[PATCH] D135989: [clang][Sema] Use size of char for void types

[Bill Wendling via Phabricator via cfe-commits]

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The extension that allows for pointer arithmetic on 'void' types treats
the 'void' as a 'char'. We should use the 'char' size instead of one in
this case to allow warning when pointer arithmetic would go out of
bounds.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135989

Files:
  clang/lib/Sema/SemaChecking.cpp
  clang/test/Sema/array-bounds-ptr-arith.c


Index: clang/test/Sema/array-bounds-ptr-arith.c
===================================================================
--- clang/test/Sema/array-bounds-ptr-arith.c
+++ clang/test/Sema/array-bounds-ptr-arith.c
@@ -6,13 +6,12 @@
 struct ext2_super_block{
   unsigned char s_uuid[8]; // expected-note {{declared here}}
 };
-void* ext2_statfs (struct ext2_super_block *es,int a)
-{
-	 return (void *)es->s_uuid + sizeof(int); // no-warning
+
+void* ext2_statfs (struct ext2_super_block *es,int a) {
+  return (void *)es->s_uuid + sizeof(int); // no-warning
 }
-void* broken (struct ext2_super_block *es,int a)
-{
-	 return (void *)es->s_uuid + 80; // expected-warning {{refers past the end of the array (that contains 8 elements)}}
+void* broken (struct ext2_super_block *es,int a) {
+  return (void *)es->s_uuid + 9; // expected-warning {{the pointer incremented by 9 refers past the end of the array (that contains 8 elements)}}
 }
 
 // Test case reduced from PR11594
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -16020,16 +16020,21 @@
     llvm::APInt size = ArrayTy->getSize();
 
     if (BaseType != EffectiveType) {
-      // Make sure we're comparing apples to apples when comparing index to size
+      // Make sure we're comparing apples to apples when comparing index to
+      // size.
       uint64_t ptrarith_typesize = Context.getTypeSize(EffectiveType);
       uint64_t array_typesize = Context.getTypeSize(BaseType);
-      // Handle ptrarith_typesize being zero, such as when casting to void*
-      if (!ptrarith_typesize) ptrarith_typesize = 1;
+
+      // Handle ptrarith_typesize being zero, such as when casting to void*.
+      if (!ptrarith_typesize)
+        ptrarith_typesize = Context.getCharWidth();
+
       if (ptrarith_typesize != array_typesize) {
-        // There's a cast to a different size type involved
+        // There's a cast to a different size type involved.
         uint64_t ratio = array_typesize / ptrarith_typesize;
+
         // TODO: Be smarter about handling cases where array_typesize is not a
-        // multiple of ptrarith_typesize
+        // multiple of ptrarith_typesize.
         if (ptrarith_typesize * ratio == array_typesize)
           size *= llvm::APInt(size.getBitWidth(), ratio);
       }


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