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Subject[PATCH v3 9/9] perf probe: Support SDT markers having reference counter (semaphore)
Date
From: Ravi Bangoria <ravi.bangoria@linux.ibm.com>

With this, perf buildid-cache will save SDT markers with reference
counter in probe cache. Perf probe will be able to probe markers
having reference counter. Ex,

# readelf -n /tmp/tick | grep -A1 loop2
Name: loop2
... Semaphore: 0x0000000010020036

# ./perf buildid-cache --add /tmp/tick
# ./perf probe sdt_tick:loop2
# ./perf stat -e sdt_tick:loop2 /tmp/tick
hi: 0
hi: 1
hi: 2
^C
Performance counter stats for '/tmp/tick':
3 sdt_tick:loop2
2.561851452 seconds time elapsed

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
---
tools/perf/util/probe-event.c | 39 ++++++++++++++++++++++++++++++++----
tools/perf/util/probe-event.h | 1 +
tools/perf/util/probe-file.c | 34 ++++++++++++++++++++++++++------
tools/perf/util/probe-file.h | 1 +
tools/perf/util/symbol-elf.c | 46 ++++++++++++++++++++++++++++++++-----------
tools/perf/util/symbol.h | 7 +++++++
6 files changed, 106 insertions(+), 22 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index e1dbc98..9b9c26e 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1832,6 +1832,12 @@ int parse_probe_trace_command(const char *cmd, struct probe_trace_event *tev)
tp->offset = strtoul(fmt2_str, NULL, 10);
}

+ if (tev->uprobes) {
+ fmt2_str = strchr(p, '(');
+ if (fmt2_str)
+ tp->ref_ctr_offset = strtoul(fmt2_str + 1, NULL, 0);
+ }
+
tev->nargs = argc - 2;
tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
if (tev->args == NULL) {
@@ -2025,6 +2031,22 @@ static int synthesize_probe_trace_arg(struct probe_trace_arg *arg,
return err;
}

+static int
+synthesize_uprobe_trace_def(struct probe_trace_event *tev, struct strbuf *buf)
+{
+ struct probe_trace_point *tp = &tev->point;
+ int err;
+
+ err = strbuf_addf(buf, "%s:0x%lx", tp->module, tp->address);
+
+ if (err >= 0 && tp->ref_ctr_offset) {
+ if (!uprobe_ref_ctr_is_supported())
+ return -1;
+ err = strbuf_addf(buf, "(0x%lx)", tp->ref_ctr_offset);
+ }
+ return err >= 0 ? 0 : -1;
+}
+
char *synthesize_probe_trace_command(struct probe_trace_event *tev)
{
struct probe_trace_point *tp = &tev->point;
@@ -2054,15 +2076,17 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
}

/* Use the tp->address for uprobes */
- if (tev->uprobes)
- err = strbuf_addf(&buf, "%s:0x%lx", tp->module, tp->address);
- else if (!strncmp(tp->symbol, "0x", 2))
+ if (tev->uprobes) {
+ err = synthesize_uprobe_trace_def(tev, &buf);
+ } else if (!strncmp(tp->symbol, "0x", 2)) {
/* Absolute address. See try_to_find_absolute_address() */
err = strbuf_addf(&buf, "%s%s0x%lx", tp->module ?: "",
tp->module ? ":" : "", tp->address);
- else
+ } else {
err = strbuf_addf(&buf, "%s%s%s+%lu", tp->module ?: "",
tp->module ? ":" : "", tp->symbol, tp->offset);
+ }
+
if (err)
goto error;

@@ -2646,6 +2670,13 @@ static void warn_uprobe_event_compat(struct probe_trace_event *tev)
{
int i;
char *buf = synthesize_probe_trace_command(tev);
+ struct probe_trace_point *tp = &tev->point;
+
+ if (tp->ref_ctr_offset && !uprobe_ref_ctr_is_supported()) {
+ pr_warning("A semaphore is associated with %s:%s and "
+ "seems your kernel doesn't support it.\n",
+ tev->group, tev->event);
+ }

