_trace_arg *arg,
buf += ret;
buflen -= ret;
}
+ /* Print argument type */
+ if (arg->type) {
+ ret = e_snprintf(buf, buflen, ":%s", arg->type);
+ if (ret <= 0)
+ return ret;
+ buf += ret;
+ }

return buf - tmp;
}
@@ -848,6 +855,8 @@ void clear_kprobe_trace_event(struct kprobe_trace_event *tev)
free(tev->args[i].name);
if (tev->args[i].value)
free(tev->args[i].value);
+ if (tev->args[i].type)
+ free(tev->args[i].type);
ref = tev->args[i].ref;
while (ref) {
next = ref->next;
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index a73ede6..0759db6 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -23,6 +23,7 @@ struct kprobe_trace_arg_ref {
struct kprobe_trace_arg {
char *name; /* Argument name */
char *value; /* Base value */
+ char *type; /* Type name */
struct kprobe_trace_arg_ref *ref; /* Referencing offset */
};

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 043140f..f3c2706 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -84,6 +84,9 @@ const char *x86_64_regs_table[X86_64_MAX_REGS] = {
#define arch_regs_table x86_32_regs_table
#endif

+/* Kprobe tracer basic type is up to u64 */
+#define MAX_BASIC_TYPE_BITS 64
+
/* Return architecture dependent register string (for kprobe-tracer) */
static const char *get_arch_regstr(unsigned int n)
{
@@ -228,6 +231,31 @@ static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
return die_mem;
}

+static bool die_is_signed_type(Dwarf_Die *tp_die)
+{
+ Dwarf_Attribute attr;
+ Dwarf_Word ret;
+
+ if (dwarf_attr(tp_die, DW_AT_encoding, &attr) == NULL ||
+ dwarf_formudata(&attr, &ret) != 0)
+ return false;
+
+ return (ret == DW_ATE_signed_char || ret == DW_ATE_signed ||
+ ret == DW_ATE_signed_fixed);
+}
+
+static int die_get_byte_size(Dwarf_Die *tp_die)
+{
+ Dwarf_Attribute attr;
+ Dwarf_Word ret;
+
+ if (dwarf_attr(tp_die, DW_AT_byte_size, &attr) == NULL ||
+ dwarf_formudata(&attr, &ret) != 0)
+ return 0;
+
+ return (int)ret;
+}
+
/* Return values for die_find callbacks */
enum {
DIE_FIND_CB_FOUND = 0, /* End of Search */
@@ -404,13 +432,42 @@ static void convert_location(Dwarf_Op *op, struct probe_finder *pf)
}
}

+static void convert_variable_type(Dwarf_Die *vr_die,
+ struct kprobe_trace_arg *targ)
+{
+ Dwarf_Die type;
+ char buf[16];
+ int ret;
+
+ if (die_get_real_type(vr_die, &type) == NULL)
+ die("Failed to get a type information of %s.",
+ dwarf_diename(vr_die));
+
+ ret = die_get_byte_size(&type) * 8;
+ if (ret) {
+ /* Check the bitwidth */
+ if (ret > MAX_BASIC_TYPE_BITS) {
+ pr_warning(" Warning: %s exceeds max-bitwidth."
+ " Cut down to %d bits.\n",
+ 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);
+ if (ret < 0 || ret >= 16)
+ die("Failed to convert variable type.");
+ targ->type = xstrdup(buf);
+ }
+}
+
static void convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
struct perf_probe_arg_field *field,
- struct kprobe_trace_arg_ref **ref_ptr)
+ struct kprobe_trace_arg_ref **ref_ptr,
+ Dwarf_Die *die_mem)
{
struct kprobe_trace_arg_ref *ref = *ref_ptr;
Dwarf_Attribute attr;
- Dwarf_Die member;
Dwarf_Die type;
Dwarf_Word offs;

@@ -444,26 +501,27 @@ static void convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
if (dwarf_tag(&type) != DW_TAG_structure_type)
die("%s is not a data structure.", varname);

- if (die_find_member(&type, field->name, &member) == NULL)
+ if (die_find_member(&type, field->name, die_mem) == NULL)
die("%s(tyep:%s) has no member %s.", varname,
dwarf_diename(&type), field->name);

/* Get the offset of the field */
- if (dwarf_attr(&member, DW_AT_data_member_location, &attr) == NULL ||
+ if (dwarf_attr(die_mem, DW_AT_data_member_location, &attr) == NULL ||
dwarf_formudata(&attr, &offs) != 0)
die("Failed to get the offset of %s.", field->name);
ref->offset += (long)offs;

/* Converting next field */
if (field->next)
- convert_variable_fields(&member, field->name, field->next,
- &ref);
+ convert_variable_fields(die_mem, field->name, field->next,
+ &ref, die_mem);
}

/* Show a variables in kprobe event format */
static void convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
{
Dwarf_Attribute attr;
+ Dwarf_Die die_mem;
Dwarf_Op *expr;
size_t nexpr;
int ret;
@@ -477,9 +535,13 @@ static void convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)

convert_location(expr, pf);

- if (pf->pvar->field)
+ if (pf->pvar->field) {
convert_variable_fields(vr_die, pf->pvar->var,
- pf->pvar->field, &pf->tvar->ref);
+ pf->pvar->field, &pf->tvar->ref,
+ &die_mem);
+ vr_die = &die_mem;
+ }
+ convert_variable_type(vr_die, pf->tvar);
/* *expr will be cached in libdw. Don't free it. */
return ;
error:

--
Masami Hiramatsu
e-mail: mhiramat@redhat.com


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