[ExternalGenericMetadataBuilder] Fix pointer targets, exports, and recursive metadata.

Use exports, not symbols, when emitting a pointer target. Exports are what the linker can actually work with.

When searching for a nearby export to use for a pointer target, accept anything within the same segment, not just the same section. Only segments can be rearranged relative to each other, not sections within a segment, so this is safe and allows for more possible targets.

Disallow pointer targets with no export within the same segment. We attempted to emit a target that's relative to the section starting point in this case, but that didn't work. We'll revisit if it looks useful to do so.

In order to make this work, we resolve the export when writing a pointer instead of when emitting JSON, and make the writePointer functions failable. If writePointer fails, we'll fail to build the metadata and skip it.

Correctly handle the case where the names JSON contains a metadata we already constructed as part of a prior name. Previously we'd emit it twice, now it checks to see if it's already been built and do nothing in that case. Also save errors when a metadata can't be built, so subsequent attempts to build it can fail immediately.

When emitting fixups with ptrauth attributes, use the correct target kind "arm64_auth_ptr".

Fix the VerifyExternalMetadata.swift test not to load an arm64e runtime slice when testing arm64. That's normally fine, but we depend on loading the exact same dylib that we built prespecializations for.

rdar://122968337

Author: mikeash

include/swift/Runtime/GenericMetadataBuilder.h

@@ -296,9 +296,11 @@ class GenericMetadataBuilder {
             patternPointers->resolvePointer(&patternPointers->ptr[i]);
         if (!patternPointer)
           return *patternPointer.getError();
-        data.writePointer(
+        auto writeResult = data.writePointer(
             &metadataExtraData[i + extraDataPattern->OffsetInWords],
             patternPointer->template cast<const StoredPointer>());
+        if (!writeResult)
+          return *writeResult.getError();
       }
     }
 
@@ -310,7 +312,10 @@ class GenericMetadataBuilder {
     if (!valueWitnesses)
       return *valueWitnesses.getError();
     METADATA_BUILDER_LOG("Setting initial value witnesses");
-    data.writePointer(&fullMetadata->ValueWitnesses, *valueWitnesses);
+    auto writeResult =
+        data.writePointer(&fullMetadata->ValueWitnesses, *valueWitnesses);
+    if (!writeResult)
+      return *writeResult.getError();
 
     // Set the metadata kind.
     METADATA_BUILDER_LOG("Setting metadata kind %#x",
@@ -319,7 +324,9 @@ class GenericMetadataBuilder {
 
     // Set the type descriptor.
     METADATA_BUILDER_LOG("Setting descriptor");
-    data.writePointer(&metadata->Description, descriptionBuffer);
+    writeResult = data.writePointer(&metadata->Description, descriptionBuffer);
+    if (!writeResult)
+      return *writeResult.getError();
 
     return {{}};
   }
@@ -353,8 +360,11 @@ class GenericMetadataBuilder {
         header.NumKeyArguments,
         getGenericArgumentOffset(
             descriptionBuffer.template cast<const TypeContextDescriptor>()));
-    for (unsigned i = 0; i < header.NumKeyArguments; i++)
-      data.writePointer(&dst[i], arguments[i]);
+    for (unsigned i = 0; i < header.NumKeyArguments; i++) {
+      auto writeResult = data.writePointer(&dst[i], arguments[i]);
+      if (!writeResult)
+        return *writeResult.getError();
+    }
 
     // TODO: parameter pack support.
 
@@ -495,7 +505,11 @@ class GenericMetadataBuilder {
   auto LOWER_ID##_Buffer = from.resolveFunctionPointer(&from.ptr->LOWER_ID);   \
   if (!LOWER_ID##_Buffer)                                                      \
     return *LOWER_ID##_Buffer.getError();                                      \
-  vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->LOWER_ID, *LOWER_ID##_Buffer);
+  if (auto *error = vwtBuffer                                                  \
+                        .writeFunctionPointer(&vwtBuffer.ptr->LOWER_ID,        \
+                                              *LOWER_ID##_Buffer)              \
+                        .getError())                                           \
+    return *error;
 #define DATA_VALUE_WITNESS(LOWER_ID, UPPER_ID, TYPE)
 #include "swift/ABI/ValueWitness.def"
 
