Add 'get_helper_error_msg' utility

This is for additional helpful messaging for specific errors e.g. for when the number of bpf map entries is exceeded. Follow up to: #2809
bpftrace · Jan 10, 2024 · 80dc6ef · 80dc6ef
1 parent 98960e1
commit 80dc6ef
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Showing 5 changed files with 41 additions and 25 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -25,6 +25,8 @@ and this project adheres to
   - [#2830](https://github.com/iovisor/bpftrace/pull/2830)
 - New builtin for getting the number of map elements
   - [#2840](https://github.com/iovisor/bpftrace/pull/2840)
+- Add more helpful error message for map updating
+  - [#2905](https://github.com/iovisor/bpftrace/pull/2905)
 #### Changed
 #### Deprecated
 #### Removed

diff --git a/src/bpftrace.cpp b/src/bpftrace.cpp
@@ -38,12 +38,6 @@
 #include "triggers.h"
 #include "utils.h"
 
-namespace libbpf {
-#define __BPF_NAME_FN(x) #x
-const char *bpf_func_name[] = { __BPF_FUNC_MAPPER(__BPF_NAME_FN) };
-#undef __BPF_NAME_FN
-} // namespace libbpf
-
 namespace bpftrace {
 
 DebugLevel bt_debug = DebugLevel::kNone;
@@ -542,9 +536,7 @@ void perf_event_printer(void *cb_cookie, void *data, int size)
     auto error_id = helpererror->error_id;
     auto return_value = helpererror->return_value;
     auto &info = bpftrace->resources.helper_error_info[error_id];
-    bpftrace->out_->helper_error(libbpf::bpf_func_name[info.func_id],
-                                 return_value,
-                                 info.loc);
+    bpftrace->out_->helper_error(info.func_id, return_value, info.loc);
     return;
   }
   else if (printf_id == asyncactionint(AsyncAction::watchpoint_attach))

diff --git a/src/output.cpp b/src/output.cpp
@@ -4,6 +4,14 @@
 #include "utils.h"
 #include <async_event_types.h>
 
+#include <bpf/libbpf.h>
+
+namespace libbpf {
+#define __BPF_NAME_FN(x) #x
+const char *bpf_func_name[] = { __BPF_FUNC_MAPPER(__BPF_NAME_FN) };
+#undef __BPF_NAME_FN
+} // namespace libbpf
+
 namespace bpftrace {
 
 namespace {
@@ -147,6 +155,20 @@ void Output::lhist_prepare(const std::vector<uint64_t> &values, int min, int max
   }
 }
 
+std::string Output::get_helper_error_msg(int func_id, int retcode) const
+{
+  std::string msg;
+  if (func_id == libbpf::BPF_FUNC_map_update_elem && retcode == -E2BIG)
+  {
+    msg = "Map full; can't update element. Try increasing MAP_KEYS_MAX.";
+  }
+  else
+  {
+    msg = strerror(-retcode);
+  }
+  return msg;
+}
+
 std::string Output::value_to_str(BPFtrace &bpftrace,
                                  const SizedType &type,
                                  std::vector<uint8_t> &value,
@@ -565,17 +587,14 @@ void TextOutput::attached_probes(uint64_t num_probes) const
     out_ << "Attaching " << num_probes << " probes..." << std::endl;
 }
 
-void TextOutput::helper_error(const std::string &helper,
+void TextOutput::helper_error(int func_id,
                               int retcode,
                               const location &loc) const
 {
-  std::stringstream msg;
-  msg << "Failed to " << helper << ": ";
-  if (retcode < 0)
-    msg << strerror(-retcode) << " (" << retcode << ")";
-  else
-    msg << retcode;
-  LOG(WARNING, loc, out_) << msg.str();
+  LOG(WARNING, loc, out_) << get_helper_error_msg(func_id, retcode)
+                          << "\nAdditional Info - helper: "
+                          << libbpf::bpf_func_name[func_id]
+                          << ", retcode: " << retcode;
 }
 
 std::string TextOutput::field_to_str(const std::string &name,
@@ -855,13 +874,15 @@ void JsonOutput::attached_probes(uint64_t num_probes) const
   message(MessageType::attached_probes, "probes", num_probes);
 }
 
-void JsonOutput::helper_error(const std::string &helper,
+void JsonOutput::helper_error(int func_id,
                               int retcode,
                               const location &loc) const
 {
-  out_ << "{\"type\": \"helper_error\", \"helper\": \"" << helper
-       << "\", \"retcode\": " << retcode << ", \"line\": " << loc.begin.line
-       << ", \"col\": " << loc.begin.column << "}" << std::endl;
+  out_ << "{\"type\": \"helper_error\", \"msg\": \""
+       << get_helper_error_msg(func_id, retcode) << "\", \"helper\": \""
+       << libbpf::bpf_func_name[func_id] << "\", \"retcode\": " << retcode
+       << ", \"line\": " << loc.begin.line << ", \"col\": " << loc.begin.column
+       << "}" << std::endl;
 }
 
 std::string JsonOutput::field_to_str(const std::string &name,

diff --git a/src/output.h b/src/output.h
@@ -77,7 +77,7 @@ class Output
   virtual void message(MessageType type, const std::string& msg, bool nl = true) const = 0;
   virtual void lost_events(uint64_t lost) const = 0;
   virtual void attached_probes(uint64_t num_probes) const = 0;
-  virtual void helper_error(const std::string &helper,
+  virtual void helper_error(int func_id,
                             int retcode,
                             const location &loc) const = 0;
 
@@ -86,6 +86,7 @@ class Output
   std::ostream &err_;
   void hist_prepare(const std::vector<uint64_t> &values, int &min_index, int &max_index, int &max_value) const;
   void lhist_prepare(const std::vector<uint64_t> &values, int min, int max, int step, int &max_index, int &max_value, int &buckets, int &start_value, int &end_value) const;
+  std::string get_helper_error_msg(int func_id, int retcode) const;
   // Convert a log2 histogram into string
   virtual std::string hist_to_str(const std::vector<uint64_t> &values,
                                   uint32_t div,
@@ -194,7 +195,7 @@ class TextOutput : public Output {
   void message(MessageType type, const std::string& msg, bool nl = true) const override;
   void lost_events(uint64_t lost) const override;
   void attached_probes(uint64_t num_probes) const override;
-  void helper_error(const std::string &helper,
+  void helper_error(int func_id,
                     int retcode,
                     const location &loc) const override;
 
@@ -249,7 +250,7 @@ class JsonOutput : public Output {
   void message(MessageType type, const std::string& field, uint64_t value) const;
   void lost_events(uint64_t lost) const override;
   void attached_probes(uint64_t num_probes) const override;
-  void helper_error(const std::string &helper,
+  void helper_error(int func_id,
                     int retcode,
                     const location &loc) const override;
 

diff --git a/tests/runtime/json-output b/tests/runtime/json-output
@@ -167,7 +167,7 @@ TIMEOUT 1
 
 NAME helper_error
 RUN {{BPFTRACE}} -kk -q -f json -e 'struct foo {int a;}; BEGIN { $tmp = ((struct foo*) 0)->a; exit(); }'
-EXPECT {"type": "helper_error", "helper": "probe_read", "retcode": -14, "line": 1, "col": 37}
+EXPECT {"type": "helper_error", "msg": "Bad address", "helper": "probe_read", "retcode": -14, "line": 1, "col": 37}
 TIMEOUT 1
 
 NAME cgroup_path