/* Old uprobe event doesn't support memory dereference */
if (!tev->uprobes || tev->nargs == 0 || !buf)
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 45b14f0..15a98c3 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -27,6 +27,7 @@ struct probe_trace_point {
char *symbol; /* Base symbol */
char *module; /* Module name */
unsigned long offset; /* Offset from symbol */
+ unsigned long ref_ctr_offset; /* SDT reference counter offset */
unsigned long address; /* Actual address of the trace point */
bool retprobe; /* Return probe flag */
};
diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
index 4ae1123..a17ba6a 100644
--- a/tools/perf/util/probe-file.c
+++ b/tools/perf/util/probe-file.c
@@ -697,8 +697,16 @@ int probe_cache__add_entry(struct probe_cache *pcache,
#ifdef HAVE_GELF_GETNOTE_SUPPORT
static unsigned long long sdt_note__get_addr(struct sdt_note *note)
{
- return note->bit32 ? (unsigned long long)note->addr.a32[0]
- : (unsigned long long)note->addr.a64[0];
+ return note->bit32 ?
+ (unsigned long long)note->addr.a32[SDT_NOTE_IDX_LOC] :
+ (unsigned long long)note->addr.a64[SDT_NOTE_IDX_LOC];
+}
+
+static unsigned long long sdt_note__get_ref_ctr_offset(struct sdt_note *note)
+{
+ return note->bit32 ?
+ (unsigned long long)note->addr.a32[SDT_NOTE_IDX_REFCTR] :
+ (unsigned long long)note->addr.a64[SDT_NOTE_IDX_REFCTR];
}

static const char * const type_to_suffix[] = {
@@ -776,14 +784,21 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
{
struct strbuf buf;
char *ret = NULL, **args;
- int i, args_count;
+ int i, args_count, err;
+ unsigned long long ref_ctr_offset;

if (strbuf_init(&buf, 32) < 0)
return NULL;

- if (strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
- sdtgrp, note->name, pathname,
- sdt_note__get_addr(note)) < 0)
+ err = strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
+ sdtgrp, note->name, pathname,
+ sdt_note__get_addr(note));
+
+ ref_ctr_offset = sdt_note__get_ref_ctr_offset(note);
+ if (ref_ctr_offset && err >= 0)
+ err = strbuf_addf(&buf, "(0x%llx)", ref_ctr_offset);
+
+ if (err < 0)
goto error;

if (!note->args)
@@ -999,6 +1014,7 @@ int probe_cache__show_all_caches(struct strfilter *filter)
enum ftrace_readme {
FTRACE_README_PROBE_TYPE_X = 0,
FTRACE_README_KRETPROBE_OFFSET,
+ FTRACE_README_UPROBE_REF_CTR,
FTRACE_README_END,
};

@@ -1010,6 +1026,7 @@ enum ftrace_readme {
[idx] = {.pattern = pat, .avail = false}
DEFINE_TYPE(FTRACE_README_PROBE_TYPE_X, "*type: * x8/16/32/64,*"),
DEFINE_TYPE(FTRACE_README_KRETPROBE_OFFSET, "*place (kretprobe): *"),
+ DEFINE_TYPE(FTRACE_README_UPROBE_REF_CTR, "*ref_ctr_offset*"),
};

static bool scan_ftrace_readme(enum ftrace_readme type)
@@ -1065,3 +1082,8 @@ bool kretprobe_offset_is_supported(void)
{
return scan_ftrace_readme(FTRACE_README_KRETPROBE_OFFSET);
}
+
+bool uprobe_ref_ctr_is_supported(void)
+{
+ return scan_ftrace_readme(FTRACE_README_UPROBE_REF_CTR);
+}
diff --git a/tools/perf/util/probe-file.h b/tools/perf/util/probe-file.h
index 63f29b1..2a24918 100644
--- a/tools/perf/util/probe-file.h
+++ b/tools/perf/util/probe-file.h
@@ -69,6 +69,7 @@ struct probe_cache_entry *probe_cache__find_by_name(struct probe_cache *pcache,
int probe_cache__show_all_caches(struct strfilter *filter);
bool probe_type_is_available(enum probe_type type);
bool kretprobe_offset_is_supported(void);
+bool uprobe_ref_ctr_is_supported(void);
#else /* ! HAVE_LIBELF_SUPPORT */
static inline struct probe_cache *probe_cache__new(const char *tgt __maybe_unused, struct nsinfo *nsi __maybe_unused)
{
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 2de7705..45b7dba 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1803,6 +1803,34 @@ void kcore_extract__delete(struct kcore_extract *kce)
}

