From a9af7d7095105a815c848488322f6ffb2e86b10c Mon Sep 17 00:00:00 2001
From: Frederik Carlier <frederik.carlier@keysight.com>
Date: Mon, 18 Nov 2024 21:15:32 +0000
Subject: [PATCH 1/2] msgSend: Return `nil` if the dtable cannot be loaded

Under some circumstances, apparently when two classes with the same name exist in two different modules, the dtable for a class can be null.  This would cause a crash in `msgSend`.

Update `msgSend` to return `nil` instead.
---
 objc_msgSend.x86-64.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/objc_msgSend.x86-64.S b/objc_msgSend.x86-64.S
index 10ecd163..067016a0 100644
--- a/objc_msgSend.x86-64.S
+++ b/objc_msgSend.x86-64.S
@@ -35,6 +35,8 @@
 	mov   (\receiver), %r10               # Load the dtable from the class
 1:	                                      # classLoaded
 	mov   DTABLE_OFFSET(%r10), %r10       # Load the dtable from the class into r10
+	test  %r10, %r10                      # If the dtable is nil
+	jz    4f                              # return nil
 	mov   %rax, -8(%rsp)                  # %rax contains information for variadic calls
 	mov   %rbx, -16(%rsp)                 # On the fast path, spill into the red zone
 	mov   (\sel), %eax                    # Load the selector index into %eax

From 293ea14f9e5f6d65215d7ee35bcdaec2fca625a4 Mon Sep 17 00:00:00 2001
From: Frederik Carlier <frederik.carlier@keysight.com>
Date: Thu, 21 Nov 2024 12:52:51 +0000
Subject: [PATCH 2/2] Add benchmark

---
 benchmarks/CMakeLists.txt   |  6 ++++++
 benchmarks/TestClass.m      | 10 ++++++++++
 benchmarks/objc_msgSend.cpp | 23 +++++++++++++++++++++++
 3 files changed, 39 insertions(+)
 create mode 100644 benchmarks/CMakeLists.txt
 create mode 100644 benchmarks/TestClass.m
 create mode 100644 benchmarks/objc_msgSend.cpp

diff --git a/benchmarks/CMakeLists.txt b/benchmarks/CMakeLists.txt
new file mode 100644
index 00000000..c6c20ac8
--- /dev/null
+++ b/benchmarks/CMakeLists.txt
@@ -0,0 +1,6 @@
+find_package(benchmark REQUIRED)
+
+add_executable(objc_msgSend objc_msgSend.cpp TestClass.m)
+
+target_compile_options(objc_msgSend PRIVATE "-fobjc-runtime=gnustep-2.0")
+target_link_libraries(objc_msgSend benchmark::benchmark objc)
diff --git a/benchmarks/TestClass.m b/benchmarks/TestClass.m
new file mode 100644
index 00000000..d3d85a28
--- /dev/null
+++ b/benchmarks/TestClass.m
@@ -0,0 +1,10 @@
+@interface TestClass
+- (int)answer;
+@end
+
+@implementation TestClass
+- (int)answer
+{
+	return 42;
+}
+@end
diff --git a/benchmarks/objc_msgSend.cpp b/benchmarks/objc_msgSend.cpp
new file mode 100644
index 00000000..5f073168
--- /dev/null
+++ b/benchmarks/objc_msgSend.cpp
@@ -0,0 +1,23 @@
+#include <benchmark/benchmark.h>
+#include "../objc/runtime.h"
+#include <assert.h>
+
+static id testClass;
+static SEL answerSel;
+
+static void objc_msgSendSetup(const benchmark::State& state) {
+  testClass = objc_getClass("TestClass");
+  answerSel = sel_registerName("answer");
+}
+
+static void objc_msgSend(benchmark::State& state) {
+    for (auto _ : state)
+	  {
+      id a = objc_msgSend(testClass, answerSel);
+      assert((uintptr_t)a == 42);
+    }
+  }
+  // Register the function as a benchmark
+  BENCHMARK(objc_msgSend)->Setup(objc_msgSendSetup)->Repetitions(25);
+  
+  BENCHMARK_MAIN();