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 +83,19 @@ struct FrameDesc {
     static FrameDesc default_clang_frame;
     static FrameDesc no_dwarf_frame;
 
+    // Platform default frame layout for native code when no DWARF info is available.
+    // On aarch64, clang uses FP/LR at [fp-16]/[fp-8] while GCC uses [fp]/[fp+8].
+    // On macOS aarch64 we default to clang since Apple's toolchain is clang-based.
+    // On Linux aarch64 both compilers coexist, so the per-library default is detected
+    // from DWARF via DwarfParser::detectedDefaultFrame() in ElfParser::parseDwarfInfo().
+    static const FrameDesc& default_native_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::default_native_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::default_native_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) {
@@ -212,6 +213,10 @@ void Symbols::parseLibraries(CodeCacheArray* array, bool kernel_symbols) {
             if (!parser.parse()) {
                 Log::warn("Could not parse symbols from %s", path);
             }
+            // Mach-O has no eh_frame_hdr index, so we can't parse per-PC DWARF entries.
+            // Set the platform default frame layout so findFrameDesc() returns the
+            // correct fallback for aarch64 (clang frame convention).
+            cc->setDwarfTable(NULL, 0, FrameDesc::default_native_frame());
             cc->sort();
             if (!array->add(cc)) {
                 delete cc;