elf_reader: don't panic if ex.extInfo is nil

When the ELF has no BTF, ex.extInfo will be nil. This was overlooked in a
recent refactor.

Signed-off-by: Timo Beckers <timo@isovalent.com>

Author: ti-mo

btf/ext_info.go

@@ -21,6 +21,17 @@ type ExtInfos struct {
 	CORERelos map[string]CORERelocationOffsets
 }
 
+// Section returns the FuncOffsets, LineOffsets and CORERelocationOffsets for
+// the given section name. Returns all nils if ExtInfos is nil, or individual
+// nils if there is no metadata of that type for the section.
+func (ei *ExtInfos) Section(name string) (FuncOffsets, LineOffsets, CORERelocationOffsets) {
+	if ei == nil {
+		return nil, nil, nil
+	}
+
+	return ei.Funcs[name], ei.Lines[name], ei.CORERelos[name]
+}
+
 // loadExtInfosFromELF parses ext infos from the .BTF.ext section in an ELF.
 //
 // Returns an error wrapping ErrNotFound if no ext infos are present.

elf_reader.go

@@ -439,9 +439,7 @@ func (ec *elfCode) loadFunctions(sec *elfSection) (map[string]asm.Instructions,
 
 	// Pull out ExtInfos once per section to avoid map lookups on every
 	// instruction.
-	fo := ec.extInfo.Funcs[sec.Name]
-	lo := ec.extInfo.Lines[sec.Name]
-	ro := ec.extInfo.CORERelos[sec.Name]
+	fo, lo, ro := ec.extInfo.Section(sec.Name)
 
 	// Raw instruction count since start of the section. ExtInfos point at raw
 	// insn offsets and ignore the gaps between symbols in case of linked objects.