[LLVMbugs] [Bug 9426] New: change __builtin_object_size prototype

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Mar 8 07:12:03 PST 2011


           Summary: change __builtin_object_size prototype
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: pageexec at freemail.hu
                CC: llvmbugs at cs.uiuc.edu, pageexec at freemail.hu
            Blocks: 4068

while gcc declares __builtin_object_size as

  size_t __builtin_object_size (void * PTR, int TYPE)

it generates a warning in clang for 'const void *' PTR parameters (and
presumably for volatile ones too, although it's probably rare in practice, i
certainly didn't see it trigger in linux) when compiling linux:

arch/x86/include/asm/uaccess_32.h:241:11: warning: passing 'const void *' to
parameter of type 'void *' discards qualifiers
        int sz = __compiletime_object_size(from);

include/linux/compiler-gcc4.h:64:62: note: instantiated from:
#define __compiletime_object_size(obj) __builtin_object_size((obj), 0)

now one can fix this macro by adding an explicit (void *) cast for 'obj' but
i'd suggest to change the builtin's prototype in clang itself since this
builtin function really doesn't need a non-const pointer for its job:

--- llvm/tools/clang/include/clang/Basic/Builtins.def        (revision 127235)
+++ llvm/tools/clang/include/clang/Basic/Builtins.def        (working copy)
@@ -443,7 +443,7 @@
 BUILTIN(__builtin_extend_pointer, "ULLiv*", "n") // _Unwind_Word == uint64_t

 // GCC Object size checking builtins
-BUILTIN(__builtin_object_size, "zv*i", "n")
+BUILTIN(__builtin_object_size, "zvC*i", "n")
 BUILTIN(__builtin___memcpy_chk, "v*v*vC*zz", "nF")
 BUILTIN(__builtin___memmove_chk, "v*v*vC*zz", "nF")
 BUILTIN(__builtin___mempcpy_chk, "v*v*vC*zz", "nF")

and perhaps add 'D' too for handling volatile pointers as well.

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