[PATCH v2 3/4] perf probe: Support probing at absolute address

From: Wang Nan
Date: Wed Aug 26 2015 - 03:41:04 EST

It should be useful to allow 'perf probe' probe at absolute offset of
a target. For example, when (u)probing at a instruction of a shared
object in a embedded system where debuginfo is not avaliable but we
know the offset of that instruction by manually digging.

This patch enables following perf probe command syntax:

# perf probe 0xffffffff811e6615

And

# perf probe /lib/x86_64-linux-gnu/libc-2.19.so 0xeb860

In the above example, we don't need a anchor symbol, so it is possible
to compute absolute addresses using other methods and then use
'perf probe' to create the probing points.

This patch also fix a bug that, when offset is provided but function is
skipped, parse_perf_probe_point() will give function a "" string, so
the checking code at the end of this function is not used. For example:

# perf probe +0x1234
Failed to find symbol in kernel
Error: Failed to add events.

After this patch:

# perf probe +0x1234
Semantic error :Offset requires an entry function.
Error: Command Parse Error.

v1 -> v2:
Drop the leading '+' in cmdline;
Allow uprobing at offset 0x0;
Improve 'perf probe -l' result when uprobe at area without debuginfo.

Test result:

# perf probe 0xffffffff8119d175 %ax
# perf probe sys_write %ax
# perf probe /lib64/libc-2.18.so 0x0 %ax
# perf probe /lib64/libc-2.18.so 0x5 %ax
# perf probe /lib64/libc-2.18.so 0xd8e40 %ax
# perf probe /lib64/libc-2.18.so __write %ax
# perf probe /lib64/libc-2.18.so 0xd8e49 %ax
# cat /sys/kernel/debug/tracing/uprobe_events

p:probe_libc/abs_0 /lib64/libc-2.18.so:0x (null) arg1=%ax
p:probe_libc/abs_5 /lib64/libc-2.18.so:0x0000000000000005 arg1=%ax
p:probe_libc/abs_d8e40 /lib64/libc-2.18.so:0x00000000000d8e40 arg1=%ax
p:probe_libc/__write /lib64/libc-2.18.so:0x00000000000d8e40 arg1=%ax
p:probe_libc/abs_d8e49 /lib64/libc-2.18.so:0x00000000000d8e49 arg1=%ax

# cat /sys/kernel/debug/tracing/kprobe_events

p:probe/abs_ffffffff8119d175 0xffffffff8119d175 arg1=%ax
p:probe/sys_write _text+1692016 arg1=%ax

# perf probe -l

Failed to find debug information for address 5
probe:abs_ffffffff8119d175 (on sys_write+5 with arg1)
probe:sys_write (on sys_write with arg1)
probe_libc:__write (on @unix/syscall-template.S:81 in /lib64/libc-2.18.so with arg1)
probe_libc:abs_0 (on 0x0 in /lib64/libc-2.18.so with arg1)
probe_libc:abs_5 (on 0x5 in /lib64/libc-2.18.so with arg1)
probe_libc:abs_d8e40 (on @unix/syscall-template.S:81 in /lib64/libc-2.18.so with arg1)
probe_libc:abs_d8e49 (on __GI___libc_write+9 in /lib64/libc-2.18.so with arg1)

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
tools/perf/util/probe-event.c | 172 ++++++++++++++++++++++++++++++++++++++---
tools/perf/util/probe-event.h | 4 +
tools/perf/util/probe-finder.c | 21 +----
3 files changed, 170 insertions(+), 27 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 3ce223d..b94a8d7 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1196,15 +1196,37 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
*ptr++ = '\0';
}

- tmp = strdup(arg);
- if (tmp == NULL)
- return -ENOMEM;
+ if (arg[0] == '\0')
+ tmp = NULL;
+ else {
+ tmp = strdup(arg);
+ if (tmp == NULL)
+ return -ENOMEM;
+ }

if (file_spec)
pp->file = tmp;
- else
+ else {
pp->function = tmp;

