userspace-probe: Print error for unsupported instrumentation mode

This patch adds an error message printed when the user tries to place an
userspace-probe using unsupported probe location descriptions.
Hopefully, this will help users understand why their command failed.

Here are examples of unsupported uses of an address location:
* "elf:/path/to/binary:0x400430"
* "elf:/path/to/binary:4194364"

Here are examples of unsupported uses of offset from symbol location:
* "elf:/path/to/binary:my_symbol+0x323"
* "elf:/path/to/binary:my_symbol+43"

I expect users to try using the address locations and offset from symbol
locations for ELF instrumentation location because those methods are
available with the --probe option used to instrument the kernel.

Supporting those location descriptions in the future would require
the validation that the address or the offset from a symbol is indeed at
the boundary of an instruction.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng/commands/enable_events.c b/src/bin/lttng/commands/enable_events.c
index 23dff2038f3ef17b1090ba63e186771f9ee5d60a..41be3a5a03fbd5476732657e35b46769b347c02d 100644 (file)
--- a/src/bin/lttng/commands/enable_events.c
+++ b/src/bin/lttng/commands/enable_events.c
@@ -290,6 +290,67 @@ end:
        return ret;
 }
 
+/*
+ * Check if the symbol field passed by the user is in fact an address or an
+ * offset from a symbol. Those two instrumentation types are not supported yet.
+ * It's expected to be a common mistake because of the existing --probe option
+ * that does support these formats.
+ *
+ * Here are examples of these unsupported formats for the --userspace-probe
+ * option:
+ * elf:/path/to/binary:0x400430
+ * elf:/path/to/binary:4194364
+ * elf:/path/to/binary:my_symbol+0x323
+ * elf:/path/to/binary:my_symbol+43
+ */
+static int warn_userspace_probe_syntax(const char *symbol)
+{
+       unsigned long addr = 0;
+       size_t offset = 0;
+       int ret;
+
+       /* Check if the symbol field is an hex address. */
+       ret = sscanf(symbol, "0x%lx", &addr);
+       if (ret > 0) {
+               /* If there is a match, print a warning and return an error. */
+               ERR("Userspace probe on address not supported yet.");
+               ret = CMD_UNSUPPORTED;
+               goto error;
+       }
+
+       /* Check if the symbol field is an decimal address. */
+       ret = sscanf(symbol, "%lu", &addr);
+       if (ret > 0) {
+               /* If there is a match, print a warning and return an error. */
+               ERR("Userspace probe on address not supported yet.");
+               ret = CMD_UNSUPPORTED;
+               goto error;
+       }
+
+       /* Check if the symbol field is symbol+hex_offset. */
+       ret = sscanf(symbol, "%*[^+]+0x%lx", &offset);
+       if (ret > 0) {
+               /* If there is a match, print a warning and return an error. */
+               ERR("Userspace probe on symbol+offset not supported yet.");
+               ret = CMD_UNSUPPORTED;
+               goto error;
+       }
+
+       /* Check if the symbol field is symbol+decimal_offset. */
+       ret = sscanf(symbol, "%*[^+]+%lu", &offset);
+       if (ret > 0) {
+               /* If there is a match, print a warning and return an error. */
+               ERR("Userspace probe on symbol+offset not supported yet.");
+               ret = CMD_UNSUPPORTED;
+               goto error;
+       }
+
+       ret = 0;
+
+error:
+       return ret;
+}
+
 /*
  * Parse userspace probe options
  * Set the userspace probe fields in the lttng_event struct and set the
@@ -389,7 +450,7 @@ static int parse_userspace_probe_opts(struct lttng_event *ev, char *opt)
        /* strutils_unescape_string allocates a new char *. */
        unescaped_target_path = strutils_unescape_string(target_path, 0);
        if (!unescaped_target_path) {
-               ret = -LTTNG_ERR_INVALID;
+               ret = CMD_ERROR;
                goto end_destroy_lookup_method;
        }
 
@@ -437,6 +498,14 @@ static int parse_userspace_probe_opts(struct lttng_event *ev, char *opt)
 
        switch (lttng_userspace_probe_location_lookup_method_get_type(lookup_method)) {
        case LTTNG_USERSPACE_PROBE_LOCATION_LOOKUP_METHOD_TYPE_FUNCTION_ELF:
+               /*
+                * Check for common mistakes in userspace probe description syntax.
+                */
+               ret = warn_userspace_probe_syntax(symbol_name);
+               if (ret) {
+                       goto end_destroy_lookup_method;
+               }
+
                probe_location = lttng_userspace_probe_location_function_create(
                                real_target_path, symbol_name, lookup_method);
                if (!probe_location) {
@@ -1296,8 +1365,19 @@ static int enable_events(char *session_name)
                        case LTTNG_EVENT_USERSPACE_PROBE:
                                ret = parse_userspace_probe_opts(ev, opt_userspace_probe);
                                if (ret) {
-                                       ERR("Unable to parse userspace probe options");
-                                       ret = CMD_ERROR;
+                                       switch (ret) {
+                                       case CMD_UNSUPPORTED:
+                                               /*
+                                                * Error message describing
+                                                * what is not supported was
+                                                * printed in the function.
+                                                */
+                                               break;
+                                       case CMD_ERROR:
+                                       default:
+                                               ERR("Unable to parse userspace probe options");
+                                               break;
+                                       }
                                        goto error;
                                }
                                break;