#ifdef HAVE_GELF_GETNOTE_SUPPORT
+
+static void sdt_adjust_loc(struct sdt_note *tmp, GElf_Addr base_off)
+{
+ if (!base_off)
+ return;
+
+ if (tmp->bit32)
+ tmp->addr.a32[SDT_NOTE_IDX_LOC] =
+ tmp->addr.a32[SDT_NOTE_IDX_LOC] + base_off -
+ tmp->addr.a32[SDT_NOTE_IDX_BASE];
+ else
+ tmp->addr.a64[SDT_NOTE_IDX_LOC] =
+ tmp->addr.a64[SDT_NOTE_IDX_LOC] + base_off -
+ tmp->addr.a64[SDT_NOTE_IDX_BASE];
+}
+
+static void sdt_adjust_refctr(struct sdt_note *tmp, GElf_Addr base_addr,
+ GElf_Addr base_off)
+{
+ if (!base_off)
+ return;
+
+ if (tmp->bit32)
+ tmp->addr.a32[SDT_NOTE_IDX_REFCTR] -= (base_addr - base_off);
+ else
+ tmp->addr.a64[SDT_NOTE_IDX_REFCTR] -= (base_addr - base_off);
+}
+
/**
* populate_sdt_note : Parse raw data and identify SDT note
* @elf: elf of the opened file
@@ -1820,7 +1848,6 @@ static int populate_sdt_note(Elf **elf, const char *data, size_t len,
const char *provider, *name, *args;
struct sdt_note *tmp = NULL;
GElf_Ehdr ehdr;
- GElf_Addr base_off = 0;
GElf_Shdr shdr;
int ret = -EINVAL;

@@ -1916,17 +1943,12 @@ static int populate_sdt_note(Elf **elf, const char *data, size_t len,
* base address in the description of the SDT note. If its different,
* then accordingly, adjust the note location.
*/
- if (elf_section_by_name(*elf, &ehdr, &shdr, SDT_BASE_SCN, NULL)) {
- base_off = shdr.sh_offset;
- if (base_off) {
- if (tmp->bit32)
- tmp->addr.a32[0] = tmp->addr.a32[0] + base_off -
- tmp->addr.a32[1];
- else
- tmp->addr.a64[0] = tmp->addr.a64[0] + base_off -
- tmp->addr.a64[1];
- }
- }
+ if (elf_section_by_name(*elf, &ehdr, &shdr, SDT_BASE_SCN, NULL))
+ sdt_adjust_loc(tmp, shdr.sh_offset);
+
+ /* Adjust reference counter offset */
+ if (elf_section_by_name(*elf, &ehdr, &shdr, SDT_PROBES_SCN, NULL))
+ sdt_adjust_refctr(tmp, shdr.sh_addr, shdr.sh_offset);

list_add_tail(&tmp->note_list, sdt_notes);
return 0;
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 70c16741..aa095bf 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -384,12 +384,19 @@ struct sdt_note {
int cleanup_sdt_note_list(struct list_head *sdt_notes);
int sdt_notes__get_count(struct list_head *start);

+#define SDT_PROBES_SCN ".probes"
#define SDT_BASE_SCN ".stapsdt.base"
#define SDT_NOTE_SCN ".note.stapsdt"
#define SDT_NOTE_TYPE 3
#define SDT_NOTE_NAME "stapsdt"
#define NR_ADDR 3

+enum {
+ SDT_NOTE_IDX_LOC = 0,
+ SDT_NOTE_IDX_BASE,
+ SDT_NOTE_IDX_REFCTR,
+};
+
struct mem_info *mem_info__new(void);
struct mem_info *mem_info__get(struct mem_info *mi);
void mem_info__put(struct mem_info *mi);
--
1.8.3.1
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