+ /*
+ * Keep pp->function even if this is absolute address,
+ * so it can mark whether abs_address is valid.
+ * Which make 'perf probe lib.bin 0x0' possible.
+ *
+ * Note that checking length of tmp is not needed
+ * because when we access tmp[1] we know tmp[0] is '0',
+ * so tmp[1] should always valid (but could be '\0').
+ */
+ if (tmp && !strncmp(tmp, "0x", 2)) {
+ pp->abs_address = strtoul(pp->function, &tmp, 0);
+ if (*tmp != '\0') {
+ semantic_error("Invalid absolute address.\n");
+ return -EINVAL;
+ }
+ }
+ }
+
/* Parse other options */
while (ptr) {
arg = ptr;
@@ -1802,14 +1824,29 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
if (len <= 0)
goto error;

- /* Uprobes must have tp->address and tp->module */
- if (tev->uprobes && (!tp->address || !tp->module))
+ /* Uprobes must have tp->module */
+ if (tev->uprobes && !tp->module)
goto error;
+ /*
+ * If tp->address == 0, then this point must be a
+ * absolute address uprobe.
+ * try_to_find_absolute_address() should have made
+ * tp->symbol to "0x0".
+ */
+ if (tev->uprobes && !tp->address) {
+ if (!tp->symbol || strcmp(tp->symbol, "0x0"))
+ goto error;
+ }

/* Use the tp->address for uprobes */
if (tev->uprobes)
ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
tp->module, tp->address);
+ else if (!strncmp(tp->symbol, "0x", 2))
+ /* Absolute address. See try_to_find_absolute_address() */
+ ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
+ tp->module ?: "", tp->module ? ":" : "",
+ tp->address);
else
ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
tp->module ?: "", tp->module ? ":" : "",
@@ -1872,8 +1909,8 @@ out:
}

static int convert_to_perf_probe_point(struct probe_trace_point *tp,
- struct perf_probe_point *pp,
- bool is_kprobe)
+ struct perf_probe_point *pp,
+ bool is_kprobe)
{
char buf[128];
int ret;
@@ -2334,7 +2371,9 @@ static int probe_trace_event__set_name(struct probe_trace_event *tev,
if (pev->event)
event = pev->event;
else
- if (pev->point.function && !strisglob(pev->point.function))
+ if (pev->point.function &&
+ (strncmp(pev->point.function, "0x", 2) != 0) &&
+ !strisglob(pev->point.function))
event = pev->point.function;
else
event = tev->point.realname;
@@ -2604,6 +2643,98 @@ err_out:
goto out;
}

