Mark inner map template descriptors in EbpfMapDescriptor

src/io/elf_map_parser.cpp

@@ -295,27 +295,38 @@ ElfGlobalData parse_map_sections(const parse_params_t& parse_params, const ELFIO
 
 ElfGlobalData extract_global_data(const parse_params_t& params, const ELFIO::elfio& reader,
                                   const ELFIO::const_symbol_section_accessor& symbols) {
-    if (reader.sections[".BTF"] && reader.sections[".maps"]) {
-        try {
+    ElfGlobalData global = [&] {
+        if (reader.sections[".BTF"] && reader.sections[".maps"]) {
+            try {
+                return parse_btf_section(params, reader);
+            } catch (const UnmarshalError& e) {
+                // BTF-defined maps can't be decoded; fall back to section-based map descriptors.
+                std::cerr << "BTF map parsing failed, falling back to section-based maps: " << e.what() << std::endl;
+                return parse_map_sections(params, reader, symbols);
+            }
+        }
+        if (std::ranges::any_of(reader.sections, [](const auto& s) { return is_map_section(s->get_name()); })) {
+            return parse_map_sections(params, reader, symbols);
+        }
+        if (reader.sections[".BTF"]) {
             return parse_btf_section(params, reader);
-        } catch (const UnmarshalError& e) {
-            // BTF-defined maps can't be decoded; fall back to section-based map descriptors.
-            std::cerr << "BTF map parsing failed, falling back to section-based maps: " << e.what() << std::endl;
         }
-        return parse_map_sections(params, reader, symbols);
-    }
-
-    const bool has_legacy_maps =
-        std::ranges::any_of(reader.sections, [](const auto& s) { return is_map_section(s->get_name()); });
-    if (has_legacy_maps) {
-        return parse_map_sections(params, reader, symbols);
-    }
+        return create_global_variable_maps(reader);
+    }();
 
-    if (reader.sections[".BTF"]) {
-        return parse_btf_section(params, reader);
+    /// Mark descriptors that serve only as inner map templates.
+    /// At runtime the actual inner map can be any map with matching structure,
+    /// not necessarily the template defined in the ELF.
+    for (const auto& desc : global.map_descriptors) {
+        if (desc.inner_map_fd != DEFAULT_MAP_FD) {
+            for (auto& inner_desc : global.map_descriptors) {
+                if (inner_desc.original_fd == desc.inner_map_fd) {
+                    inner_desc.is_inner_map_template = true;
+                }
+            }
+        }
     }
-
-    return create_global_variable_maps(reader);
+    return global;
 }
 
 void update_line_info(std::vector<RawProgram>& raw_programs, const ELFIO::section* btf_section,

src/spec/type_descriptors.hpp

@@ -30,7 +30,8 @@ struct EbpfMapDescriptor {
     unsigned int value_size;
     unsigned int max_entries;
     int inner_map_fd;
-    std::string name; // Map name from ELF (empty if not available).
+    std::string name;                  // Map name from ELF (empty if not available).
+    bool is_inner_map_template{false}; // True if this descriptor is referenced as an inner map template.
 };
 
 struct EbpfProgramType {