[lld-macho] Fix crash with DWARF section-relative relocations

lld/MachO/InputFiles.cpp

@@ -411,10 +411,14 @@ void ObjFile::parseSections(ArrayRef<SectionHeader> sectionHeaders) {
       auto *isec = make<ConcatInputSection>(section, data, align);
       if (isDebugSection(isec->getFlags()) &&
           isec->getSegName() == segment_names::dwarf) {
-        // Instead of emitting DWARF sections, we emit STABS symbols to the
-        // object files that contain them. We filter them out early to avoid
-        // parsing their relocations unnecessarily.
+        // Keep debug sections in debugSections for diagnostic purposes
         debugSections.push_back(isec);
+        // Add DWARF sections to subsections so their relocations are processed,
+        // but mark them dead so they aren't emitted (MachO uses STABS, not DWARF).
+        // This fixes crashes with section-relative relocations (e.g., DW_FORM_strp)
+        // while maintaining MachO's traditional STABS-only debug output.
+        isec->live = false;
+        section.subsections.push_back({0, isec});
       } else {
         section.subsections.push_back({0, isec});
       }

lld/test/MachO/dwarf-strp-relocations.s

@@ -0,0 +1,63 @@
+# REQUIRES: x86
+# RUN: rm -rf %t; split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
+# RUN: %lld -dylib %t/test.o -o %t/test.dylib
+# RUN: llvm-objdump --section-headers %t/test.dylib | FileCheck %s
+
+## Test that lld can handle section-relative relocations in DWARF sections,
+## specifically DW_FORM_strp which creates X86_64_RELOC_UNSIGNED relocations
+## to the __debug_str section. This previously caused linker crashes with
+## "malformed relocation" errors on macOS.
+##
+## The test verifies that:
+## 1. The link completes successfully without crashing (key requirement)
+## 2. DWARF sections are processed for relocations but not emitted to output
+##    (MachO traditionally uses STABS, not DWARF, for debug info)
+##
+## Negative checks ensure DWARF sections are NOT in the final binary, preventing
+## regression where they might be accidentally emitted.
+
+# CHECK-NOT: __debug_info
+# CHECK-NOT: __debug_abbrev
+# CHECK-NOT: __debug_str
+
+#--- test.s
+.section __TEXT,__text,regular,pure_instructions
+.globl _main
+_main:
+    movl $42, %eax
+    retq
+
+.section __DWARF,__debug_abbrev,regular,debug
+Labbrev_begin:
+    .byte 1                     ## Abbrev code
+    .byte 17                    ## DW_TAG_compile_unit
+    .byte 1                     ## DW_CHILDREN_yes
+    .byte 37                    ## DW_AT_producer
+    .byte 14                    ## DW_FORM_strp (string table pointer!)
+    .byte 3                     ## DW_AT_name
+    .byte 14                    ## DW_FORM_strp
+    .byte 0                     ## End attributes
+    .byte 0
+    .byte 0                     ## End abbrev table
+
+.section __DWARF,__debug_info,regular,debug
+Linfo_begin:
+    .long Linfo_end - Linfo_begin - 4  ## Length
+    .short 4                    ## DWARF version 4
+    .long 0                     ## Abbrev offset
+    .byte 8                     ## Address size
+    .byte 1                     ## Abbrev code
+    ## These .long directives create section-relative relocations (X86_64_RELOC_UNSIGNED)
+    ## to the __debug_str section. This is the critical test case.
+    .long Lproducer - Ldebug_str  ## DW_AT_producer (section-relative!)
+    .long Lfilename - Ldebug_str  ## DW_AT_name (section-relative!)
+Linfo_end:
+
+.section __DWARF,__debug_str,regular,debug
+Ldebug_str:
+Lproducer:
+    .asciz "Test Producer 1.0"
+Lfilename:
+    .asciz "test.c"