+static int try_to_find_absolute_address(struct perf_probe_event *pev,
+ struct probe_trace_event **tevs)
+{
+ struct perf_probe_point *pp = &pev->point;
+ struct probe_trace_event *tev;
+ struct probe_trace_point *tp;
+ int i, err;
+
+ if (!(pev->point.function && !strncmp(pev->point.function, "0x", 2)))
+ return -EINVAL;
+ if (perf_probe_event_need_dwarf(pev))
+ return -EINVAL;
+
+ /*
+ * This is 'perf probe /lib/libc.so 0xabcd'. Try to probe at
+ * absolute address.
+ *
+ * Only one tev can be generated by this.
+ */
+ *tevs = zalloc(sizeof(*tev));
+ if (!*tevs)
+ return -ENOMEM;
+
+ tev = *tevs;
+ tp = &tev->point;
+
+ /*
+ * Don't use tp->offset, use address directly, because
+ * in synthesize_probe_trace_command() address cannot be
+ * zero.
+ */
+ tp->address = pev->point.abs_address;
+ tp->retprobe = pp->retprobe;
+ tev->uprobes = pev->uprobes;
+
+ err = -ENOMEM;
+ /*
+ * Give it a '0x' leading symbol name.
+ * In __add_probe_trace_events, a NULL symbol is interpreted as
+ * invalud.
+ */
+ if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
+ goto errout;
+
+ /* For kprobe, check range */
+ if ((!tev->uprobes) &&
+ (kprobe_warn_out_range(tev->point.symbol,
+ tev->point.address))) {
+ err = -EACCES;
+ goto errout;
+ }
+
+ if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
+ goto errout;
+
+ if (pev->target) {
+ tp->module = strdup(pev->target);
+ if (!tp->module)
+ goto errout;
+ }
+
+ if (tev->group) {
+ tev->group = strdup(pev->group);
+ if (!tev->group)
+ goto errout;
+ }
+
+ if (pev->event) {
+ tev->event = strdup(pev->event);
+ if (!tev->event)
+ goto errout;
+ }
+
+ tev->nargs = pev->nargs;
+ tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
+ if (!tev->args) {
+ err = -ENOMEM;
+ goto errout;
+ }
+ for (i = 0; i < tev->nargs; i++)
+ copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
+
+ return 1;
+
+errout:
+ if (*tevs) {
+ clear_probe_trace_events(*tevs, 1);
+ *tevs = NULL;
+ }
+ return err;
+}
+
bool __weak arch__prefers_symtab(void) { return false; }

static int convert_to_probe_trace_events(struct perf_probe_event *pev,
@@ -2620,6 +2751,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
}
}

+ ret = try_to_find_absolute_address(pev, tevs);
+ if (ret > 0)
+ return ret;
+
if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
ret = find_probe_trace_events_from_map(pev, tevs);
if (ret > 0)
@@ -2787,3 +2922,22 @@ end:
return ret;
}

+int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
+ struct perf_probe_arg *pvar)
+{
+ tvar->value = strdup(pvar->var);
+ if (tvar->value == NULL)
+ return -ENOMEM;
+ if (pvar->type) {
+ tvar->type = strdup(pvar->type);
+ if (tvar->type == NULL)
+ return -ENOMEM;
+ }
+ if (pvar->name) {
+ tvar->name = strdup(pvar->name);
+ if (tvar->name == NULL)
+ return -ENOMEM;
+ } else
+ tvar->name = NULL;
+ return 0;
+}
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 9c7b99e..de0dd13 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -61,6 +61,7 @@ struct perf_probe_point {
bool retprobe; /* Return probe flag */
char *lazy_line; /* Lazy matching pattern */
unsigned long offset; /* Offset from function entry */
+ unsigned long abs_address; /* Absolute address of the point */
};

/* Perf probe probing argument field chain */
@@ -162,4 +163,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
/* Maximum index number of event-name postfix */
#define MAX_EVENT_INDEX 1024

+int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
+ struct perf_probe_arg *pvar);
+
#endif /*_PROBE_EVENT_H */
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 4b1e074..5ab9cd6 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
char buf[32], *ptr;
int ret = 0;

- if (!is_c_varname(pf->pvar->var)) {
- /* Copy raw parameters */
- pf->tvar->value = strdup(pf->pvar->var);
- if (pf->tvar->value == NULL)
- return -ENOMEM;
- if (pf->pvar->type) {
- pf->tvar->type = strdup(pf->pvar->type);
- if (pf->tvar->type == NULL)
- return -ENOMEM;
- }
- if (pf->pvar->name) {
- pf->tvar->name = strdup(pf->pvar->name);
- if (pf->tvar->name == NULL)
- return -ENOMEM;
- } else
- pf->tvar->name = NULL;
- return 0;
- }
+ /* Copy raw parameters */
+ if (!is_c_varname(pf->pvar->var))
+ return copy_to_probe_trace_arg(pf->tvar, pf->pvar);

if (pf->pvar->name)
pf->tvar->name = strdup(pf->pvar->name);
--
1.8.3.4

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