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 7, 2024 · 610b164 · 610b164
1 parent c1d338d
commit 610b164
Show file tree

Hide file tree

Showing 3 changed files with 30 additions and 17 deletions.
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;
@@ -541,9 +535,7 @@ 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 +155,16 @@ 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 = strerror(-retcode);
+  if (func_id == libbpf::BPF_FUNC_map_update_elem && retcode == -E2BIG)
+  {
+    msg.append(" (trying increasing MAP_KEYS_MAX)");
+  }
+  return msg;
+}
+
 std::string Output::value_to_str(BPFtrace &bpftrace,
                                  const SizedType &type,
                                  std::vector<uint8_t> &value,
@@ -565,14 +583,14 @@ 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 << ": ";
+  msg << "Failed to " << libbpf::bpf_func_name[func_id] << ": ";
   if (retcode < 0)
-    msg << strerror(-retcode) << " (" << retcode << ")";
+    msg << get_helper_error_msg(func_id, retcode) << " (" << retcode << ")";
   else
     msg << retcode;
   LOG(WARNING, loc, out_) << msg.str();
@@ -855,11 +873,13 @@ 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
+  out_ << "{\"type\": \"helper_error\", \"helper\": \""
+       << libbpf::bpf_func_name[func_id] << "\", \"msg\": \""
+       << get_helper_error_msg(func_id, retcode)
        << "\", \"retcode\": " << retcode << ", \"line\": " << loc.begin.line
        << ", \"col\": " << loc.begin.column << "}" << std::endl;
 }

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;