Set clang frame layout as default for macOS aarch64

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/src/main/cpp/dwarf.h

@@ -83,6 +83,17 @@ struct FrameDesc {
     static FrameDesc default_clang_frame;
     static FrameDesc no_dwarf_frame;
 
+    // Best-guess fallback frame layout when a PC doesn't map to any known library.
+    // Per-library detection overrides this: on macOS via __eh_frame section presence,
+    // on Linux via DwarfParser::detectedDefaultFrame().
+    static const FrameDesc& fallback_default_frame() {
+#if defined(__APPLE__) && defined(__aarch64__)
+        return default_clang_frame;
+#else
+        return default_frame;
+#endif
+    }
+
     static int comparator(const void* p1, const void* p2) {
         FrameDesc* fd1 = (FrameDesc*)p1;
         FrameDesc* fd2 = (FrameDesc*)p2;

ddprof-lib/src/main/cpp/stackWalker.cpp

@@ -158,11 +158,7 @@ int StackWalker::walkDwarf(void* ucontext, const void** callchain, int max_depth
 
         uintptr_t prev_sp = sp;
         CodeCache* cc = profiler->findLibraryByAddress(pc);
-#if defined(__APPLE__) && defined(__aarch64__)
-        FrameDesc f = cc != NULL ? cc->findFrameDesc(pc) : FrameDesc::default_clang_frame;
-#else
-        FrameDesc f = cc != NULL ? cc->findFrameDesc(pc) : FrameDesc::default_frame;
-#endif
+        FrameDesc f = cc != NULL ? cc->findFrameDesc(pc) : FrameDesc::fallback_default_frame();
 
         u8 cfa_reg = (u8)f.cfa;
         int cfa_off = f.cfa >> 8;
@@ -698,11 +694,7 @@ __attribute__((no_sanitize("address"))) int StackWalker::walkVM(void* ucontext,
         dwarf_unwind:
         uintptr_t prev_sp = sp;
         CodeCache* cc = profiler->findLibraryByAddress(pc);
-#if defined(__APPLE__) && defined(__aarch64__)
-        FrameDesc f = cc != NULL ? cc->findFrameDesc(pc) : FrameDesc::default_clang_frame;
-#else
-        FrameDesc f = cc != NULL ? cc->findFrameDesc(pc) : FrameDesc::default_frame;
-#endif
+        FrameDesc f = cc != NULL ? cc->findFrameDesc(pc) : FrameDesc::fallback_default_frame();
 
         u8 cfa_reg = (u8)f.cfa;
         int cfa_off = f.cfa >> 8;

ddprof-lib/src/main/cpp/symbols_linux.cpp

@@ -604,6 +604,9 @@ void ElfParser::parseDwarfInfo() {
     ElfProgramHeader* eh_frame_hdr = findProgramHeader(PT_GNU_EH_FRAME);
     if (eh_frame_hdr != NULL) {
         if (eh_frame_hdr->p_vaddr != 0) {
+            // Parse per-PC frame descriptions and detect per-library default frame layout.
+            // On aarch64 this distinguishes GCC (LINKED_FRAME_SIZE=0) from clang
+            // (LINKED_FRAME_CLANG_SIZE=16) conventions for each shared library.
             DwarfParser dwarf(_cc->name(), _base, at(eh_frame_hdr));
             _cc->setDwarfTable(dwarf.table(), dwarf.count(), dwarf.detectedDefaultFrame());
         } else if (strcmp(_cc->name(), "[vdso]") == 0) {

ddprof-lib/src/main/cpp/symbols_macos.cpp

@@ -12,6 +12,7 @@
 #include <mach-o/loader.h>
 #include <mach-o/nlist.h>
 #include "symbols.h"
+#include "dwarf.h"
 #include "log.h"
 
 UnloadProtection::UnloadProtection(const CodeCache *cc) {
@@ -138,13 +139,15 @@ class MachOParser {
         const symtab_command* symtab = NULL;
         const dysymtab_command* dysymtab = NULL;
         const section_64* stubs_section = NULL;
+        bool has_eh_frame = false;
 
         for (uint32_t i = 0; i < header->ncmds; i++) {
             if (lc->cmd == LC_SEGMENT_64) {
                 const segment_command_64* sc = (const segment_command_64*)lc;
                 if (strcmp(sc->segname, "__TEXT") == 0) {
                     _cc->updateBounds(_image_base, add(_image_base, sc->vmsize));
                     stubs_section = findSection(sc, "__stubs");
+                    has_eh_frame = findSection(sc, "__eh_frame") != NULL;
                 } else if (strcmp(sc->segname, "__LINKEDIT") == 0) {
                     link_base = _vmaddr_slide + sc->vmaddr - sc->fileoff;
                 } else if (strcmp(sc->segname, "__DATA") == 0 || strcmp(sc->segname, "__DATA_CONST") == 0) {
@@ -168,6 +171,12 @@ class MachOParser {
             }
         }
 
+        // GCC emits __eh_frame (DWARF CFI); clang emits __unwind_info (compact unwind).
+        // On aarch64, GCC and clang use different frame layouts, so detecting the
+        // compiler matters. On x86_64 both use the same layout (no-op distinction).
+        const FrameDesc& frame = has_eh_frame ? FrameDesc::default_frame : FrameDesc::fallback_default_frame();
+        _cc->setDwarfTable(NULL, 0, frame);
+
         return true;
     }
 };