@@ -520,40 +534,56 @@ class GenericMetadataBuilder {
                            (size_t)flags.getAlignmentMask());
       switch (sizeWithAlignmentMask(layout.size, flags.getAlignmentMask(),
                                     hasExtraInhabitants)) {
-      default:
+      default: {
         // For uncommon layouts, use value witnesses that work with an arbitrary
         // size and alignment.
         METADATA_BUILDER_LOG("Uncommon layout case, flags.isInlineStorage=%s",
                              flags.isInlineStorage() ? "true" : "false");
         if (flags.isInlineStorage()) {
           if (!pod_direct_initializeBufferWithCopyOfBuffer)
             return *pod_direct_initializeBufferWithCopyOfBuffer.getError();
-          vwtBuffer.writeFunctionPointer(
+          auto writeResult = vwtBuffer.writeFunctionPointer(
               &vwtBuffer.ptr->initializeBufferWithCopyOfBuffer,
               *pod_direct_initializeBufferWithCopyOfBuffer);
+          if (!writeResult)
+            return *writeResult.getError();
         } else {
           if (!pod_indirect_initializeBufferWithCopyOfBuffer)
             return *pod_indirect_initializeBufferWithCopyOfBuffer.getError();
-          vwtBuffer.writeFunctionPointer(
+          auto writeResult = vwtBuffer.writeFunctionPointer(
               &vwtBuffer.ptr->initializeBufferWithCopyOfBuffer,
               *pod_indirect_initializeBufferWithCopyOfBuffer);
+          if (!writeResult)
+            return *writeResult.getError();
         }
         if (!pod_destroy)
           return *pod_destroy.getError();
         if (!pod_copy)
           return *pod_copy.getError();
-        vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->destroy, *pod_destroy);
-        vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->initializeWithCopy,
-                                       *pod_copy);
-        vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->initializeWithTake,
-                                       *pod_copy);
-        vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->assignWithCopy,
-                                       *pod_copy);
-        vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->assignWithTake,
-                                       *pod_copy);
+        auto writeResult = vwtBuffer.writeFunctionPointer(
+            &vwtBuffer.ptr->destroy, *pod_destroy);
+        if (!writeResult)
+          return *writeResult.getError();
+        writeResult = vwtBuffer.writeFunctionPointer(
+            &vwtBuffer.ptr->initializeWithCopy, *pod_copy);
+        if (!writeResult)
+          return *writeResult.getError();
+        writeResult = vwtBuffer.writeFunctionPointer(
+            &vwtBuffer.ptr->initializeWithTake, *pod_copy);
+        if (!writeResult)
+          return *writeResult.getError();
+        writeResult = vwtBuffer.writeFunctionPointer(
+            &vwtBuffer.ptr->assignWithCopy, *pod_copy);
+        if (!writeResult)
+          return *writeResult.getError();
+        writeResult = vwtBuffer.writeFunctionPointer(
+            &vwtBuffer.ptr->assignWithTake, *pod_copy);
+        if (!writeResult)
+          return *writeResult.getError();
         // getEnumTagSinglePayload and storeEnumTagSinglePayload are not
         // interestingly optimizable based on POD-ness.
         return {{}};
+      }
 
       case sizeWithAlignmentMask(1, 0, 0): {
         METADATA_BUILDER_LOG("case sizeWithAlignmentMask(1, 0, 0)");
@@ -629,8 +659,10 @@ class GenericMetadataBuilder {
       // Use POD value witnesses for operations that do an initializeWithTake.
       if (!pod_copy)
         return *pod_copy.getError();
-      vwtBuffer.writeFunctionPointer(&vwtBuffer.ptr->initializeWithTake,
-                                     *pod_copy);
+      auto writeResult = vwtBuffer.writeFunctionPointer(
+          &vwtBuffer.ptr->initializeWithTake, *pod_copy);
+      if (!writeResult)
+        return *writeResult.getError();
     }
     return {{}};
   }
@@ -761,7 +793,10 @@ class GenericMetadataBuilder {
     auto fptr = oldVWTBuffer->resolveFunctionPointer(&oldVWT->LOWER_ID);       \
     if (!fptr)                                                                 \
       return *fptr.getError();                                                 \
-    newVWTData.writeFunctionPointer(&newVWT->LOWER_ID, *fptr);                 \
+    if (auto *error =                                                          \
+            newVWTData.writeFunctionPointer(&newVWT->LOWER_ID, *fptr)          \
+                .getError())                                                   \
+      return *error;                                                           \
   }
 #include "swift/ABI/ValueWitness.def"
 
@@ -774,9 +809,11 @@ class GenericMetadataBuilder {
     newVWT->extraInhabitantCount = layout.extraInhabitantCount;
     newVWT->flags = layout.flags;
 
-    metadataBuffer.writePointer(
+    auto writeResult = metadataBuffer.writePointer(
         &metadataBuffer.ptr->ValueWitnesses,
         newVWTData.template cast<const ValueWitnessTable>());
+    if (!writeResult)
+      return *writeResult.getError();
     return {{}}; // success
   }