[PATCH 5/5] perf probe: Support static and global variables

Arnaldo Carvalho de Melo
2010-07-06T01:05:11Z

From: Masami Hiramatsu <mhiramat@redhat.com>

Add static and global variables support to perf probe.
This allows user to trace non-local variables (and
structure members) at probe points.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100519195749.2885.17451.stgit@localhost6.localdomain6>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/probe-event.c | 15 ++++++-
tools/perf/util/probe-finder.c | 85 ++++++++++++++++++++++++++++-----------
2 files changed, 73 insertions(+), 27 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 351baa9..09cf546 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -926,6 +926,7 @@ out:
static int synthesize_kprobe_trace_arg(struct kprobe_trace_arg *arg,
char *buf, size_t buflen)
{
+ struct kprobe_trace_arg_ref *ref = arg->ref;
int ret, depth = 0;
char *tmp = buf;

@@ -939,16 +940,24 @@ static int synthesize_kprobe_trace_arg(struct kprobe_trace_arg *arg,
buf += ret;
buflen -= ret;

+ /* Special case: @XXX */
+ if (arg->value[0] == '@' && arg->ref)
+ ref = ref->next;
+
/* Dereferencing arguments */
- if (arg->ref) {
- depth = __synthesize_kprobe_trace_arg_ref(arg->ref, &buf,
+ if (ref) {
+ depth = __synthesize_kprobe_trace_arg_ref(ref, &buf,
&buflen, 1);
if (depth < 0)
return depth;
}

/* Print argument value */
- ret = e_snprintf(buf, buflen, "%s", arg->value);
+ if (arg->value[0] == '@' && arg->ref)
+ ret = e_snprintf(buf, buflen, "%s%+ld", arg->value,
+ arg->ref->offset);
+ else
+ ret = e_snprintf(buf, buflen, "%s", arg->value);
if (ret < 0)
return ret;
buf += ret;
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 308664d..3e64e1f 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -406,14 +406,50 @@ static Dwarf_Die *die_find_member(Dwarf_Die *st_die, const char *name,
* Probe finder related functions
*/

+static struct kprobe_trace_arg_ref *alloc_trace_arg_ref(long offs)
+{
+ struct kprobe_trace_arg_ref *ref;
+ ref = zalloc(sizeof(struct kprobe_trace_arg_ref));
+ if (ref != NULL)
+ ref->offset = offs;
+ return ref;
+}
+
/* Show a location */
-static int convert_location(Dwarf_Op *op, struct probe_finder *pf)
+static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
{
+ Dwarf_Attribute attr;
+ Dwarf_Op *op;
+ size_t nops;
unsigned int regn;
Dwarf_Word offs = 0;
bool ref = false;
const char *regs;
struct kprobe_trace_arg *tvar = pf->tvar;
+ int ret;
+
+ /* TODO: handle more than 1 exprs */
+ if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL ||
+ dwarf_getlocation_addr(&attr, pf->addr, &op, &nops, 1) <= 0 ||
+ nops == 0) {
+ /* TODO: Support const_value */
+ pr_err("Failed to find the location of %s at this address.\n"
+ " Perhaps, it has been optimized out.\n", pf->pvar->var);
+ return -ENOENT;
+ }
+
+ if (op->atom == DW_OP_addr) {
+ /* Static variables on memory (not stack), make @varname */
+ ret = strlen(dwarf_diename(vr_die));
+ tvar->value = zalloc(ret + 2);
+ if (tvar->value == NULL)
+ return -ENOMEM;
+ snprintf(tvar->value, ret + 2, "@%s", dwarf_diename(vr_die));
+ tvar->ref = alloc_trace_arg_ref((long)offs);
+ if (tvar->ref == NULL)
+ return -ENOMEM;
+ return 0;
+ }

/* If this is based on frame buffer, set the offset */
if (op->atom == DW_OP_fbreg) {
@@ -455,10 +491,9 @@ static int convert_location(Dwarf_Op *op, struct probe_finder *pf)
return -ENOMEM;

if (ref) {
- tvar->ref = zalloc(sizeof(struct kprobe_trace_arg_ref));
+ tvar->ref = alloc_trace_arg_ref((long)offs);
if (tvar->ref == NULL)
return -ENOMEM;
- tvar->ref->offset = (long)offs;
}
return 0;
}
@@ -666,20 +701,13 @@ next:
/* Show a variables in kprobe event format */
static int 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;

- if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL)
- goto error;
- /* TODO: handle more than 1 exprs */
- ret = dwarf_getlocation_addr(&attr, pf->addr, &expr, &nexpr, 1);
- if (ret <= 0 || nexpr == 0)
- goto error;
+ pr_debug("Converting variable %s into trace event.\n",
+ dwarf_diename(vr_die));

- ret = convert_location(expr, pf);
+ ret = convert_variable_location(vr_die, pf);
if (ret == 0 && pf->pvar->field) {
ret = convert_variable_fields(vr_die, pf->pvar->var,
pf->pvar->field, &pf->tvar->ref,
@@ -690,19 +718,14 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
ret = convert_variable_type(vr_die, pf->tvar, pf->pvar->type);
/* *expr will be cached in libdw. Don't free it. */
return ret;
-error:
- /* TODO: Support const_value */
- pr_err("Failed to find the location of %s at this address.\n"
- " Perhaps, it has been optimized out.\n", pf->pvar->var);
- return -ENOENT;
}

/* Find a variable in a subprogram die */
static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
{
- Dwarf_Die vr_die;
+ Dwarf_Die vr_die, *scopes;
char buf[32], *ptr;
- int ret;
+ int ret, nscopes;

if (pf->pvar->name)
pf->tvar->name = strdup(pf->pvar->name);
@@ -730,12 +753,26 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
pr_debug("Searching '%s' variable in context.\n",
pf->pvar->var);
/* Search child die for local variables and parameters. */
- if (!die_find_variable(sp_die, pf->pvar->var, &vr_die)) {
+ if (die_find_variable(sp_die, pf->pvar->var, &vr_die))
+ ret = convert_variable(&vr_die, pf);
+ else {
+ /* Search upper class */
+ nscopes = dwarf_getscopes_die(sp_die, &scopes);
+ if (nscopes > 0) {
+ ret = dwarf_getscopevar(scopes, nscopes, pf->pvar->var,
+ 0, NULL, 0, 0, &vr_die);
+ if (ret >= 0)
+ ret = convert_variable(&vr_die, pf);
+ else
+ ret = -ENOENT;
+ free(scopes);
+ } else
+ ret = -ENOENT;
+ }
+ if (ret < 0)
pr_warning("Failed to find '%s' in this function.\n",
pf->pvar->var);
- return -ENOENT;
- }
- return convert_variable(&vr_die, pf);
+ return ret;
}

/* Show a probe point to output buffer */
--
1.6.2.5