perf probe: Support probing at absolute address

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.

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

v2 -> v3:
  Split bugfix to a separated patch.

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@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1440586666-235233-7-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 163 insertions, 24 deletions

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index eaacb58b9b36..eb5f18b75402 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1204,9 +1204,27 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
 
         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;
@@ -1804,14 +1822,29 @@ 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 ? ":" : "",
@@ -1874,8 +1907,8 @@ 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;
@@ -2331,7 +2364,9 @@ 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;
@@ -2598,6 +2633,98 @@ 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,
@@ -2614,6 +2741,10 @@ 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)
@@ -2784,3 +2915,22 @@ 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 83ee95e9743b..6e7ec68a4aa8 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -59,6 +59,7 @@ 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 */
@@ -156,4 +157,7 @@ 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 7b80f8cb62b9..29c43c0680a8 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);