[lldb] Make LLDB resilient against failing dyld introspection APIs

[JDevlieghere]

Summary

Make LLDB resilient against failing dyld introspection APIs: dyld_process_create_for_current_task, dyld_process_snapshot_create_for_process and dyld_process_snapshot_get_shared_cache can all fail and return a nullptr. Instead of having an assert, which doesn't really make sense as we have no control over whether these calls succeed or not, bail out gracefully and use the fallback logic.

rdar://98070414

[aprantl]

Nice.

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

533

should this be auto *?

534

auto *dyld_process = dyld_process_create_for_current_task());
if (!dyld_process)
  return;

?

562

is this redundant?

[JDevlieghere]

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

534

We don't want to return, we want to fall through to the logic below the #endif. I guess I could pull it out into a helper function?

562

No, if this succeeds we're done here.

[JDevlieghere]

Reduce indentation with early returns in a helper function

[aprantl]

Thanks! Evidently I had trouble following the control flow in the earlier revision ;-)

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

 #include "lldb/Host/HostInfo.h"
 #include "lldb/Host/macosx/HostInfoMacOSX.h"
 #include "lldb/Utility/Args.h"
 #include "lldb/Utility/LLDBLog.h"
 #include "lldb/Utility/Log.h"
 #include "lldb/Utility/Timer.h"
 #include "Utility/UuidCompatibility.h"
 
+#include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 
 // C++ Includes
 #include <string>
private:
   UUID m_uuid;
 };
 }
 
 SharedCacheInfo::SharedCacheInfo() {
 #if defined(SDK_HAS_NEW_DYLD_INTROSPECTION_SPIS)
   if (__builtin_available(macOS 12, *)) {
     if (dyld_process_create_for_current_task) {
-      auto dyld_process = dyld_process_create_for_current_task();
-      auto snapshot =
-          dyld_process_snapshot_create_for_process(dyld_process, nullptr);
-      auto shared_cache = dyld_process_snapshot_get_shared_cache(snapshot);
-      assert(dyld_process && snapshot && shared_cache);
-
-      dyld_shared_cache_for_each_image(shared_cache, ^(dyld_image_t image) {
+      if (auto dyld_process = dyld_process_create_for_current_task()) {
+        if (auto snapshot = dyld_process_snapshot_create_for_process(
+                dyld_process, nullptr)) {
+          auto on_exit = llvm::make_scope_exit(
+              [&]() { dyld_process_snapshot_dispose(snapshot); });
+          if (auto shared_cache =
+                  dyld_process_snapshot_get_shared_cache(snapshot)) {
+            dyld_shared_cache_for_each_image(
+                shared_cache, ^(dyld_image_t image) {
                   __block uint64_t minVmAddr = UINT64_MAX;
                   __block uint64_t maxVmAddr = 0;
                   uuid_t uuidStore;
                   __block uuid_t *uuid = &uuidStore;
 
-        dyld_image_for_each_segment_info(image, ^(const char *segmentName,
-                                                  uint64_t vmAddr,
-                                                  uint64_t vmSize, int perm) {
+                  dyld_image_for_each_segment_info(
+                      image, ^(const char *segmentName, uint64_t vmAddr,
                         minVmAddr = std::min(minVmAddr, vmAddr);
                         maxVmAddr = std::max(maxVmAddr, vmAddr + vmSize);
                         dyld_image_copy_uuid(image, uuid);
                       });
                   assert(minVmAddr != UINT_MAX);
                   assert(maxVmAddr != 0);
-        m_images[dyld_image_get_installname(image)] = SharedCacheImageInfo{
+                  m_images[dyld_image_get_installname(image)] =
+                      SharedCacheImageInfo{
                           UUID::fromData(uuid, 16),
-            std::make_shared<DataBufferUnowned>((uint8_t *)minVmAddr,
-                                                maxVmAddr - minVmAddr)};
+                          std::make_shared<DataBufferUnowned>(
+                              (uint8_t *)minVmAddr, maxVmAddr - minVmAddr)};
                 });
-      dyld_process_snapshot_dispose(snapshot);
             return;
           }
         }
+      }
+    }
+  }
 #endif
 
   size_t shared_cache_size;
   uint8_t *shared_cache_start =
       _dyld_get_shared_cache_range(&shared_cache_size);
   uuid_t dsc_uuid;
   _dyld_get_shared_cache_uuid(dsc_uuid);
   m_uuid = UUID::fromData(dsc_uuid);