Re: [PATCH 2/2] perf probe: Support probing at absolute address

From: acme@xxxxxxxxxx
Date: Wed Aug 26 2015 - 09:02:33 EST

Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
>
> On 2015/8/26 8:02, åæéå / HIRAMATUïMASAMI wrote:
> >>From: Wang Nan [mailto:wangnan0@xxxxxxxxxx]
> >>
> >>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
> >Why do we need "+" for the absolute address?
> >It seems that we can do it if we find that the given probe point
> >starts with "0x".
> >
> >Thanks,
>
> I will change 2/2 as you suggection.
>
> However, we can only ensure that in kernel side symbol never leading
> with '0x'. Although I don't think symbol leading with 0x is useful,
> it is still possible for a userspace program compiled and linked by
> a language other than C produces such symbol. '+' helps us separate
> address and function name semantically, make us don't rely on assumption
> on function names. If in future we do meet '0x' symbols, I think we still
> need the '+' syntax back. But we can do it at that time.

Agreed, I also think that using '+' is better, but will not dwell on
this so as to make progress :-)

- Arnaldo

> Thank you.
>
>
> >>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.
> >>
> >>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>
> >>---
> >> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
> >> tools/perf/util/probe-event.h | 3 +
> >> tools/perf/util/probe-finder.c | 21 +-----
> >> 3 files changed, 138 insertions(+), 30 deletions(-)
> >>
> >>diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >>index 6c7e538..59de69a4 100644
> >>--- a/tools/perf/util/probe-event.c
> >>+++ b/tools/perf/util/probe-event.c
> >>@@ -1194,9 +1194,13 @@ 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;
> >>@@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >>- if (pp->offset && !pp->function) {
> >>- semantic_error("Offset requires an entry function.\n");
> >>- return -EINVAL;
> >>- }
> >>-
> >> if (pp->retprobe && !pp->function) {
> >> semantic_error("Return probe requires an entry function.\n");
> >> return -EINVAL;
> >>@@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >>+ if (!pp->function && !pp->offset && !pp->file) {
> >>+ semantic_error("Absolute address should not be zero.\n");
> >>+ return -EINVAL;
> >>+ }
> >>+
> >> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> >> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> >> pp->lazy_line);
> >>@@ -1609,7 +1613,7 @@ error:
> >> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> {
> >> char *buf, *tmp;
> >>- char offs[32] = "", line[32] = "", file[32] = "";
> >>+ char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> >> int ret, len;
> >>
> >> buf = zalloc(MAX_CMDLEN);
> >>@@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> if (ret <= 0)
> >> goto error;
> >> }
> >>+ if (!pp->function) {
> >>+ ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> >>+ if (ret <= 0)
> >>+ goto error;
> >>+ }
> >> if (pp->line) {
> >> ret = e_snprintf(line, 32, ":%d", pp->line);
> >> if (ret <= 0)
> >>@@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> goto error;
> >> }
> >>
> >>- if (pp->function)
> >>- ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> >>- offs, pp->retprobe ? "%return" : "", line,
> >>+ if (pp->function || pp->offset)
> >>+ ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> >>+ pp->function ? : addr,
> >>+ pp->function ? offs : "",
> >>+ pp->retprobe ? "%return" : "", line,
> >> file);
> >> else
> >> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> >>@@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> >> if (tev->uprobes)
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> >> tp->module, tp->address);
> >>+ else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> >>+ /* 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 ? ":" : "",
> >>@@ -2572,6 +2588,87 @@ 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 (perf_probe_event_need_dwarf(pev) || pev->point.function)
> >>+ 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.offset;
> >>+ tp->retprobe = pp->retprobe;
> >>+ tev->uprobes = pev->uprobes;
> >>+
> >>+ err = -ENOMEM;
> >>+ /* Give it a '0x' leading symbol name */
> >>+ 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;
> >>+ 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,
> >>@@ -2588,6 +2685,10 @@ 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)
> >>@@ -2758,3 +2859,22 @@ 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 83ee95e..174a3cf 100644
> >>--- a/tools/perf/util/probe-event.h
> >>+++ b/tools/perf/util/probe-event.h
> >>@@ -156,4 +156,7 @@ 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 7b80f8c..29c43c068 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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