From 793f4723aaaa832e174dcbe23f74de529ec03fd2 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston@google.com>
Date: Thu, 28 Aug 2025 22:19:35 +0000
Subject: [PATCH 1/3] [msan] Add test for deferencing zero-sized malloc/calloc

MSan fails to catch this, because 0-byte allocations are converted into
1-byte allocations.

Bug originally reported by dvyukov
---
 compiler-rt/test/msan/zero_alloc.cpp | 37 ++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 compiler-rt/test/msan/zero_alloc.cpp

diff --git a/compiler-rt/test/msan/zero_alloc.cpp b/compiler-rt/test/msan/zero_alloc.cpp
new file mode 100644
index 0000000000000..4b60c161efb36
--- /dev/null
+++ b/compiler-rt/test/msan/zero_alloc.cpp
@@ -0,0 +1,37 @@
+// RUN: %clang_msan -Wno-alloc-size -fsanitize-recover=memory %s -o %t && not %run %t 2>&1 | FileCheck %s
+
+// XFAIL: *
+
+#include <malloc.h>
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+  {
+     char* p1 = (char*)calloc(1, 0);
+     printf ("p1 is %p\n", p1);
+     printf ("Content of p1 is: %d\n", *p1);
+     // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+     // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
+     free(p1);
+  }
+
+  {
+     char* p2 = (char*)calloc(0, 1);
+     printf ("p2 is %p\n", p2);
+     printf ("Content of p2 is: %d\n", *p2);
+     // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+     // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
+     free(p2);
+  }
+
+  {
+     char* p3 = (char*)malloc(0);
+     printf ("p3 is %p\n", p3);
+     printf ("Content of p2 is: %d\n", *p3);
+     // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+     // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
+     free(p3);
+  }
+
+  return 0;
+}

From 6276e55954d2c84cd68e68e9819b3216acc9be7b Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston@google.com>
Date: Thu, 28 Aug 2025 22:22:23 +0000
Subject: [PATCH 2/3] clang-format

---
 compiler-rt/test/msan/zero_alloc.cpp | 36 ++++++++++++++--------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/compiler-rt/test/msan/zero_alloc.cpp b/compiler-rt/test/msan/zero_alloc.cpp
index 4b60c161efb36..6a3ce26e256b7 100644
--- a/compiler-rt/test/msan/zero_alloc.cpp
+++ b/compiler-rt/test/msan/zero_alloc.cpp
@@ -7,30 +7,30 @@
 
 int main(int argc, char **argv) {
   {
-     char* p1 = (char*)calloc(1, 0);
-     printf ("p1 is %p\n", p1);
-     printf ("Content of p1 is: %d\n", *p1);
-     // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
-     // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
-     free(p1);
+    char *p1 = (char *)calloc(1, 0);
+    printf("p1 is %p\n", p1);
+    printf("Content of p1 is: %d\n", *p1);
+    // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+    // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
+    free(p1);
   }
 
   {
-     char* p2 = (char*)calloc(0, 1);
-     printf ("p2 is %p\n", p2);
-     printf ("Content of p2 is: %d\n", *p2);
-     // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
-     // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
-     free(p2);
+    char *p2 = (char *)calloc(0, 1);
+    printf("p2 is %p\n", p2);
+    printf("Content of p2 is: %d\n", *p2);
+    // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+    // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
+    free(p2);
   }
 
   {
-     char* p3 = (char*)malloc(0);
-     printf ("p3 is %p\n", p3);
-     printf ("Content of p2 is: %d\n", *p3);
-     // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
-     // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
-     free(p3);
+    char *p3 = (char *)malloc(0);
+    printf("p3 is %p\n", p3);
+    printf("Content of p2 is: %d\n", *p3);
+    // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+    // CHECK: {{#0 0x.* in main .*zero_alloc.cpp:}}[[@LINE-2]]
+    free(p3);
   }
 
   return 0;

From 89e196e1c57d94fb9143db3dc7840e9b0ba211db Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston@google.com>
Date: Thu, 28 Aug 2025 22:24:15 +0000
Subject: [PATCH 3/3] Add note on bad compilers

---
 compiler-rt/test/msan/zero_alloc.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler-rt/test/msan/zero_alloc.cpp b/compiler-rt/test/msan/zero_alloc.cpp
index 6a3ce26e256b7..e60051872eba2 100644
--- a/compiler-rt/test/msan/zero_alloc.cpp
+++ b/compiler-rt/test/msan/zero_alloc.cpp
@@ -1,5 +1,7 @@
 // RUN: %clang_msan -Wno-alloc-size -fsanitize-recover=memory %s -o %t && not %run %t 2>&1 | FileCheck %s
 
+// MSan doesn't catch this because internally it translates 0-byte allocations
+// into 1-byte
 // XFAIL: *
 
 #include <malloc.h>