[LLVMbugs] [Bug 10427] New: clang should warn if a macro argument expansion is "obviously" missing parentheses

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=10427

           Summary: clang should warn if a macro argument expansion is
                    "obviously" missing parentheses
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: nicolasweber at gmx.de
                CC: llvmbugs at cs.uiuc.edu


Consider this bug from the valgrind sources:

hummer:src thakis$ cat test.c
#include <stdio.h>

struct vki_timeval {
  int a, b, c, d, e;
};

#define PRE_timeval_READ(zzname, zzarg)                        \
   do {                                                        \
      struct vki_timeval *zztv = (struct vki_timeval *)zzarg;  \
      printf("Note: %s %d\n", zzname, zztv->c);                \
   } while (0)

int main() {
  struct vki_timeval vals[3] = {
    { 1, 1, 1, 1, 1 },
    { 2, 2, 2, 2, 2 },
    { 3, 3, 3, 3, 3 }
  };

  void* tvp = &vals[0];

  PRE_timeval_READ( "futimes(tvp[1])", tvp+sizeof(struct vki_timeval) );
}
hummer:src thakis$ gcc  test.c -o foo
hummer:src thakis$ ./foo
Note: futimes(tvp[1]) 1836213620



The fix for the bug is (note the added parens):

      struct vki_timeval *zztv = (struct vki_timeval *)(zzarg);  \


Clang could maybe warn if something in a macro (here: the cast) binds with a
high precendence to only parts of a macro argument (here
"tvp+sizeof(vki_timeval)") or some such.

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