[clang] 91b3823 - [clang][Sema] Use size of char in bits for void types

[Bill Wendling via cfe-commits]

Author: Bill Wendling
Date: 2022-10-14T14:46:19-07:00
New Revision: 91b3823bd000b1a6ffde96a6363098f59307317a

URL: https://github.com/llvm/llvm-project/commit/91b3823bd000b1a6ffde96a6363098f59307317a
DIFF: https://github.com/llvm/llvm-project/commit/91b3823bd000b1a6ffde96a6363098f59307317a.diff

LOG: [clang][Sema] Use size of char in bits for void types

The extension that allows for pointer arithmetic on 'void' types treats
the 'void' as a 'char'. We should use the 'char' size in bits instead of
1 (the number of bytes) to allow warning when pointer arithmetic would
go out of bounds.

Differential Revision: https://reviews.llvm.org/D135989

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index a1e3db1b57af2..c0ecd7b091000 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -16020,16 +16020,22 @@ void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
     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*.
+      // Use the size in bits (what "getTypeSize()" returns) rather than bytes.
+      if (!ptrarith_typesize)
+        ptrarith_typesize = Context.getCharWidth();
+
       if (ptrarith_typesize != array_typesize) {
-        // There's a cast to a 
diff erent size type involved
+        // There's a cast to a 
diff erent 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);
       }

diff  --git a/clang/test/Sema/array-bounds-ptr-arith.c b/clang/test/Sema/array-bounds-ptr-arith.c
index a447f19dfe830..57baf9241cf0e 100644
--- a/clang/test/Sema/array-bounds-ptr-arith.c
+++ b/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}}
+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}}
 }
 
 // Test case reduced from PR11594